Section (2) pkey_alloc
pkey_alloc, pkey_free — allocate or free a protection key
#define _GNU_SOURCE /* See feature_test_macros(7) */ #include <sys/mman.h>
||unsigned int flags,|
|unsigned int access_rights
pkey_alloc() allocates a
protection key (pkey) and allows it to be passed to pkey_mprotect(2).
flags is reserved for future
use and currently must always be specified as 0.
access_rights 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.
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.
returns a positive protection key value. On success,
pkey_free() returns zero. On
error, −1 is returned, and
errno is set appropriately.
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_zsingle_quotesz_s control can reduce the number of available pkeys.
pkey_free() were added to Linux
in kernel 4.9; library support was added in glibc 2.27.
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.
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