pkey_alloc(2) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | NOTES | EXAMPLES | SEE ALSO | COLOPHON

PKEY_ALLOC(2)           Linux Programmer's Manual          PKEY_ALLOC(2)

NAME         top

       pkey_alloc, pkey_free - allocate or free a protection key

SYNOPSIS         top

       #define _GNU_SOURCE             /* See feature_test_macros(7) */
       #include <sys/mman.h>

       int pkey_alloc(unsigned int flags, unsigned int access_rights);
       int pkey_free(int pkey);

DESCRIPTION         top

       pkey_alloc() allocates a protection key (pkey) and allows it to
       be passed to pkey_mprotect(2).

       The pkey_alloc() flags is reserved for future use and currently
       must always be specified as 0.

       The pkey_alloc() access_rights argument may contain zero or more
       disable operations:

       PKEY_DISABLE_ACCESS
              Disable all data access to memory covered by the returned
              protection key.

       PKEY_DISABLE_WRITE
              Disable write access to memory covered by the returned
              protection key.

       pkey_free() frees a protection key and makes it available for
       later allocations.  After a protection key has been freed, it may
       no longer be used in any protection-key-related operations.

       An application should not call pkey_free() on any protection key
       which has been assigned to an address range by pkey_mprotect(2)
       and which is still in use.  The behavior in this case is
       undefined and may result in an error.

RETURN VALUE         top

       On success, pkey_alloc() returns a positive protection key value.
       On success, pkey_free() returns zero.  On error, -1 is returned,
       and errno is set to indicate the error.

ERRORS         top

       EINVAL pkey, flags, or access_rights is invalid.

       ENOSPC (pkey_alloc()) All protection keys available for the
              current process have been allocated.  The number of keys
              available is architecture-specific and implementation-
              specific and may be reduced by kernel-internal use of
              certain keys.  There are currently 15 keys available to
              user programs on x86.

              This error will also be returned if the processor or
              operating system does not support protection keys.
              Applications should always be prepared to handle this
              error, since factors outside of the application's control
              can reduce the number of available pkeys.

VERSIONS         top

       pkey_alloc() and pkey_free() were added to Linux in kernel 4.9;
       library support was added in glibc 2.27.

CONFORMING TO         top

       The pkey_alloc() and pkey_free() system calls are Linux-specific.

NOTES         top

       pkey_alloc() is always safe to call regardless of whether or not
       the operating system supports protection keys.  It can be used in
       lieu of any other mechanism for detecting pkey support and will
       simply fail with the error ENOSPC if the operating system has no
       pkey support.

       The kernel guarantees that the contents of the hardware rights
       register (PKRU) will be preserved only for allocated protection
       keys.  Any time a key is unallocated (either before the first
       call returning that key from pkey_alloc() or after it is freed
       via pkey_free()), the kernel may make arbitrary changes to the
       parts of the rights register affecting access to that key.

EXAMPLES         top

       See pkeys(7).

SEE ALSO         top

       pkey_mprotect(2), pkeys(7)

COLOPHON         top

       This page is part of release 5.11 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/.

Linux                          2021-03-22                  PKEY_ALLOC(2)

Pages that refer to this page: mprotect(2)syscalls(2)pkeys(7)