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, 32 insertions, 0 deletions

diff --git a/scripts/depmod.sh b/scripts/depmod.sh
new file mode 100755
index 000000000..3c34fecac
--- /dev/null
+++ b/scripts/depmod.sh
@@ -0,0 +1,32 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+#
+# A depmod wrapper
+
+if test $# -ne 1; then
+	echo "Usage: $0 <kernelrelease>" >&2
+	exit 1
+fi
+
+KERNELRELEASE=$1
+
+: ${DEPMOD:=depmod}
+
+if ! test -r "${objtree}/System.map" ; then
+	echo "Warning: modules_install: missing 'System.map' file. Skipping depmod." >&2
+	exit 0
+fi
+
+# legacy behavior: "depmod" in /sbin, no /sbin in PATH
+PATH="$PATH:/sbin"
+if [ -z $(command -v $DEPMOD) ]; then
+	echo "Warning: 'make modules_install' requires $DEPMOD. Please install it." >&2
+	echo "This is probably in the kmod package." >&2
+	exit 0
+fi
+
+set -- -ae -F "${objtree}/System.map"
+if test -n "$INSTALL_MOD_PATH"; then
+	set -- "$@" -b "$INSTALL_MOD_PATH"
+fi
+exec "$DEPMOD" "$@" "$KERNELRELEASE"