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, 56 insertions, 0 deletions

diff --git a/tools/bootconfig/scripts/xbc.sh b/tools/bootconfig/scripts/xbc.sh
new file mode 100644
index 000000000..1f0ebf50d
--- /dev/null
+++ b/tools/bootconfig/scripts/xbc.sh
@@ -0,0 +1,56 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0-only
+
+# bootconfig utility functions
+
+XBC_TMPFILE=
+XBC_BASEDIR=`dirname $0`
+BOOTCONFIG=${BOOTCONFIG:=$XBC_BASEDIR/../bootconfig}
+if [ ! -x "$BOOTCONFIG" ]; then
+	BOOTCONFIG=`which bootconfig`
+	if [ -z "$BOOTCONFIG" ]; then
+		echo "Erorr: bootconfig command is not found" 1>&2
+		exit 1
+	fi
+fi
+
+xbc_cleanup() {
+	if [ "$XBC_TMPFILE" ]; then
+		rm -f "$XBC_TMPFILE"
+	fi
+}
+
+xbc_init() { # bootconfig-file
+	xbc_cleanup
+	XBC_TMPFILE=`mktemp bconf-XXXX`
+	trap xbc_cleanup EXIT TERM
+
+	$BOOTCONFIG -l $1 > $XBC_TMPFILE || exit 1
+}
+
+nr_args() { # args
+	echo $#
+}
+
+xbc_get_val() { # key [maxnum]
+	if [ "$2" ]; then
+		MAXOPT="-L $2"
+	fi
+	grep "^$1 =" $XBC_TMPFILE | cut -d= -f2- | \
+		sed -e 's/", /" /g' -e "s/',/' /g" | \
+		xargs $MAXOPT -n 1 echo
+}
+
+xbc_has_key() { # key
+	grep -q "^$1 =" $XBC_TMPFILE
+}
+
+xbc_has_branch() { # prefix-key
+	grep -q "^$1" $XBC_TMPFILE
+}
+
+xbc_subkeys() { # prefix-key depth [subkey-pattern]
+	__keys=`echo $1 | sed "s/\./ /g"`
+	__s=`nr_args $__keys`
+	grep "^$1$3" $XBC_TMPFILE | cut -d= -f1| cut -d. -f$((__s + 1))-$((__s + $2)) | uniq
+}