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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | NOTES | EXAMPLES | SEE ALSO | COLOPHON |
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PKEY_ALLOC(2) Linux Programmer's Manual PKEY_ALLOC(2)
pkey_alloc, pkey_free - allocate or free a protection key
#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);
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.
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 appropriately.
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.
pkey_alloc() and pkey_free() were added to Linux in kernel 4.9;
library support was added in glibc 2.27.
The pkey_alloc() and pkey_free() system calls are Linux-specific.
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.
See pkeys(7).
pkey_mprotect(2), pkeys(7)
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/.
Linux 2020-06-09 PKEY_ALLOC(2)
Pages that refer to this page: mprotect(2), syscalls(2), pkeys(7)
Copyright and license for this manual page
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