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, 25 insertions, 0 deletions

diff --git a/arch/mips/Kbuild b/arch/mips/Kbuild
new file mode 100644
index 000000000..e901bf554
--- /dev/null
+++ b/arch/mips/Kbuild
@@ -0,0 +1,25 @@
+# SPDX-License-Identifier: GPL-2.0
+
+# platform specific definitions
+include $(srctree)/arch/mips/Kbuild.platforms
+obj-y := $(platform-y)
+
+# make clean traverses $(obj-) without having included .config, so
+# everything ends up here
+obj- := $(platform-y)
+
+# mips object files
+# The object files are linked as core-y files would be linked
+
+obj-y += generic/
+obj-y += kernel/
+obj-y += mm/
+obj-y += net/
+obj-y += vdso/
+
+ifdef CONFIG_KVM
+obj-y += kvm/
+endif
+
+# for cleaning
+subdir- += boot