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, 17 insertions, 0 deletions

diff --git a/Documentation/security/lsm-development.rst b/Documentation/security/lsm-development.rst
new file mode 100644
index 000000000..5895e529d
--- /dev/null
+++ b/Documentation/security/lsm-development.rst
@@ -0,0 +1,17 @@
+=================================
+Linux Security Module Development
+=================================
+
+Based on https://lore.kernel.org/r/20071026073721.618b4778@laptopd505.fenrus.org,
+a new LSM is accepted into the kernel when its intent (a description of
+what it tries to protect against and in what cases one would expect to
+use it) has been appropriately documented in ``Documentation/admin-guide/LSM/``.
+This allows an LSM's code to be easily compared to its goals, and so
+that end users and distros can make a more informed decision about which
+LSMs suit their requirements.
+
+For extensive documentation on the available LSM hook interfaces, please
+see ``security/security.c`` and associated structures:
+
+.. kernel-doc:: security/security.c
+   :export: