1pkey_alloc(2) System Calls Manual pkey_alloc(2)
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6 pkey_alloc, pkey_free - allocate or free a protection key
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9 Standard C library (libc, -lc)
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12 #define _GNU_SOURCE /* See feature_test_macros(7) */
13 #include <sys/mman.h>
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15 int pkey_alloc(unsigned int flags, unsigned int access_rights);
16 int pkey_free(int pkey);
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19 pkey_alloc() allocates a protection key (pkey) and allows it to be
20 passed to pkey_mprotect(2).
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22 The pkey_alloc() flags is reserved for future use and currently must
23 always be specified as 0.
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25 The pkey_alloc() access_rights argument may contain zero or more dis‐
26 able operations:
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28 PKEY_DISABLE_ACCESS
29 Disable all data access to memory covered by the returned pro‐
30 tection key.
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32 PKEY_DISABLE_WRITE
33 Disable write access to memory covered by the returned protec‐
34 tion key.
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36 pkey_free() frees a protection key and makes it available for later al‐
37 locations. After a protection key has been freed, it may no longer be
38 used in any protection-key-related operations.
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40 An application should not call pkey_free() on any protection key which
41 has been assigned to an address range by pkey_mprotect(2) and which is
42 still in use. The behavior in this case is undefined and may result in
43 an error.
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46 On success, pkey_alloc() returns a positive protection key value. On
47 success, pkey_free() returns zero. On error, -1 is returned, and errno
48 is set to indicate the error.
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51 EINVAL pkey, flags, or access_rights is invalid.
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53 ENOSPC (pkey_alloc()) All protection keys available for the current
54 process have been allocated. The number of keys available is
55 architecture-specific and implementation-specific and may be re‐
56 duced by kernel-internal use of certain keys. There are cur‐
57 rently 15 keys available to user programs on x86.
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59 This error will also be returned if the processor or operating
60 system does not support protection keys. Applications should
61 always be prepared to handle this error, since factors outside
62 of the application's control can reduce the number of available
63 pkeys.
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66 Linux.
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69 Linux 4.9, glibc 2.27.
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72 pkey_alloc() is always safe to call regardless of whether or not the
73 operating system supports protection keys. It can be used in lieu of
74 any other mechanism for detecting pkey support and will simply fail
75 with the error ENOSPC if the operating system has no pkey support.
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77 The kernel guarantees that the contents of the hardware rights register
78 (PKRU) will be preserved only for allocated protection keys. Any time
79 a key is unallocated (either before the first call returning that key
80 from pkey_alloc() or after it is freed via pkey_free()), the kernel may
81 make arbitrary changes to the parts of the rights register affecting
82 access to that key.
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85 See pkeys(7).
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88 pkey_mprotect(2), pkeys(7)
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92Linux man-pages 6.04 2023-03-30 pkey_alloc(2)