Section: Linux Programmer's Manual (2)
pkey_alloc, pkey_free - allocate or free a protection key
#define _GNU_SOURCE /* See feature_test_macros(7) */
int pkey_alloc(unsigned int flags, unsigned int access_rights);
int pkey_free(int pkey);
allocates a protection key (pkey) and allows it to be passed to
is reserved for future use and currently must always be specified as 0.
argument may contain zero or more disable operations:
Disable all data access to memory covered by the returned protection key.
Disable write access to memory covered by the returned protection key.
frees a protection key and makes it available for later
After a protection key has been freed, it may no longer be used
in any protection-key-related operations.
An application should not call
on any protection key which has been assigned to an address
and which is still in use.
The behavior in this case is undefined and may result in an error.
returns a positive protection key value.
On error, -1 is returned, and
is set appropriately.
All protection keys available for the current process have
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.
were added to Linux in kernel 4.9;
library support was added in glibc 2.27.
system calls are Linux-specific.
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
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
Any time a key is unallocated (either before the first call
returning that key from
or after it is freed via
the kernel may make arbitrary changes to the parts of the
rights register affecting access to that key.
This page is part of release 5.04 of the Linux
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