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authorChangbin Du <changbin.du@gmail.com>2019-05-08 15:21:26 (GMT)
committerJonathan Corbet <corbet@lwn.net>2019-05-08 20:34:10 (GMT)
commit28e21eac94a2ee2512ae6c21f04a0b41fb26cb0b (patch)
tree454cf1033cb288d76f32edad35103434155a5b8f /Documentation/x86
parent2f6eae4730120fd6459f55e47b750cd3570e9349 (diff)
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Documentation: x86: convert protection-keys.txt to reST
This converts the plain text documentation to reStructuredText format and add it to Sphinx TOC tree. No essential content change. Signed-off-by: Changbin Du <changbin.du@gmail.com> Reviewed-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Diffstat (limited to 'Documentation/x86')
-rw-r--r--Documentation/x86/index.rst1
-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 f7012e4..e2c0db9 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 ecb0d2d..49d9833 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);