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NAME

       prctl - operations on a process or thread

SYNOPSIS

       #include <sys/prctl.h>

       int prctl(int option, 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.

              In kernels up to and including 2.6.12, arg2 must be  either  0  (SUID_DUMP_DISABLE,
              process  is  not  dumpable)  or  1  (SUID_DUMP_USER, process is dumpable).  Between
              kernels 2.6.13 and 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 option 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_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.

              The  seccomp  mode  is  selected  via  arg2.  (The seccomp constants are defined in
              <linux/seccomp.h>.)

              With arg2 set to SECCOMP_MODE_STRICT, the only system  calls  that  the  thread  is
              permitted  to  make  are  read(2),  write(2), _exit(2) (but not exit_group(2)), and
              sigreturn(2).  Other system calls result in  the  delivery  of  a  SIGKILL  signal.
              Strict  secure  computing mode is useful for number-crunching applications that may
              need to execute untrusted byte code, perhaps obtained by reading  from  a  pipe  or
              socket.   This  operation  is  available  only  if  the  kernel  is configured with
              CONFIG_SECCOMP enabled.

              With arg2 set to SECCOMP_MODE_FILTER (since Linux 3.5), the  system  calls  allowed
              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.   This mode is available only if the kernel is
              configured with CONFIG_SECCOMP_FILTER enabled.

              If SECCOMP_MODE_FILTER filters permit fork(2), then the seccomp mode  is  inherited
              by children created by fork(2); if execve(2) is permitted, then the seccomp mode is
              preserved across execve(2).  If the filters permit prctl() calls,  then  additional
              filters  can  be  added;  they are run in order until the first non-allow result is
              seen.

              For     further     information,     see      the      kernel      source      file
              Documentation/userspace-api/seccomp_filter.rst                                  (or
              Documentation/prctl/seccomp_filter.txt before Linux 4.13).

       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().
              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_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.

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, and (if  it
       returns)  PR_GET_SECCOMP  return the nonnegative values described above.  All other option
       values return 0 on success.  On error, -1 is returned, and errno is set appropriately.

ERRORS

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

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

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

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

       EINVAL option 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 option.

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

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

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

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

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

       EINVAL option is PR_SET_TIMING and arg2 is not PR_TIMING_STATISTICAL.

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

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

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

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

       EINVAL option  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 option was PR_GET_SPECULATION_CTRL or PR_SET_SPECULATION_CTRL and unused  arguments
              to  prctl()  are  not  0.  EINVAL option is PR_PAC_RESET_KEYS and the arguments are
              invalid or  unsupported.   See  the  description  of  PR_PAC_RESET_KEYS  above  for
              details.

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

       EINVAL option  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 option 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 option was PR_SET_SPECULATION_CTRL the kernel or CPU does not support the requested
              speculation misfeature.

       ENXIO  option 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  option 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
              option is PR_SET_FP_MODE and arg2 has an invalid or unsupported value.

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

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

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

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

       EPERM  option  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 option 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

       The prctl() system call was introduced in Linux 2.1.57.

CONFORMING TO

       This  call  is  Linux-specific.   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 option, int arg2, int arg3);

       and options 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.

SEE ALSO

       signal(2), core(5)

COLOPHON

       This page is part of release 5.10 of the Linux man-pages project.  A  description  of  the
       project,  information  about  reporting  bugs, and the latest version of this page, can be
       found at https://www.kernel.org/doc/man-pages/.