oracular (2) prctl.2.gz

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NAME

       prctl - operations on a process or thread

LIBRARY

       Standard C library (libc, -lc)

SYNOPSIS

       #include <sys/prctl.h>

       int prctl(int op, ...
                 /* unsigned long arg2, unsigned long arg3,
                 unsigned long arg4, unsigned long arg5 */ );

DESCRIPTION

       prctl() manipulates various aspects of the behavior of the calling thread or process.

       Note  that  careless  use  of some prctl() operations can confuse the user-space run-time environment, so
       these operations should be used with care.

       prctl() is called with a first argument describing what to do (with values defined  in  <linux/prctl.h>),
       and further arguments with a significance depending on the first one.  The first argument can be:

       PR_CAP_AMBIENT (since Linux 4.3)
              Reads or changes the ambient capability set of the calling thread, according to the value of arg2,
              which must be one of the following:

              PR_CAP_AMBIENT_RAISE
                     The capability specified in arg3 is added to the ambient  set.   The  specified  capability
                     must  already  be  present  in  both the permitted and the inheritable sets of the process.
                     This operation is not permitted if the SECBIT_NO_CAP_AMBIENT_RAISE securebit is set.

              PR_CAP_AMBIENT_LOWER
                     The capability specified in arg3 is removed from the ambient set.

              PR_CAP_AMBIENT_IS_SET
                     The prctl() call returns 1 if the capability in arg3 is in the ambient set and 0 if  it  is
                     not.

              PR_CAP_AMBIENT_CLEAR_ALL
                     All  capabilities  will  be  removed from the ambient set.  This operation requires setting
                     arg3 to zero.

              In all of the above operations, arg4 and arg5 must be specified as 0.

              Higher-level interfaces layered on top of the above  operations  are  provided  in  the  libcap(3)
              library in the form of cap_get_ambient(3), cap_set_ambient(3), and cap_reset_ambient(3).

       PR_CAPBSET_READ (since Linux 2.6.25)
              Return  (as  the function result) 1 if the capability specified in arg2 is in the calling thread's
              capability bounding  set,  or  0  if  it  is  not.   (The  capability  constants  are  defined  in
              <linux/capability.h>.)   The  capability bounding set dictates whether the process can receive the
              capability through a file's permitted capability set on a subsequent call to execve(2).

              If the capability specified in arg2 is not valid, then the call fails with the error EINVAL.

              A higher-level interface layered on top of this operation is provided in the libcap(3) library  in
              the form of cap_get_bound(3).

       PR_CAPBSET_DROP (since Linux 2.6.25)
              If  the  calling  thread  has  the CAP_SETPCAP capability within its user namespace, then drop the
              capability specified by arg2 from the calling thread's capability bounding set.  Any  children  of
              the calling thread will inherit the newly reduced bounding set.

              The  call  fails with the error: EPERM if the calling thread does not have the CAP_SETPCAP; EINVAL
              if arg2 does not represent a valid capability; or EINVAL if file capabilities are not  enabled  in
              the kernel, in which case bounding sets are not supported.

              A  higher-level interface layered on top of this operation is provided in the libcap(3) library in
              the form of cap_drop_bound(3).

       PR_SET_CHILD_SUBREAPER (since Linux 3.4)
              If arg2 is nonzero, set the "child subreaper" attribute of the calling process; if arg2  is  zero,
              unset the attribute.

              A  subreaper  fulfills  the  role of init(1) for its descendant processes.  When a process becomes
              orphaned (i.e., its immediate parent terminates), then that process  will  be  reparented  to  the
              nearest  still  living  ancestor  subreaper.   Subsequently,  calls  to getppid(2) in the orphaned
              process will now return the PID of the subreaper process, and when the orphan  terminates,  it  is
              the  subreaper  process  that  will  receive  a  SIGCHLD signal and will be able to wait(2) on the
              process to discover its termination status.

              The setting of the "child subreaper" attribute is not inherited by children created by fork(2) and
              clone(2).  The setting is preserved across execve(2).

              Establishing  a  subreaper process is useful in session management frameworks where a hierarchical
              group of processes is managed by a subreaper process that needs to be informed  when  one  of  the
              processes—for  example,  a  double-forked  daemon—terminates  (perhaps so that it can restart that
              process).  Some init(1) frameworks (e.g., systemd(1))  employ  a  subreaper  process  for  similar
              reasons.

       PR_GET_CHILD_SUBREAPER (since Linux 3.4)
              Return the "child subreaper" setting of the caller, in the location pointed to by (int *) arg2.

       PR_SET_DUMPABLE (since Linux 2.3.20)
              Set  the  state  of the "dumpable" attribute, which determines whether core dumps are produced for
              the calling process upon delivery of a signal whose default behavior is to produce a core dump.

              Up to and including Linux 2.6.12, arg2  must  be  either  0  (SUID_DUMP_DISABLE,  process  is  not
              dumpable)  or 1 (SUID_DUMP_USER, process is dumpable).  Between Linux 2.6.13 and Linux 2.6.17, the
              value 2 was also permitted, which caused any binary which normally  would  not  be  dumped  to  be
              dumped  readable by root only; for security reasons, this feature has been removed.  (See also the
              description of /proc/sys/fs/suid_dumpable in proc(5).)

              Normally, the "dumpable" attribute is set to 1.   However,  it  is  reset  to  the  current  value
              contained  in  the  file  /proc/sys/fs/suid_dumpable  (which  by  default has the value 0), in the
              following circumstances:

              •  The process's effective user or group ID is changed.

              •  The process's filesystem user or group ID is changed (see credentials(7)).

              •  The process executes (execve(2)) a set-user-ID or set-group-ID program, resulting in  a  change
                 of either the effective user ID or the effective group ID.

              •  The  process  executes  (execve(2)) a program that has file capabilities (see capabilities(7)),
                 but only if the permitted capabilities gained exceed those already permitted for the process.

              Processes that are not dumpable can not be attached via ptrace(2) PTRACE_ATTACH; see ptrace(2) for
              further details.

              If  a  process  is  not  dumpable,  the ownership of files in the process's /proc/pid directory is
              affected as described in proc(5).

       PR_GET_DUMPABLE (since Linux 2.3.20)
              Return (as the function result) the current state of the calling process's dumpable attribute.

       PR_SET_ENDIAN (since Linux 2.6.18, PowerPC only)
              Set the endian-ness of the calling process to the value given in arg2, which should be one of  the
              following:   PR_ENDIAN_BIG,  PR_ENDIAN_LITTLE,  or  PR_ENDIAN_PPC_LITTLE  (PowerPC  pseudo  little
              endian).

       PR_GET_ENDIAN (since Linux 2.6.18, PowerPC only)
              Return the endian-ness of the calling process, in the location pointed to by (int *) arg2.

       PR_SET_FP_MODE (since Linux 4.0, only on MIPS)
              On the MIPS architecture, user-space code can be built using an ABI  which  permits  linking  with
              code that has more restrictive floating-point (FP) requirements.  For example, user-space code may
              be built to target the O32 FPXX ABI and linked  with  code  built  for  either  one  of  the  more
              restrictive  FP32  or FP64 ABIs.  When more restrictive code is linked in, the overall requirement
              for the process is to use the more restrictive floating-point mode.

              Because the kernel has no means of knowing in advance which mode the process  should  be  executed
              in, and because these restrictions can change over the lifetime of the process, the PR_SET_FP_MODE
              operation is provided to allow control of the floating-point mode from user space.

              The (unsigned int) arg2 argument is a bit mask describing the floating-point mode used:

              PR_FP_MODE_FR
                     When this bit is unset (so called FR=0 or FR0 mode), the 32 floating-point registers are 32
                     bits  wide,  and  64-bit  registers  are represented as a pair of registers (even- and odd-
                     numbered, with the even-numbered register containing  the  lower  32  bits,  and  the  odd-
                     numbered register containing the higher 32 bits).

                     When  this  bit is set (on supported hardware), the 32 floating-point registers are 64 bits
                     wide (so called FR=1 or FR1 mode).  Note that modern  MIPS  implementations  (MIPS  R6  and
                     newer) support FR=1 mode only.

                     Applications  that  use  the O32 FP32 ABI can operate only when this bit is unset (FR=0; or
                     they can be used with FRE enabled, see below).  Applications that use the O32 FP64 ABI (and
                     the  O32 FP64A ABI, which exists to provide the ability to operate with existing FP32 code;
                     see below) can operate only when this bit is set (FR=1).  Applications  that  use  the  O32
                     FPXX ABI can operate with either FR=0 or FR=1.

              PR_FP_MODE_FRE
                     Enable  emulation  of  32-bit  floating-point mode.  When this mode is enabled, it emulates
                     32-bit floating-point operations by  raising  a  reserved-instruction  exception  on  every
                     instruction  that  uses  32-bit  formats  and  the  kernel  then handles the instruction in
                     software.  (The problem lies in the discrepancy of handling  odd-numbered  registers  which
                     are  the  high  32  bits  of  64-bit registers with even numbers in FR=0 mode and the lower
                     32-bit parts of odd-numbered  64-bit  registers  in  FR=1  mode.)   Enabling  this  bit  is
                     necessary  when code with the O32 FP32 ABI should operate with code with compatible the O32
                     FPXX or O32 FP64A ABIs (which require FR=1 FPU mode)  or  when  it  is  executed  on  newer
                     hardware (MIPS R6 onwards) which lacks FR=0 mode support when a binary with the FP32 ABI is
                     used.

                     Note that this mode makes sense only when the FPU is in 64-bit mode (FR=1).

                     Note that the use of emulation inherently has a significant performance hit and  should  be
                     avoided if possible.

              In  the  N32/N64  ABI, 64-bit floating-point mode is always used, so FPU emulation is not required
              and the FPU always operates in FR=1 mode.

              This operation is mainly intended for use by the dynamic linker (ld.so(8)).

              The arguments arg3, arg4, and arg5 are ignored.

       PR_GET_FP_MODE (since Linux 4.0, only on MIPS)
              Return (as  the  function  result)  the  current  floating-point  mode  (see  the  description  of
              PR_SET_FP_MODE for details).

              On success, the call returns a bit mask which represents the current floating-point mode.

              The arguments arg2, arg3, arg4, and arg5 are ignored.

       PR_SET_FPEMU (since Linux 2.4.18, 2.5.9, only on ia64)
              Set  floating-point  emulation  control  bits  to arg2.  Pass PR_FPEMU_NOPRINT to silently emulate
              floating-point operation accesses, or PR_FPEMU_SIGFPE to not emulate floating-point operations and
              send SIGFPE instead.

       PR_GET_FPEMU (since Linux 2.4.18, 2.5.9, only on ia64)
              Return floating-point emulation control bits, in the location pointed to by (int *) arg2.

       PR_SET_FPEXC (since Linux 2.4.21, 2.5.32, only on PowerPC)
              Set floating-point exception mode to arg2.  Pass PR_FP_EXC_SW_ENABLE to use FPEXC for FP exception
              enables, PR_FP_EXC_DIV  for  floating-point  divide  by  zero,  PR_FP_EXC_OVF  for  floating-point
              overflow,  PR_FP_EXC_UND  for  floating-point  underflow, PR_FP_EXC_RES for floating-point inexact
              result, PR_FP_EXC_INV for floating-point invalid operation, PR_FP_EXC_DISABLED for  FP  exceptions
              disabled,  PR_FP_EXC_NONRECOV  for  async nonrecoverable exception mode, PR_FP_EXC_ASYNC for async
              recoverable exception mode, PR_FP_EXC_PRECISE for precise exception mode.

       PR_GET_FPEXC (since Linux 2.4.21, 2.5.32, only on PowerPC)
              Return floating-point exception mode, in the location pointed to by (int *) arg2.

       PR_SET_IO_FLUSHER (since Linux 5.6)
              If a user process is involved in the block layer or filesystem I/O path, and can  allocate  memory
              while  processing I/O requests it must set arg2 to 1.  This will put the process in the IO_FLUSHER
              state, which allows it special treatment to make progress when allocating memory.  If arg2  is  0,
              the process will clear the IO_FLUSHER state, and the default behavior will be used.

              The calling process must have the CAP_SYS_RESOURCE capability.

              arg3, arg4, and arg5 must be zero.

              The  IO_FLUSHER  state is inherited by a child process created via fork(2) and is preserved across
              execve(2).

              Examples of IO_FLUSHER applications are FUSE daemons, SCSI device emulation daemons,  and  daemons
              that perform error handling like multipath path recovery applications.

       PR_GET_IO_FLUSHER (Since Linux 5.6)
              Return  (as  the function result) the IO_FLUSHER state of the caller.  A value of 1 indicates that
              the caller is in the IO_FLUSHER state; 0 indicates that the caller is not in the IO_FLUSHER state.

              The calling process must have the CAP_SYS_RESOURCE capability.

              arg2, arg3, arg4, and arg5 must be zero.

       PR_SET_KEEPCAPS (since Linux 2.2.18)
              Set the state of the calling thread's "keep capabilities"  flag.   The  effect  of  this  flag  is
              described  in  capabilities(7).   arg2 must be either 0 (clear the flag) or 1 (set the flag).  The
              "keep capabilities" value will be reset to 0 on subsequent calls to execve(2).

       PR_GET_KEEPCAPS (since Linux 2.2.18)
              Return (as the function result) the current state of  the  calling  thread's  "keep  capabilities"
              flag.  See capabilities(7) for a description of this flag.

       PR_MCE_KILL (since Linux 2.6.32)
              Set  the  machine  check  memory  corruption  kill  policy  for  the  calling  thread.  If arg2 is
              PR_MCE_KILL_CLEAR, clear the thread memory corruption kill policy and use the system-wide default.
              (The  system-wide  default is defined by /proc/sys/vm/memory_failure_early_kill; see proc(5).)  If
              arg2 is PR_MCE_KILL_SET, use a thread-specific memory corruption kill policy.  In this case,  arg3
              defines whether the policy is early kill (PR_MCE_KILL_EARLY), late kill (PR_MCE_KILL_LATE), or the
              system-wide default (PR_MCE_KILL_DEFAULT).  Early kill means that the  thread  receives  a  SIGBUS
              signal  as  soon as hardware memory corruption is detected inside its address space.  In late kill
              mode, the process is killed only when it accesses a corrupted page.   See  sigaction(2)  for  more
              information  on  the  SIGBUS  signal.   The policy is inherited by children.  The remaining unused
              prctl() arguments must be zero for future compatibility.

       PR_MCE_KILL_GET (since Linux 2.6.32)
              Return (as the function result) the current per-process machine check  kill  policy.   All  unused
              prctl() arguments must be zero.

       PR_SET_MM (since Linux 3.3)
              Modify  certain  kernel memory map descriptor fields of the calling process.  Usually these fields
              are set by the kernel and dynamic loader  (see  ld.so(8)  for  more  information)  and  a  regular
              application  should  not  use  this  feature.   However,  there  are cases, such as self-modifying
              programs, where a program might find it useful to change its own memory map.

              The calling process must have the CAP_SYS_RESOURCE capability.  The value in arg2 is  one  of  the
              options  below,  while arg3 provides a new value for the option.  The arg4 and arg5 arguments must
              be zero if unused.

              Before  Linux  3.10,  this  feature  is  available  only  if  the  kernel  is   built   with   the
              CONFIG_CHECKPOINT_RESTORE option enabled.

              PR_SET_MM_START_CODE
                     Set  the  address above which the program text can run.  The corresponding memory area must
                     be readable and executable, but not writable or shareable (see mprotect(2) and mmap(2)  for
                     more information).

              PR_SET_MM_END_CODE
                     Set  the  address below which the program text can run.  The corresponding memory area must
                     be readable and executable, but not writable or shareable.

              PR_SET_MM_START_DATA
                     Set the address above which initialized and  uninitialized  (bss)  data  are  placed.   The
                     corresponding memory area must be readable and writable, but not executable or shareable.

              PR_SET_MM_END_DATA
                     Set  the  address  below  which  initialized  and uninitialized (bss) data are placed.  The
                     corresponding memory area must be readable and writable, but not executable or shareable.

              PR_SET_MM_START_STACK
                     Set the start address of the stack.  The corresponding memory area  must  be  readable  and
                     writable.

              PR_SET_MM_START_BRK
                     Set the address above which the program heap can be expanded with brk(2) call.  The address
                     must be greater than the ending address of the current program data segment.  In  addition,
                     the  combined  size of the resulting heap and the size of the data segment can't exceed the
                     RLIMIT_DATA resource limit (see setrlimit(2)).

              PR_SET_MM_BRK
                     Set the current brk(2) value.  The requirements for the address are the  same  as  for  the
                     PR_SET_MM_START_BRK option.

              The following options are available since Linux 3.5.

              PR_SET_MM_ARG_START
                     Set the address above which the program command line is placed.

              PR_SET_MM_ARG_END
                     Set the address below which the program command line is placed.

              PR_SET_MM_ENV_START
                     Set the address above which the program environment is placed.

              PR_SET_MM_ENV_END
                     Set the address below which the program environment is placed.

                     The  address  passed  with PR_SET_MM_ARG_START, PR_SET_MM_ARG_END, PR_SET_MM_ENV_START, and
                     PR_SET_MM_ENV_END should belong to a process stack area.  Thus,  the  corresponding  memory
                     area  must  be  readable,  writable,  and  (depending on the kernel configuration) have the
                     MAP_GROWSDOWN attribute set (see mmap(2)).

              PR_SET_MM_AUXV
                     Set a new auxiliary vector.  The arg3 argument should provide the address  of  the  vector.
                     The arg4 is the size of the vector.

              PR_SET_MM_EXE_FILE
                     Supersede  the /proc/pid/exe symbolic link with a new one pointing to a new executable file
                     identified by the file descriptor provided in arg3 argument.  The file descriptor should be
                     obtained with a regular open(2) call.

                     To  change  the  symbolic  link,  one  needs to unmap all existing executable memory areas,
                     including those created by the kernel itself (for example the  kernel  usually  creates  at
                     least one executable memory area for the ELF .text section).

                     In  Linux 4.9 and earlier, the PR_SET_MM_EXE_FILE operation can be performed only once in a
                     process's lifetime; attempting to perform the operation a second time results in the  error
                     EPERM.   This  restriction  was enforced for security reasons that were subsequently deemed
                     specious,  and  the  restriction  was  removed  in  Linux  4.10  because  some   user-space
                     applications needed to perform this operation more than once.

              The following options are available since Linux 3.18.

              PR_SET_MM_MAP
                     Provides  one-shot  access  to  all  the  addresses by passing in a struct prctl_mm_map (as
                     defined in <linux/prctl.h>).  The arg4 argument should provide the size of the struct.

                     This feature is available only if the kernel is built  with  the  CONFIG_CHECKPOINT_RESTORE
                     option enabled.

              PR_SET_MM_MAP_SIZE
                     Returns  the size of the struct prctl_mm_map the kernel expects.  This allows user space to
                     find a compatible struct.  The arg4 argument should be a pointer to an unsigned int.

                     This feature is available only if the kernel is built  with  the  CONFIG_CHECKPOINT_RESTORE
                     option enabled.

       PR_SET_VMA (since Linux 5.17)
              Sets  an  attribute specified in arg2 for virtual memory areas starting from the address specified
              in arg3 and spanning the size specified in arg4.  arg5 specifies the value of the attribute to  be
              set.

              Note  that assigning an attribute to a virtual memory area might prevent it from being merged with
              adjacent virtual memory areas due to the difference in that attribute's value.

              Currently, arg2 must be one of:

              PR_SET_VMA_ANON_NAME
                     Set a name for anonymous virtual memory areas.   arg5  should  be  a  pointer  to  a  null-
                     terminated  string  containing the name.  The name length including null byte cannot exceed
                     80 bytes.  If arg5 is NULL, the name of the appropriate anonymous virtual memory areas will
                     be  reset.   The name can contain only printable ascii characters (including space), except
                     '[', ']', '\', '$', and '`'.

       PR_MPX_ENABLE_MANAGEMENT
       PR_MPX_DISABLE_MANAGEMENT (since Linux 3.19, removed in Linux 5.4; only on x86)
              Enable or disable kernel management of Memory Protection  eXtensions  (MPX)  bounds  tables.   The
              arg2, arg3, arg4, and arg5 arguments must be zero.

              MPX is a hardware-assisted mechanism for performing bounds checking on pointers.  It consists of a
              set of registers storing bounds information and a set of special instruction  prefixes  that  tell
              the CPU on which instructions it should do bounds enforcement.  There is a limited number of these
              registers and when there are more pointers than registers, their contents must be "spilled" into a
              set  of  tables.   These  tables are called "bounds tables" and the MPX prctl() operations control
              whether the kernel manages their allocation and freeing.

              When management is enabled, the kernel will take over allocation and freeing of the bounds tables.
              It  does this by trapping the #BR exceptions that result at first use of missing bounds tables and
              instead of delivering the exception to user space, it allocates the table and populates the bounds
              directory  with  the  location  of the new table.  For freeing, the kernel checks to see if bounds
              tables are present for memory which is not allocated, and frees them if so.

              Before enabling MPX management using PR_MPX_ENABLE_MANAGEMENT, the  application  must  first  have
              allocated  a  user-space buffer for the bounds directory and placed the location of that directory
              in the bndcfgu register.

              These calls fail if the CPU or kernel does not support MPX.  Kernel support for MPX is enabled via
              the  CONFIG_X86_INTEL_MPX  configuration  option.   You  can check whether the CPU supports MPX by
              looking for the mpx CPUID bit, like with the following command:

                  cat /proc/cpuinfo | grep ' mpx '

              A thread may not switch in or out of long (64-bit) mode while MPX is enabled.

              All threads in a process are affected by these calls.

              The child of a fork(2) inherits the state of MPX management.  During execve(2), MPX management  is
              reset to a state as if PR_MPX_DISABLE_MANAGEMENT had been called.

              For further information on Intel MPX, see the kernel source file Documentation/x86/intel_mpx.txt.

              Due to a lack of toolchain support, PR_MPX_ENABLE_MANAGEMENT and PR_MPX_DISABLE_MANAGEMENT are not
              supported in Linux 5.4 and later.

       PR_SET_NAME (since Linux 2.6.9)
              Set the name of the calling thread, using the value in the location pointed to by (char  *)  arg2.
              The  name  can be up to 16 bytes long, including the terminating null byte.  (If the length of the
              string, including the terminating null byte, exceeds 16 bytes, the string is silently  truncated.)
              This  is  the  same  attribute  that  can  be  set  via  pthread_setname_np(3) and retrieved using
              pthread_getname_np(3).  The attribute is likewise  accessible  via  /proc/self/task/tid/comm  (see
              proc(5)), where tid is the thread ID of the calling thread, as returned by gettid(2).

       PR_GET_NAME (since Linux 2.6.11)
              Return  the  name  of  the  calling thread, in the buffer pointed to by (char *) arg2.  The buffer
              should allow space for up to 16 bytes; the returned string will be null-terminated.

       PR_SET_NO_NEW_PRIVS (since Linux 3.5)
              Set the calling thread's no_new_privs attribute to the value in arg2.  With no_new_privs set to 1,
              execve(2)  promises  not  to grant privileges to do anything that could not have been done without
              the execve(2) call (for example, rendering the set-user-ID and set-group-ID mode  bits,  and  file
              capabilities  non-functional).  Once set, the no_new_privs attribute cannot be unset.  The setting
              of this attribute is inherited by children created by fork(2) and clone(2), and  preserved  across
              execve(2).

              Since  Linux 4.10, the value of a thread's no_new_privs attribute can be viewed via the NoNewPrivs
              field in the /proc/pid/status file.

              For more information, see the kernel source file Documentation/userspace-api/no_new_privs.rst  (or
              Documentation/prctl/no_new_privs.txt before Linux 4.13).  See also seccomp(2).

       PR_GET_NO_NEW_PRIVS (since Linux 3.5)
              Return (as the function result) the value of the no_new_privs attribute for the calling thread.  A
              value of 0 indicates the regular execve(2) behavior.   A  value  of  1  indicates  execve(2)  will
              operate in the privilege-restricting mode described above.

       PR_PAC_RESET_KEYS (since Linux 5.0, only on arm64)
              Securely  reset  the  thread's pointer authentication keys to fresh random values generated by the
              kernel.

              The set of keys to be reset is specified by arg2, which must be a logical OR of zero  or  more  of
              the following:

              PR_PAC_APIAKEY
                     instruction authentication key A

              PR_PAC_APIBKEY
                     instruction authentication key B

              PR_PAC_APDAKEY
                     data authentication key A

              PR_PAC_APDBKEY
                     data authentication key B

              PR_PAC_APGAKEY
                     generic authentication “A” key.

                     (Yes folks, there really is no generic B key.)

              As a special case, if arg2 is zero, then all the keys are reset.  Since new keys could be added in
              future, this is the recommended way to completely wipe the existing keys when establishing a clean
              execution context.  Note that there is no need to use PR_PAC_RESET_KEYS in preparation for calling
              execve(2), since execve(2) resets all the pointer authentication keys.

              The remaining arguments arg3, arg4, and arg5 must all be zero.

              If the arguments are invalid, and in particular if arg2 contains set bits that are unrecognized or
              that correspond to a key not available on this platform, then the call fails with error EINVAL.

              Warning:  Because  the  compiler  or  run-time environment may be using some or all of the keys, a
              successful PR_PAC_RESET_KEYS may crash the calling process.  The conditions for  using  it  safely
              are complex and system-dependent.  Don't use it unless you know what you are doing.

              For  more  information,  see the kernel source file Documentation/arm64/pointer-authentication.rst
              (or Documentation/arm64/pointer-authentication.txt before Linux 5.3).

       PR_SET_PDEATHSIG (since Linux 2.1.57)
              Set the parent-death signal of the calling process to arg2 (either a signal value in the range [1,
              NSIG  -  1], or 0 to clear).  This is the signal that the calling process will get when its parent
              dies.

              Warning: the "parent" in this case is considered to be the thread that created this  process.   In
              other   words,   the  signal  will  be  sent  when  that  thread  terminates  (via,  for  example,
              pthread_exit(3)), rather than after all of the threads in the parent process terminate.

              The parent-death signal is sent upon subsequent termination of the parent  thread  and  also  upon
              termination  of  each  subreaper  process (see the description of PR_SET_CHILD_SUBREAPER above) to
              which the caller is subsequently reparented.  If the parent thread  and  all  ancestor  subreapers
              have already terminated by the time of the PR_SET_PDEATHSIG operation, then no parent-death signal
              is sent to the caller.

              The parent-death signal is process-directed (see signal(7)) and, if the child installs  a  handler
              using  the sigaction(2) SA_SIGINFO flag, the si_pid field of the siginfo_t argument of the handler
              contains the PID of the terminating parent process.

              The parent-death signal setting is cleared for the child of a fork(2).  It is  also  (since  Linux
              2.4.36 / 2.6.23) cleared when executing a set-user-ID or set-group-ID binary, or a binary that has
              associated  capabilities  (see  capabilities(7));  otherwise,  this  value  is  preserved   across
              execve(2).   The  parent-death signal setting is also cleared upon changes to any of the following
              thread credentials: effective user ID, effective group ID, filesystem user ID, or filesystem group
              ID.

       PR_GET_PDEATHSIG (since Linux 2.3.15)
              Return the current value of the parent process death signal, in the location pointed to by (int *)
              arg2.

       PR_SET_PTRACER (since Linux 3.4)
              This is meaningful only when the Yama LSM is enabled and in mode 1 ("restricted  ptrace",  visible
              via  /proc/sys/kernel/yama/ptrace_scope).   When  a  "ptracer  process  ID" is passed in arg2, the
              caller is declaring that the ptracer process can ptrace(2) the calling process as  if  it  were  a
              direct  process  ancestor.   Each  PR_SET_PTRACER operation replaces the previous "ptracer process
              ID".  Employing PR_SET_PTRACER with arg2 set to 0 clears the caller's "ptracer  process  ID".   If
              arg2  is  PR_SET_PTRACER_ANY,  the ptrace restrictions introduced by Yama are effectively disabled
              for the calling process.

              For further information, see the kernel  source  file  Documentation/admin-guide/LSM/Yama.rst  (or
              Documentation/security/Yama.txt before Linux 4.13).

       PR_SET_SECCOMP (since Linux 2.6.23)
              Set  the  secure  computing  (seccomp)  mode for the calling thread, to limit the available system
              calls.  The more recent seccomp(2) system  call  provides  a  superset  of  the  functionality  of
              PR_SET_SECCOMP, and is the preferred interface for new applications.

              The  seccomp mode is selected via arg2.  (The seccomp constants are defined in <linux/seccomp.h>.)
              The following values can be specified:

              SECCOMP_MODE_STRICT (since Linux 2.6.23)
                     See the description of SECCOMP_SET_MODE_STRICT in seccomp(2).

                     This operation is available only if the kernel is configured with CONFIG_SECCOMP enabled.

              SECCOMP_MODE_FILTER (since Linux 3.5)
                     The allowed system calls are defined by a pointer to a Berkeley  Packet  Filter  passed  in
                     arg3.   This  argument  is  a  pointer  to  struct sock_fprog; it can be designed to filter
                     arbitrary  system  calls   and   system   call   arguments.    See   the   description   of
                     SECCOMP_SET_MODE_FILTER in seccomp(2).

                     This  operation  is  available  only if the kernel is configured with CONFIG_SECCOMP_FILTER
                     enabled.

              For further details on seccomp filtering, see seccomp(2).

       PR_GET_SECCOMP (since Linux 2.6.23)
              Return (as the function result) the secure computing mode of the calling thread.  If the caller is
              not  in  secure  computing  mode,  this  operation  returns  0;  if the caller is in strict secure
              computing mode, then the prctl() call will cause a SIGKILL signal to be sent to the  process.   If
              the  caller  is in filter mode, and this system call is allowed by the seccomp filters, it returns
              2; otherwise, the process is killed with a SIGKILL signal.

              This operation is available only if the kernel is configured with CONFIG_SECCOMP enabled.

              Since Linux 3.8, the Seccomp field of the /proc/pid/status file provides a method of obtaining the
              same information, without the risk that the process is killed; see proc(5).

       PR_SET_SECUREBITS (since Linux 2.6.26)
              Set  the  "securebits"  flags  of  the  calling  thread  to  the  value  supplied  in  arg2.   See
              capabilities(7).

       PR_GET_SECUREBITS (since Linux 2.6.26)
              Return  (as  the  function  result)  the  "securebits"  flags  of   the   calling   thread.    See
              capabilities(7).

       PR_GET_SPECULATION_CTRL (since Linux 4.17)
              Return  (as  the  function  result)  the  state  of  the speculation misfeature specified in arg2.
              Currently, the only permitted value for this argument is PR_SPEC_STORE_BYPASS (otherwise the  call
              fails with the error ENODEV).

              The return value uses bits 0-3 with the following meaning:

              PR_SPEC_PRCTL
                     Mitigation can be controlled per thread by PR_SET_SPECULATION_CTRL.

              PR_SPEC_ENABLE
                     The speculation feature is enabled, mitigation is disabled.

              PR_SPEC_DISABLE
                     The speculation feature is disabled, mitigation is enabled.

              PR_SPEC_FORCE_DISABLE
                     Same as PR_SPEC_DISABLE but cannot be undone.

              PR_SPEC_DISABLE_NOEXEC (since Linux 5.1)
                     Same as PR_SPEC_DISABLE, but the state will be cleared on execve(2).

              If all bits are 0, then the CPU is not affected by the speculation misfeature.

              If  PR_SPEC_PRCTL  is  set,  then  per-thread control of the mitigation is available.  If not set,
              prctl() for the speculation misfeature will fail.

              The arg3, arg4, and arg5 arguments must be specified as 0; otherwise the call fails with the error
              EINVAL.

       PR_SET_SPECULATION_CTRL (since Linux 4.17)
              Sets  the  state  of  the  speculation  misfeature  specified in arg2.  The speculation-misfeature
              settings are per-thread attributes.

              Currently, arg2 must be one of:

              PR_SPEC_STORE_BYPASS
                     Set the state of the speculative store bypass misfeature.

              PR_SPEC_INDIRECT_BRANCH (since Linux 4.20)
                     Set the state of the indirect branch speculation misfeature.

              If arg2 does not have one of the above values, then the call fails with the error ENODEV.

              The arg3 argument is used to hand in the control value, which is one of the following:

              PR_SPEC_ENABLE
                     The speculation feature is enabled, mitigation is disabled.

              PR_SPEC_DISABLE
                     The speculation feature is disabled, mitigation is enabled.

              PR_SPEC_FORCE_DISABLE
                     Same as PR_SPEC_DISABLE, but cannot be undone.  A  subsequent  prctl(arg2,  PR_SPEC_ENABLE)
                     with the same value for arg2 will fail with the error EPERM.

              PR_SPEC_DISABLE_NOEXEC (since Linux 5.1)
                     Same  as  PR_SPEC_DISABLE,  but  the  state  will  be cleared on execve(2).  Currently only
                     supported for arg2 equal to PR_SPEC_STORE_BYPASS.

              Any unsupported value in arg3 will result in the call failing with the error ERANGE.

              The arg4 and arg5 arguments must be specified as 0;  otherwise  the  call  fails  with  the  error
              EINVAL.

              The  speculation  feature  can also be controlled by the spec_store_bypass_disable boot parameter.
              This parameter may enforce a read-only policy which will result in the prctl() call  failing  with
              the     error     ENXIO.      For    further    details,    see    the    kernel    source    file
              Documentation/admin-guide/kernel-parameters.txt.

       PR_SVE_SET_VL (since Linux 4.15, only on arm64)
              Configure the thread's SVE vector length, as specified by (int) arg2.  Arguments arg3,  arg4,  and
              arg5 are ignored.

              The  bits  of arg2 corresponding to PR_SVE_VL_LEN_MASK must be set to the desired vector length in
              bytes.  This is interpreted as an upper bound: the  kernel  will  select  the  greatest  available
              vector  length  that  does  not  exceed the value specified.  In particular, specifying SVE_VL_MAX
              (defined in <asm/sigcontext.h>) for the PR_SVE_VL_LEN_MASK bits  requests  the  maximum  supported
              vector length.

              In addition, the other bits of arg2 must be set to one of the following combinations of flags:

              0      Perform  the  change  immediately.   At the next execve(2) in the thread, the vector length
                     will be reset to the value configured in /proc/sys/abi/sve_default_vector_length.

              PR_SVE_VL_INHERIT
                     Perform the change immediately.  Subsequent execve(2) calls will preserve  the  new  vector
                     length.

              PR_SVE_SET_VL_ONEXEC
                     Defer  the  change,  so  that it is performed at the next execve(2) in the thread.  Further
                     execve(2)  calls  will   reset   the   vector   length   to   the   value   configured   in
                     /proc/sys/abi/sve_default_vector_length.

              PR_SVE_SET_VL_ONEXEC | PR_SVE_VL_INHERIT
                     Defer  the  change,  so  that it is performed at the next execve(2) in the thread.  Further
                     execve(2) calls will preserve the new vector length.

              In all cases, any previously pending deferred change is canceled.

              The call fails with error EINVAL if SVE is not supported on the platform, if arg2 is  unrecognized
              or  invalid,  or  the value in the bits of arg2 corresponding to PR_SVE_VL_LEN_MASK is outside the
              range SVE_VL_MIN..SVE_VL_MAX or is not a multiple of 16.

              On success, a nonnegative value  is  returned  that  describes  the  selected  configuration.   If
              PR_SVE_SET_VL_ONEXEC  was  included  in arg2, then the configuration described by the return value
              will take effect at the next execve(2).  Otherwise, the configuration is already  in  effect  when
              the  PR_SVE_SET_VL  call  returns.   In  either  case, the value is encoded in the same way as the
              return value of PR_SVE_GET_VL.   Note  that  there  is  no  explicit  flag  in  the  return  value
              corresponding to PR_SVE_SET_VL_ONEXEC.

              The  configuration  (including  any  pending  deferred  change)  is  inherited  across fork(2) and
              clone(2).

              For   more   information,   see   the   kernel   source   file   Documentation/arm64/sve.rst   (or
              Documentation/arm64/sve.txt before Linux 5.3).

              Warning:  Because  the  compiler or run-time environment may be using SVE, using this call without
              the PR_SVE_SET_VL_ONEXEC flag may crash the calling process.  The conditions for using  it  safely
              are complex and system-dependent.  Don't use it unless you really know what you are doing.

       PR_SVE_GET_VL (since Linux 4.15, only on arm64)
              Get the thread's current SVE vector length configuration.

              Arguments arg2, arg3, arg4, and arg5 are ignored.

              Provided  that  the  kernel  and platform support SVE, this operation always succeeds, returning a
              nonnegative  value  that  describes  the  current  configuration.   The  bits   corresponding   to
              PR_SVE_VL_LEN_MASK contain the currently configured vector length in bytes.  The bit corresponding
              to PR_SVE_VL_INHERIT indicates whether the vector length will be inherited across execve(2).

              Note that there is no way to determine whether there is a pending vector length  change  that  has
              not yet taken effect.

              For   more   information,   see   the   kernel   source   file   Documentation/arm64/sve.rst   (or
              Documentation/arm64/sve.txt before Linux 5.3).

       PR_SET_SYSCALL_USER_DISPATCH (since Linux 5.11, x86 only)
              Configure the Syscall User Dispatch mechanism for the calling thread.  This  mechanism  allows  an
              application  to  selectively  intercept  system  calls  so  that  they  can  be handled within the
              application itself.  Interception takes the form  of  a  thread-directed  SIGSYS  signal  that  is
              delivered  to  the  thread  when  it  makes a system call.  If intercepted, the system call is not
              executed by the kernel.

              To enable this mechanism, arg2 should be set to PR_SYS_DISPATCH_ON.  Once enabled, further  system
              calls will be selectively intercepted, depending on a control variable provided by user space.  In
              this case, arg3 and arg4 respectively identify the offset and length of a single contiguous memory
              region  in  the  process  address space from where system calls are always allowed to be executed,
              regardless of the control variable.  (Typically, this  area  would  include  the  area  of  memory
              containing the C library.)

              arg5  points  to  a char-sized variable that is a fast switch to allow/block system call execution
              without the overhead of doing another system call to re-configure  Syscall  User  Dispatch.   This
              control  variable  can  either  be set to SYSCALL_DISPATCH_FILTER_BLOCK to block system calls from
              executing or to SYSCALL_DISPATCH_FILTER_ALLOW to temporarily allow  them  to  be  executed.   This
              value  is checked by the kernel on every system call entry, and any unexpected value will raise an
              uncatchable SIGSYS at that time, killing the application.

              When a system call is intercepted, the  kernel  sends  a  thread-directed  SIGSYS  signal  to  the
              triggering  thread.   Various  fields  will  be  set in the siginfo_t structure (see sigaction(2))
              associated with the signal:

              •  si_signo will contain SIGSYS.

              •  si_call_addr will show the address of the system call instruction.

              •  si_syscall and si_arch will indicate which system call was attempted.

              •  si_code will contain SYS_USER_DISPATCH.

              •  si_errno will be set to 0.

              The program counter will be as though the system call happened (i.e., the program counter will not
              point to the system call instruction).

              When  the  signal handler returns to the kernel, the system call completes immediately and returns
              to the calling thread, without actually being executed.  If necessary (i.e.,  when  emulating  the
              system  call on user space.), the signal handler should set the system call return value to a sane
              value, by modifying the register context stored in the ucontext argument of  the  signal  handler.
              See sigaction(2), sigreturn(2), and getcontext(3) for more information.

              If  arg2  is  set  to PR_SYS_DISPATCH_OFF, Syscall User Dispatch is disabled for that thread.  the
              remaining arguments must be set to 0.

              The setting is not preserved across fork(2), clone(2), or execve(2).

              For        more        information,        see        the        kernel        source         file
              Documentation/admin-guide/syscall-user-dispatch.rst

       PR_SET_TAGGED_ADDR_CTRL (since Linux 5.4, only on arm64)
              Controls support for passing tagged user-space addresses to the kernel (i.e., addresses where bits
              56—63 are not all zero).

              The level of support is selected by arg2, which can be one of the following:

              0      Addresses that are passed for the purpose of being  dereferenced  by  the  kernel  must  be
                     untagged.

              PR_TAGGED_ADDR_ENABLE
                     Addresses  that  are  passed  for  the  purpose  of being dereferenced by the kernel may be
                     tagged, with the exceptions summarized below.

              The remaining arguments arg3, arg4, and arg5 must all be zero.

              On success, the mode specified in arg2 is set for the calling thread and the return  value  is  0.
              If  the  arguments  are invalid, the mode specified in arg2 is unrecognized, or if this feature is
              unsupported by the kernel or disabled via /proc/sys/abi/tagged_addr_disabled, the call fails  with
              the error EINVAL.

              In particular, if prctl(PR_SET_TAGGED_ADDR_CTRL, 0, 0, 0, 0) fails with EINVAL, then all addresses
              passed to the kernel must be untagged.

              Irrespective of which mode is set, addresses passed to certain interfaces must always be untagged:

              •  brk(2), mmap(2), shmat(2), shmdt(2), and the new_address argument of mremap(2).

                 (Prior to Linux 5.6 these accepted tagged addresses, but the behaviour  may  not  be  what  you
                 expect.  Don't rely on it.)

              •  ‘polymorphic’  interfaces  that  accept  pointers  to arbitrary types cast to a void * or other
                 generic type, specifically prctl(),  ioctl(2),  and  in  general  setsockopt(2)  (only  certain
                 specific setsockopt(2) options allow tagged addresses).

              This  list of exclusions may shrink when moving from one kernel version to a later kernel version.
              While the kernel may make some guarantees for backwards compatibility reasons, for the purposes of
              new software the effect of passing tagged addresses to these interfaces is unspecified.

              The  mode  set  by  this  call  is  inherited  across  fork(2) and clone(2).  The mode is reset by
              execve(2) to 0 (i.e., tagged addresses not permitted in the user/kernel ABI).

              For more information, see the kernel source file Documentation/arm64/tagged-address-abi.rst.

              Warning: This call is primarily intended for  use  by  the  run-time  environment.   A  successful
              PR_SET_TAGGED_ADDR_CTRL call elsewhere may crash the calling process.  The conditions for using it
              safely are complex and system-dependent.  Don't use it unless you know what you are doing.

       PR_GET_TAGGED_ADDR_CTRL (since Linux 5.4, only on arm64)
              Returns the current tagged address mode for the calling thread.

              Arguments arg2, arg3, arg4, and arg5 must all be zero.

              If the arguments are invalid or this feature is disabled or unsupported by the  kernel,  the  call
              fails  with  EINVAL.   In  particular,  if  prctl(PR_GET_TAGGED_ADDR_CTRL,  0, 0, 0, 0) fails with
              EINVAL,   then   this   feature   is   definitely   either   unsupported,    or    disabled    via
              /proc/sys/abi/tagged_addr_disabled.   In  this  case,  all  addresses passed to the kernel must be
              untagged.

              Otherwise, the call returns a nonnegative  value  describing  the  current  tagged  address  mode,
              encoded in the same way as the arg2 argument of PR_SET_TAGGED_ADDR_CTRL.

              For more information, see the kernel source file Documentation/arm64/tagged-address-abi.rst.

       PR_TASK_PERF_EVENTS_DISABLE (since Linux 2.6.31)
              Disable  all  performance  counters  attached  to  the  calling process, regardless of whether the
              counters were created by this process or another process.  Performance  counters  created  by  the
              calling process for other processes are unaffected.  For more information on performance counters,
              see the Linux kernel source file tools/perf/design.txt.

              Originally called PR_TASK_PERF_COUNTERS_DISABLE; renamed (retaining the same numerical  value)  in
              Linux 2.6.32.

       PR_TASK_PERF_EVENTS_ENABLE (since Linux 2.6.31)
              The  converse  of PR_TASK_PERF_EVENTS_DISABLE; enable performance counters attached to the calling
              process.

              Originally called PR_TASK_PERF_COUNTERS_ENABLE; renamed in Linux 2.6.32.

       PR_SET_THP_DISABLE (since Linux 3.15)
              Set the state of the "THP disable" flag for the calling thread.  If arg2 has a nonzero value,  the
              flag  is  set,  otherwise  it  is  cleared.   Setting  this  flag  provides a method for disabling
              transparent huge pages for jobs where the code cannot be modified, and using a  malloc  hook  with
              madvise(2)  is  not an option (i.e., statically allocated data).  The setting of the "THP disable"
              flag is inherited by a child created via fork(2) and is preserved across execve(2).

       PR_GET_THP_DISABLE (since Linux 3.15)
              Return (as the function result) the current setting of the "THP  disable"  flag  for  the  calling
              thread: either 1, if the flag is set, or 0, if it is not.

       PR_GET_TID_ADDRESS (since Linux 3.5)
              Return the clear_child_tid address set by set_tid_address(2) and the clone(2) CLONE_CHILD_CLEARTID
              flag, in the location pointed to by (int **) arg2.  This feature is available only if  the  kernel
              is  built  with  the CONFIG_CHECKPOINT_RESTORE option enabled.  Note that since the prctl() system
              call does not have a compat implementation for the AMD64 x32 and MIPS n32  ABIs,  and  the  kernel
              writes  out  a pointer using the kernel's pointer size, this operation expects a user-space buffer
              of 8 (not 4) bytes on these ABIs.

       PR_SET_TIMERSLACK (since Linux 2.6.28)
              Each thread has two associated timer slack values: a "default" value, and a "current" value.  This
              operation  sets  the "current" timer slack value for the calling thread.  arg2 is an unsigned long
              value, then maximum "current" value is ULONG_MAX and the minimum "current" value  is  1.   If  the
              nanosecond  value  supplied  in arg2 is greater than zero, then the "current" value is set to this
              value.  If arg2 is equal to zero, the "current" timer slack is reset  to  the  thread's  "default"
              timer slack value.

              The  "current" timer slack is used by the kernel to group timer expirations for the calling thread
              that are close to one another; as a consequence, timer expirations for the thread may be up to the
              specified  number  of  nanoseconds late (but will never expire early).  Grouping timer expirations
              can help reduce system power consumption by minimizing CPU wake-ups.

              The timer expirations affected by timer slack are those set  by  select(2),  pselect(2),  poll(2),
              ppoll(2),  epoll_wait(2), epoll_pwait(2), clock_nanosleep(2), nanosleep(2), and futex(2) (and thus
              the   library   functions   implemented   via   futexes,   including    pthread_cond_timedwait(3),
              pthread_mutex_timedlock(3),   pthread_rwlock_timedrdlock(3),   pthread_rwlock_timedwrlock(3),  and
              sem_timedwait(3)).

              Timer slack is not applied to threads that are scheduled under a real-time scheduling policy  (see
              sched_setscheduler(2)).

              When  a new thread is created, the two timer slack values are made the same as the "current" value
              of the creating thread.  Thereafter, a thread can adjust  its  "current"  timer  slack  value  via
              PR_SET_TIMERSLACK.  The "default" value can't be changed.  The timer slack values of init (PID 1),
              the ancestor of all processes, are 50,000 nanoseconds (50 microseconds).  The timer slack value is
              inherited by a child created via fork(2), and is preserved across execve(2).

              Since  Linux  4.6,  the "current" timer slack value of any process can be examined and changed via
              the file /proc/pid/timerslack_ns.  See proc(5).

       PR_GET_TIMERSLACK (since Linux 2.6.28)
              Return (as the function result) the "current" timer slack value of the calling thread.

       PR_SET_TIMING (since Linux 2.6.0)
              Set whether to use (normal, traditional) statistical process timing  or  accurate  timestamp-based
              process    timing,    by   passing   PR_TIMING_STATISTICAL   or   PR_TIMING_TIMESTAMP   to   arg2.
              PR_TIMING_TIMESTAMP is not currently implemented (attempting to set this mode will yield the error
              EINVAL).

       PR_GET_TIMING (since Linux 2.6.0)
              Return (as the function result) which process timing method is currently in use.

       PR_SET_TSC (since Linux 2.6.26, x86 only)
              Set  the  state  of the flag determining whether the timestamp counter can be read by the process.
              Pass PR_TSC_ENABLE to arg2 to allow it to be read, or PR_TSC_SIGSEGV to generate  a  SIGSEGV  when
              the process tries to read the timestamp counter.

       PR_GET_TSC (since Linux 2.6.26, x86 only)
              Return  the  state  of  the  flag  determining  whether  the timestamp counter can be read, in the
              location pointed to by (int *) arg2.

       PR_SET_UNALIGN
              (Only on: ia64, since Linux 2.3.48; parisc, since  Linux  2.6.15;  PowerPC,  since  Linux  2.6.18;
              Alpha,  since  Linux  2.6.22; sh, since Linux 2.6.34; tile, since Linux 3.12) Set unaligned access
              control bits to arg2.  Pass PR_UNALIGN_NOPRINT to silently fix  up  unaligned  user  accesses,  or
              PR_UNALIGN_SIGBUS  to generate SIGBUS on unaligned user access.  Alpha also supports an additional
              flag with the value of 4 and no corresponding named constant, which instructs kernel to not fix up
              unaligned  accesses  (it  is analogous to providing the UAC_NOFIX flag in SSI_NVPAIRS operation of
              the setsysinfo() system call on Tru64).

       PR_GET_UNALIGN
              (See PR_SET_UNALIGN for information on  versions  and  architectures.)   Return  unaligned  access
              control bits, in the location pointed to by (unsigned int *) arg2.

       PR_GET_AUXV (since Linux 6.4)
              Get the auxiliary vector (auxv) into the buffer pointed to by (void *) arg2, whose length is given
              by arg3.  If the buffer is not long enough for  the  full  auxiliary  vector,  the  copy  will  be
              truncated.   Return  (as  the  function result) the full length of the auxiliary vector.  arg4 and
              arg5 must be 0.

       PR_SET_MDWE (since Linux 6.3)
              Set the calling process' Memory-Deny-Write-Execute protection mask.  Once protection bits are set,
              they can not be changed.  arg2 must be a bit mask of:

              PR_MDWE_REFUSE_EXEC_GAIN
                     New  memory  mapping protections can't be writable and executable.  Non-executable mappings
                     can't become executable.

              PR_MDWE_NO_INHERIT  (since Linux 6.6)
                     Do not propagate MDWE protection to child processes on fork(2).  Setting this bit  requires
                     setting PR_MDWE_REFUSE_EXEC_GAIN too.

       PR_GET_MDWE (since Linux 6.3)
              Return  (as  the  function  result)  the  Memory-Deny-Write-Execute protection mask of the calling
              process.  (See PR_SET_MDWE for information on the protection mask bits.)

RETURN VALUE

       On  success,  PR_CAP_AMBIENT+PR_CAP_AMBIENT_IS_SET,  PR_CAPBSET_READ,  PR_GET_DUMPABLE,   PR_GET_FP_MODE,
       PR_GET_IO_FLUSHER,     PR_GET_KEEPCAPS,    PR_MCE_KILL_GET,    PR_GET_NO_NEW_PRIVS,    PR_GET_SECUREBITS,
       PR_GET_SPECULATION_CTRL,  PR_SVE_GET_VL,  PR_SVE_SET_VL,   PR_GET_TAGGED_ADDR_CTRL,   PR_GET_THP_DISABLE,
       PR_GET_TIMING,  PR_GET_TIMERSLACK, PR_GET_AUXV, and (if it returns) PR_GET_SECCOMP return the nonnegative
       values described above.  All other op values return 0 on success.  On error, -1 is returned, and errno is
       set to indicate the error.

ERRORS

       EACCES op  is  PR_SET_SECCOMP  and  arg2  is  SECCOMP_MODE_FILTER,  but  the  process  does  not have the
              CAP_SYS_ADMIN capability or has  not  set  the  no_new_privs  attribute  (see  the  discussion  of
              PR_SET_NO_NEW_PRIVS above).

       EACCES op is PR_SET_MM, and arg3 is PR_SET_MM_EXE_FILE, the file is not executable.

       EBADF  op is PR_SET_MM, arg3 is PR_SET_MM_EXE_FILE, and the file descriptor passed in arg4 is not valid.

       EBUSY  op  is  PR_SET_MM,  arg3  is  PR_SET_MM_EXE_FILE,  and  this  the  second  attempt  to  change the
              /proc/pid/exe symbolic link, which is prohibited.

       EFAULT arg2 is an invalid address.

       EFAULT op   is   PR_SET_SECCOMP,   arg2   is   SECCOMP_MODE_FILTER,   the   system   was    built    with
              CONFIG_SECCOMP_FILTER, and arg3 is an invalid address.

       EFAULT op is PR_SET_SYSCALL_USER_DISPATCH and arg5 has an invalid address.

       EINVAL The value of op is not recognized, or not supported on this system.

       EINVAL op is PR_MCE_KILL or PR_MCE_KILL_GET or PR_SET_MM, and unused prctl() arguments were not specified
              as zero.

       EINVAL arg2 is not valid value for this op.

       EINVAL op is PR_SET_SECCOMP or PR_GET_SECCOMP, and the kernel was not configured with CONFIG_SECCOMP.

       EINVAL op is PR_SET_SECCOMP, arg2  is  SECCOMP_MODE_FILTER,  and  the  kernel  was  not  configured  with
              CONFIG_SECCOMP_FILTER.

       EINVAL op is PR_SET_MM, and one of the following is true

              •  arg4 or arg5 is nonzero;

              •  arg3  is  greater  than  TASK_SIZE  (the  limit  on the size of the user address space for this
                 architecture);

              •  arg2 is PR_SET_MM_START_CODE, PR_SET_MM_END_CODE, PR_SET_MM_START_DATA, PR_SET_MM_END_DATA,  or
                 PR_SET_MM_START_STACK,  and  the  permissions  of  the  corresponding  memory  area  are not as
                 required;

              •  arg2 is PR_SET_MM_START_BRK or PR_SET_MM_BRK, and arg3 is less than or equal to the end of  the
                 data  segment  or  specifies  a  value  that  would  cause the RLIMIT_DATA resource limit to be
                 exceeded.

       EINVAL op is PR_SET_PTRACER and arg2 is not 0, PR_SET_PTRACER_ANY, or the PID of an existing process.

       EINVAL op is PR_SET_PDEATHSIG and arg2 is not a valid signal number.

       EINVAL op is PR_SET_DUMPABLE and arg2 is neither SUID_DUMP_DISABLE nor SUID_DUMP_USER.

       EINVAL op is PR_SET_TIMING and arg2 is not PR_TIMING_STATISTICAL.

       EINVAL op is PR_SET_NO_NEW_PRIVS and arg2 is not equal to 1 or arg3, arg4, or arg5 is nonzero.

       EINVAL op is PR_GET_NO_NEW_PRIVS and arg2, arg3, arg4, or arg5 is nonzero.

       EINVAL op is PR_SET_THP_DISABLE and arg3, arg4, or arg5 is nonzero.

       EINVAL op is PR_GET_THP_DISABLE and arg2, arg3, arg4, or arg5 is nonzero.

       EINVAL op  is  PR_CAP_AMBIENT  and   an   unused   argument   (arg4,   arg5,   or,   in   the   case   of
              PR_CAP_AMBIENT_CLEAR_ALL,   arg3)   is  nonzero;  or  arg2  has  an  invalid  value;  or  arg2  is
              PR_CAP_AMBIENT_LOWER, PR_CAP_AMBIENT_RAISE, or PR_CAP_AMBIENT_IS_SET and arg3 does not  specify  a
              valid capability.

       EINVAL op  was PR_GET_SPECULATION_CTRL or PR_SET_SPECULATION_CTRL and unused arguments to prctl() are not
              0.

       EINVAL op is PR_PAC_RESET_KEYS and the arguments are invalid or  unsupported.   See  the  description  of
              PR_PAC_RESET_KEYS above for details.

       EINVAL op  is PR_SVE_SET_VL and the arguments are invalid or unsupported, or SVE is not available on this
              platform.  See the description of PR_SVE_SET_VL above for details.

       EINVAL op is PR_SVE_GET_VL and SVE is not available on this platform.

       EINVAL op is PR_SET_SYSCALL_USER_DISPATCH and one of the following is true:

              •  arg2 is PR_SYS_DISPATCH_OFF and the remaining arguments are not 0;

              •  arg2 is PR_SYS_DISPATCH_ON and the memory range specified is outside the address space  of  the
                 process.

              •  arg2 is invalid.

       EINVAL op  is  PR_SET_TAGGED_ADDR_CTRL and the arguments are invalid or unsupported.  See the description
              of PR_SET_TAGGED_ADDR_CTRL above for details.

       EINVAL op is PR_GET_TAGGED_ADDR_CTRL and the arguments are invalid or unsupported.  See  the  description
              of PR_GET_TAGGED_ADDR_CTRL above for details.

       ENODEV op  was  PR_SET_SPECULATION_CTRL  the  kernel  or  CPU  does not support the requested speculation
              misfeature.

       ENXIO  op was PR_MPX_ENABLE_MANAGEMENT or PR_MPX_DISABLE_MANAGEMENT and the kernel or the  CPU  does  not
              support MPX management.  Check that the kernel and processor have MPX support.

       ENXIO  op  was PR_SET_SPECULATION_CTRL implies that the control of the selected speculation misfeature is
              not possible.  See PR_GET_SPECULATION_CTRL for  the  bit  fields  to  determine  which  option  is
              available.

       EOPNOTSUPP
              op is PR_SET_FP_MODE and arg2 has an invalid or unsupported value.

       EPERM  op  is  PR_SET_SECUREBITS,  and  the  caller does not have the CAP_SETPCAP capability, or tried to
              unset a "locked" flag, or tried to set a  flag  whose  corresponding  locked  flag  was  set  (see
              capabilities(7)).

       EPERM  op  is PR_SET_SPECULATION_CTRL wherein the speculation was disabled with PR_SPEC_FORCE_DISABLE and
              caller tried to enable it again.

       EPERM  op is PR_SET_KEEPCAPS, and the caller's SECBIT_KEEP_CAPS_LOCKED flag is set (see capabilities(7)).

       EPERM  op is PR_CAPBSET_DROP, and the caller does not have the CAP_SETPCAP capability.

       EPERM  op is PR_SET_MM, and the caller does not have the CAP_SYS_RESOURCE capability.

       EPERM  op is PR_CAP_AMBIENT and arg2 is PR_CAP_AMBIENT_RAISE, but either the capability specified in arg3
              is   not   present   in   the   process's  permitted  and  inheritable  capability  sets,  or  the
              PR_CAP_AMBIENT_LOWER securebit has been set.

       ERANGE op   was   PR_SET_SPECULATION_CTRL   and   arg3   is    not    PR_SPEC_ENABLE,    PR_SPEC_DISABLE,
              PR_SPEC_FORCE_DISABLE, nor PR_SPEC_DISABLE_NOEXEC.

VERSIONS

       IRIX  has a prctl() system call (also introduced in Linux 2.1.44 as irix_prctl on the MIPS architecture),
       with prototype

           ptrdiff_t prctl(int op, int arg2, int arg3);

       and operations to get the maximum number of processes per user, get the maximum number of processors  the
       calling  process  can  use,  find  out  whether  a specified process is currently blocked, get or set the
       maximum stack size, and so on.

STANDARDS

       Linux.

HISTORY

       Linux 2.1.57, glibc 2.0.6

SEE ALSO

       signal(2), core(5)