plucky (2) PR_MPX_ENABLE_MANAGEMENT.2.gz

NAME

       PR_MPX_ENABLE_MANAGEMENT,  PR_MPX_DISABLE_MANAGEMENT  -  enable  or  disable  kernel management of Memory
       Protection eXtensions (MPX)

LIBRARY

       Standard C library (libc, -lc)

SYNOPSIS

       #include <linux/prctl.h>  /* Definition of PR_* constants */
       #include <sys/prctl.h>

       [[deprecated]] int prctl(PR_MPX_ENABLE_MANAGEMENT, 0L, 0L, 0L, 0L);
       [[deprecated]] int prctl(PR_MPX_DISABLE_MANAGEMENT, 0L, 0L, 0L, 0L);

DESCRIPTION

       Enable or disable kernel management of Memory Protection eXtensions (MPX) bounds tables.

       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.

RETURN VALUE

       On success, 0 is returned.  On error, -1 is returned, and errno is set to indicate the error.

ERRORS

       ENXIO  The kernel or the CPU does not support MPX management.  Check that the kernel and  processor  have
              MPX support.

STANDARDS

       None.

HISTORY

       Linux 3.19.  Removed in Linux 5.4.  Only on x86.

       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.

SEE ALSO

       prctl(2)

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