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, 46 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/ppc-memtrace b/Documentation/ABI/testing/ppc-memtrace
new file mode 100644
index 000000000..9606aed33
--- /dev/null
+++ b/Documentation/ABI/testing/ppc-memtrace
@@ -0,0 +1,46 @@
+What:		/sys/kernel/debug/powerpc/memtrace
+Date:		Aug 2017
+KernelVersion:	4.14
+Contact:	linuxppc-dev@lists.ozlabs.org
+Description:	This folder contains the relevant debugfs files for the
+		hardware trace macro to use. CONFIG_PPC64_HARDWARE_TRACING
+		must be set.
+
+What:		/sys/kernel/debug/powerpc/memtrace/enable
+Date:		Aug 2017
+KernelVersion:	4.14
+Contact:	linuxppc-dev@lists.ozlabs.org
+Description:	Write an integer containing the size in bytes of the memory
+		you want removed from each NUMA node to this file - it must be
+		aligned to the memblock size. This amount of RAM will be removed
+		from each NUMA node in the kernel mappings and the following
+		debugfs files will be created. Once memory is successfully
+		removed from each node, the following files are created. To
+		re-add memory to the kernel, echo 0 into this file (it will be
+		automatically onlined).
+
+What:		/sys/kernel/debug/powerpc/memtrace/<node-id>
+Date:		Aug 2017
+KernelVersion:	4.14
+Contact:	linuxppc-dev@lists.ozlabs.org
+Description:	This directory contains information about the removed memory
+		from the specific NUMA node.
+
+What:		/sys/kernel/debug/powerpc/memtrace/<node-id>/size
+Date:		Aug 2017
+KernelVersion:	4.14
+Contact:	linuxppc-dev@lists.ozlabs.org
+Description:	This contains the size of the memory removed from the node.
+
+What:		/sys/kernel/debug/powerpc/memtrace/<node-id>/start
+Date:		Aug 2017
+KernelVersion:	4.14
+Contact:	linuxppc-dev@lists.ozlabs.org
+Description:	This contains the start address of the removed memory.
+
+What:		/sys/kernel/debug/powerpc/memtrace/<node-id>/trace
+Date:		Aug 2017
+KernelVersion:	4.14
+Contact:	linuxppc-dev@lists.ozlabs.org
+Description:	This is where the hardware trace macro will output the trace
+		it generates.