openrisc: fix arbitrary kernel memory access via or1k_atomic syscallgrafted

sys_or1k_atomic() (syscall 244 in the "or1k" ABI) takes two user
pointers, v1 and v2, and swaps the words they point to in hand-written
assembly.

    l.lwz   r29,0(r4)
    l.lwz   r27,0(r5)
    l.sw    0(r4),r27
    l.sw    0(r5),r29

The pointers are not checked with access_ok(). The four memory
accesses also have no exception table entries.

A caller passes a kernel address as either pointer, and the syscall
reads from and writes to it directly.

This gives an unprivileged process a kernel read/write primitive. It
overwrites kernel data such as the sys_call_table, gaining code
execution in kernel context.

Check both pointers before entering the critical section. Add fixups
for the four memory accesses so faults on valid but unmapped user
addresses return -EFAULT.

[shorne@gmail.com: fix comment style]
Fixes: 9d02a4283e9c ("OpenRISC: Boot code")
Cc: stable@vger.kernel.org
Signed-off-by: Ali Ahmet Memis <ali@iusegentoo.com>
Signed-off-by: Stafford Horne <shorne@gmail.com>

1 files changed, 30 insertions, 0 deletions

diff --git a/Documentation/maintainer/configure-git.rst b/Documentation/maintainer/configure-git.rst
new file mode 100644
index 000000000..0c21f203c
--- /dev/null
+++ b/Documentation/maintainer/configure-git.rst
@@ -0,0 +1,30 @@
+Configuring Git
+===============
+
+This chapter describes maintainer level git configuration.
+
+Tagged branches used in pull requests (see
+Documentation/maintainer/pull-requests.rst) should be signed with the
+developers public GPG key. Signed tags can be created by passing
+``-u <key-id>`` to ``git tag``. However, since you would *usually* use the same
+key for the project, you can set it in the configuration and use the ``-s``
+flag. To set the default ``key-id`` use::
+
+	git config user.signingkey "keyname"
+
+Alternatively, edit your ``.git/config`` or ``~/.gitconfig`` file by hand::
+
+	[user]
+		name = Jane Developer
+		email = jd@domain.org
+		signingkey = jd@domain.org
+
+You may need to tell ``git`` to use ``gpg2``::
+
+	[gpg]
+		program = /path/to/gpg2
+
+You may also like to tell ``gpg`` which ``tty`` to use (add to your shell
+rc file)::
+
+	export GPG_TTY=$(tty)