Linux: Implement interfaces for memory protection keys

This adds system call wrappers for pkey_alloc, pkey_free, pkey_mprotect,
and x86-64 implementations of pkey_get and pkey_set, which abstract over
the PKRU CPU register and hide the actual number of memory protection
keys supported by the CPU.  pkey_mprotect with a -1 key is implemented
using mprotect, so it will work even if the kernel does not support the
pkey_mprotect system call.

The system call wrapers use unsigned int instead of unsigned long for
parameters, so that no special treatment for x32 is needed.  The flags
argument is currently unused, and the access rights bit mask is limited
to two bits by the current PKRU register layout anyway.

Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>

1 files changed, 28 insertions, 0 deletions

diff --git a/sysdeps/unix/sysv/linux/bits/mman-shared.h b/sysdeps/unix/sysv/linux/bits/mman-shared.h
index bee99c2384..9e532adb23 100644
--- a/sysdeps/unix/sysv/linux/bits/mman-shared.h
+++ b/sysdeps/unix/sysv/linux/bits/mman-shared.h
@@ -33,6 +33,12 @@
 #  define MLOCK_ONFAULT 1U
 # endif
 
+/* Access rights for pkey_alloc.  */
+# ifndef PKEY_DISABLE_ACCESS
+#  define PKEY_DISABLE_ACCESS 0x1
+#  define PKEY_DISABLE_WRITE 0x2
+# endif
+
 __BEGIN_DECLS
 
 /* Create a new memory file descriptor.  NAME is a name for debugging.
@@ -43,6 +49,28 @@ int memfd_create (const char *__name, unsigned int __flags) __THROW;
    memory.  FLAGS is a combination of the MLOCK_* flags above.  */
 int mlock2 (const void *__addr, size_t __length, unsigned int __flags) __THROW;
 
+/* Allocate a new protection key, with the PKEY_DISABLE_* bits
+   specified in ACCESS_RIGHTS.  The protection key mask for the
+   current thread is updated to match the access privilege for the new
+   key.  */
+int pkey_alloc (unsigned int __flags, unsigned int __access_rights) __THROW;
+
+/* Update the access rights for the current thread for KEY, which must
+   have been allocated using pkey_alloc.  */
+int pkey_set (int __key, unsigned int __access_rights) __THROW;
+
+/* Return the access rights for the current thread for KEY, which must
+   have been allocated using pkey_alloc.  */
+int pkey_get (int _key) __THROW;
+
+/* Free an allocated protection key, which must have been allocated
+   using pkey_alloc.  */
+int pkey_free (int __key) __THROW;
+
+/* Apply memory protection flags for KEY to the specified address
+   range.  */
+int pkey_mprotect (void *__addr, size_t __len, int __prot, int __pkey) __THROW;
+
 __END_DECLS
 
 #endif /* __USE_GNU */