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, 20 insertions, 0 deletions

diff --git a/scripts/mkuboot.sh b/scripts/mkuboot.sh
new file mode 100755
index 000000000..4b1fe09e9
--- /dev/null
+++ b/scripts/mkuboot.sh
@@ -0,0 +1,20 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+
+#
+# Build U-Boot image when `mkimage' tool is available.
+#
+
+MKIMAGE=$(type -path "${CROSS_COMPILE}mkimage")
+
+if [ -z "${MKIMAGE}" ]; then
+	MKIMAGE=$(type -path mkimage)
+	if [ -z "${MKIMAGE}" ]; then
+		# Doesn't exist
+		echo '"mkimage" command not found - U-Boot images will not be built' >&2
+		exit 1;
+	fi
+fi
+
+# Call "mkimage" to create U-Boot image
+${MKIMAGE} "$@"