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, 21 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/debugfs-ec b/Documentation/ABI/testing/debugfs-ec
new file mode 100644
index 000000000..ab6099daa
--- /dev/null
+++ b/Documentation/ABI/testing/debugfs-ec
@@ -0,0 +1,21 @@
+What:		/sys/kernel/debug/ec/*/{gpe,use_global_lock,io}
+Date:		July 2010
+Contact:	Thomas Renninger <trenn@suse.de>
+Description:
+
+General information like which GPE is assigned to the EC and whether
+the global lock should get used.
+Knowing the EC GPE one can watch the amount of HW events related to
+the EC here (XY -> GPE number from `/sys/kernel/debug/ec/*/gpe`):
+/sys/firmware/acpi/interrupts/gpeXY
+
+The io file is binary and a userspace tool located here:
+ftp://ftp.suse.com/pub/people/trenn/sources/ec/
+should get used to read out the 256 Embedded Controller registers
+or writing to them.
+
+CAUTION:
+  Do not write to the Embedded Controller if you don't know
+  what you are doing! Rebooting afterwards also is a good idea.
+  This can influence the way your machine is cooled and fans may
+  not get switched on again after you did a wrong write.