[PATCH v4 48/63] Documentation: x86: convert protection-keys.txt to reST

Changbin Du
2019-04-23T16:29:17Z

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>
---
Documentation/x86/index.rst | 1 +
...rotection-keys.txt => protection-keys.rst} | 33 ++++++++++++-------
2 files changed, 22 insertions(+), 12 deletions(-)
rename Documentation/x86/{protection-keys.txt => protection-keys.rst} (83%)

diff --git a/Documentation/x86/index.rst b/Documentation/x86/index.rst
index e06b5c0ea883..576628b121cc 100644
--- a/Documentation/x86/index.rst
+++ b/Documentation/x86/index.rst
@@ -18,3 +18,4 @@ Linux x86 Support
tlb
mtrr
pat
+ protection-keys
diff --git a/Documentation/x86/protection-keys.txt b/Documentation/x86/protection-keys.rst
similarity index 83%
rename from Documentation/x86/protection-keys.txt
rename to 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);

--
2.20.1