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, 7 insertions, 0 deletions

diff --git a/scripts/gen-randstruct-seed.sh b/scripts/gen-randstruct-seed.sh
new file mode 100755
index 000000000..61017b36c
--- /dev/null
+++ b/scripts/gen-randstruct-seed.sh
@@ -0,0 +1,7 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+
+SEED=$(od -A n -t x8 -N 32 /dev/urandom | tr -d ' \n')
+echo "$SEED" > "$1"
+HASH=$(echo -n "$SEED" | sha256sum | cut -d" " -f1)
+echo "#define RANDSTRUCT_HASHED_SEED \"$HASH\"" > "$2"