1PKEY_ALLOC(2) Linux Programmer's Manual PKEY_ALLOC(2)
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6 pkey_alloc, pkey_free - allocate or free a protection key
7
9 #define _GNU_SOURCE /* See feature_test_macros(7) */
10 #include <sys/mman.h>
11 int pkey_alloc(unsigned int flags, unsigned int access_rights);
13 int pkey_free(int pkey);
14
16 pkey_alloc() allocates a protection key (pkey) and allows it to be
17 passed to pkey_mprotect(2).
18 The pkey_alloc() flags is reserved for future use and currently must
20 always be specified as 0.
21 The pkey_alloc() access_rights argument may contain zero or more dis‐
23 able operations:
24 PKEY_DISABLE_ACCESS
26 Disable all data access to memory covered by the returned pro‐
27 tection key.
28 PKEY_DISABLE_WRITE
30 Disable write access to memory covered by the returned protec‐
31 tion key.
32 pkey_free() frees a protection key and makes it available for later al‐
34 locations. After a protection key has been freed, it may no longer be
35 used in any protection-key-related operations.
36 An application should not call pkey_free() on any protection key which
38 has been assigned to an address range by pkey_mprotect(2) and which is
39 still in use. The behavior in this case is undefined and may result in
40 an error.
41
43 On success, pkey_alloc() returns a positive protection key value. On
44 success, pkey_free() returns zero. On error, -1 is returned, and errno
45 is set to indicate the error.
46
48 EINVAL pkey, flags, or access_rights is invalid.
49 ENOSPC (pkey_alloc()) All protection keys available for the current
51 process have been allocated. The number of keys available is
52 architecture-specific and implementation-specific and may be re‐
53 duced by kernel-internal use of certain keys. There are cur‐
54 rently 15 keys available to user programs on x86.
55 This error will also be returned if the processor or operating
57 system does not support protection keys. Applications should
58 always be prepared to handle this error, since factors outside
59 of the application's control can reduce the number of available
60 pkeys.
61
63 pkey_alloc() and pkey_free() were added to Linux in kernel 4.9; library
64 support was added in glibc 2.27.
65
67 The pkey_alloc() and pkey_free() system calls are Linux-specific.
68
70 pkey_alloc() is always safe to call regardless of whether or not the
71 operating system supports protection keys. It can be used in lieu of
72 any other mechanism for detecting pkey support and will simply fail
73 with the error ENOSPC if the operating system has no pkey support.
74 The kernel guarantees that the contents of the hardware rights register
76 (PKRU) will be preserved only for allocated protection keys. Any time
77 a key is unallocated (either before the first call returning that key
78 from pkey_alloc() or after it is freed via pkey_free()), the kernel may
79 make arbitrary changes to the parts of the rights register affecting
80 access to that key.
81
83 See pkeys(7).
84
86 pkey_mprotect(2), pkeys(7)
87
89 This page is part of release 5.12 of the Linux man-pages project. A
90 description of the project, information about reporting bugs, and the
91 latest version of this page, can be found at
92 https://www.kernel.org/doc/man-pages/.
93Linux 2021-03-22 PKEY_ALLOC(2)