diff options
Diffstat (limited to 'Documentation/x86')
| -rw-r--r-- | Documentation/x86/index.rst | 1 | ||||
| -rw-r--r-- | Documentation/x86/protection-keys.rst (renamed from Documentation/x86/protection-keys.txt) | 33 |
2 files changed, 22 insertions, 12 deletions
diff --git a/Documentation/x86/index.rst b/Documentation/x86/index.rst index f7012e4afacd..e2c0db9fcd4e 100644 --- a/Documentation/x86/index.rst +++ b/Documentation/x86/index.rst @@ -18,3 +18,4 @@ x86-specific Documentation tlb mtrr pat + protection-keys diff --git a/Documentation/x86/protection-keys.txt b/Documentation/x86/protection-keys.rst index ecb0d2dadfb7..49d9833af871 100644 --- a/Documentation/x86/protection-keys.txt +++ b/Documentation/x86/protection-keys.rst @@ -1,3 +1,9 @@ +.. SPDX-License-Identifier: GPL-2.0 + +====================== +Memory Protection Keys +====================== + Memory Protection Keys for Userspace (PKU aka PKEYs) is a feature which is found on Intel's Skylake "Scalable Processor" Server CPUs. It will be avalable in future non-server parts. @@ -23,9 +29,10 @@ even though there is theoretically space in the PAE PTEs. These permissions are enforced on data access only and have no effect on instruction fetches. -=========================== Syscalls =========================== +Syscalls +======== -There are 3 system calls which directly interact with pkeys: +There are 3 system calls which directly interact with pkeys:: int pkey_alloc(unsigned long flags, unsigned long init_access_rights) int pkey_free(int pkey); @@ -37,6 +44,7 @@ pkey_alloc(). An application calls the WRPKRU instruction directly in order to change access permissions to memory covered with a key. In this example WRPKRU is wrapped by a C function called pkey_set(). +:: int real_prot = PROT_READ|PROT_WRITE; pkey = pkey_alloc(0, PKEY_DISABLE_WRITE); @@ -45,43 +53,44 @@ called pkey_set(). ... application runs here Now, if the application needs to update the data at 'ptr', it can -gain access, do the update, then remove its write access: +gain access, do the update, then remove its write access:: pkey_set(pkey, 0); // clear PKEY_DISABLE_WRITE *ptr = foo; // assign something pkey_set(pkey, PKEY_DISABLE_WRITE); // set PKEY_DISABLE_WRITE again Now when it frees the memory, it will also free the pkey since it -is no longer in use: +is no longer in use:: munmap(ptr, PAGE_SIZE); pkey_free(pkey); -(Note: pkey_set() is a wrapper for the RDPKRU and WRPKRU instructions. - An example implementation can be found in - tools/testing/selftests/x86/protection_keys.c) +.. note:: pkey_set() is a wrapper for the RDPKRU and WRPKRU instructions. + An example implementation can be found in + tools/testing/selftests/x86/protection_keys.c. -=========================== Behavior =========================== +Behavior +======== The kernel attempts to make protection keys consistent with the -behavior of a plain mprotect(). For instance if you do this: +behavior of a plain mprotect(). For instance if you do this:: mprotect(ptr, size, PROT_NONE); something(ptr); -you can expect the same effects with protection keys when doing this: +you can expect the same effects with protection keys when doing this:: pkey = pkey_alloc(0, PKEY_DISABLE_WRITE | PKEY_DISABLE_READ); pkey_mprotect(ptr, size, PROT_READ|PROT_WRITE, pkey); something(ptr); That should be true whether something() is a direct access to 'ptr' -like: +like:: *ptr = foo; or when the kernel does the access on the application's behalf like -with a read(): +with a read():: read(fd, ptr, 1); |