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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | NOTES | EXAMPLE | 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
#include <sys/mman.h>
int pkey_alloc(unsigned long flags, unsigned long 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 4.15 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 2018-02-02 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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HTML rendering created 2018-02-02 by Michael Kerrisk, author of The Linux Programming Interface, maintainer of the Linux man-pages project. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH.
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