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, 69 insertions, 0 deletions

diff --git a/scripts/extract-ikconfig b/scripts/extract-ikconfig
new file mode 100755
index 000000000..8df33e7d6
--- /dev/null
+++ b/scripts/extract-ikconfig
@@ -0,0 +1,69 @@
+#!/bin/sh
+# ----------------------------------------------------------------------
+# extract-ikconfig - Extract the .config file from a kernel image
+#
+# This will only work when the kernel was compiled with CONFIG_IKCONFIG.
+#
+# The obscure use of the "tr" filter is to work around older versions of
+# "grep" that report the byte offset of the line instead of the pattern.
+#
+# (c) 2009,2010 Dick Streefland <dick@streefland.net>
+# Licensed under the terms of the GNU General Public License.
+# ----------------------------------------------------------------------
+
+cf1='IKCFG_ST\037\213\010'
+cf2='0123456789'
+
+dump_config()
+{
+	if	pos=`tr "$cf1\n$cf2" "\n$cf2=" < "$1" | grep -abo "^$cf2"`
+	then
+		pos=${pos%%:*}
+		tail -c+$(($pos+8)) "$1" | zcat > $tmp1 2> /dev/null
+		if	[ $? != 1 ]
+		then	# exit status must be 0 or 2 (trailing garbage warning)
+			cat $tmp1
+			exit 0
+		fi
+	fi
+}
+
+try_decompress()
+{
+	for	pos in `tr "$1\n$2" "\n$2=" < "$img" | grep -abo "^$2"`
+	do
+		pos=${pos%%:*}
+		tail -c+$pos "$img" | $3 > $tmp2 2> /dev/null
+		dump_config $tmp2
+	done
+}
+
+# Check invocation:
+me=${0##*/}
+img=$1
+if	[ $# -ne 1 -o ! -s "$img" ]
+then
+	echo "Usage: $me <kernel-image>" >&2
+	exit 2
+fi
+
+# Prepare temp files:
+tmp1=/tmp/ikconfig$$.1
+tmp2=/tmp/ikconfig$$.2
+trap "rm -f $tmp1 $tmp2" 0
+
+# Initial attempt for uncompressed images or objects:
+dump_config "$img"
+
+# That didn't work, so retry after decompression.
+try_decompress '\037\213\010' xy    gunzip
+try_decompress '\3757zXZ\000' abcde unxz
+try_decompress 'BZh'          xy    bunzip2
+try_decompress '\135\0\0\0'   xxx   unlzma
+try_decompress '\211\114\132' xy    'lzop -d'
+try_decompress '\002\041\114\030' xyy 'lz4 -d -l'
+try_decompress '\050\265\057\375' xxx unzstd
+
+# Bail out:
+echo "$me: Cannot find kernel config." >&2
+exit 1