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, 14 insertions, 0 deletions

diff --git a/scripts/check-git b/scripts/check-git
new file mode 100755
index 000000000..2ca6c5df1
--- /dev/null
+++ b/scripts/check-git
@@ -0,0 +1,14 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# succeed if we are in a git repository
+
+srctree="$(dirname $0)/.."
+
+if ! git -C "${srctree}" rev-parse --verify HEAD >/dev/null 2>/dev/null; then
+	exit 1
+fi
+
+if ! test -z $(git -C "${srctree}" rev-parse --show-cdup 2>/dev/null); then
+	exit 1
+fi