pkey_alloc(2) - Linux manual page (original) (raw)

pkeyalloc(2) System Calls Manual pkeyalloc(2)

NAME top

   pkey_alloc, pkey_free - allocate or free a protection key

LIBRARY top

   Standard C library (_libc_, _-lc_)

SYNOPSIS top

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

   **int pkey_alloc(unsigned int** _flags_**, unsigned int** _accessrights_**);**
   **int pkey_free(int** _pkey_**);**

DESCRIPTION top

   **pkey_alloc**() allocates a protection key (pkey) and allows it to be
   passed to [pkey_mprotect(2)](../man2/pkey%5Fmprotect.2.html).

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

   The **pkey_alloc**() _accessrights_ 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)](../man2/pkey%5Fmprotect.2.html)
   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](../man3/errno.3.html)_ is set to indicate the error.

ERRORS top

   **EINVAL** _pkey_, _flags_, or _accessrights_ 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.

STANDARDS top

   Linux.

HISTORY top

   Linux 4.9, glibc 2.27.

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)](../man7/pkeys.7.html).

SEE ALSO top

   [pkey_mprotect(2)](../man2/pkey%5Fmprotect.2.html), [pkeys(7)](../man7/pkeys.7.html)

COLOPHON top

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Linux man-pages 6.10 2024-07-23 pkeyalloc(2)

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