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, 13 insertions, 0 deletions

diff --git a/scripts/xen-hypercalls.sh b/scripts/xen-hypercalls.sh
new file mode 100755
index 000000000..f18b00843
--- /dev/null
+++ b/scripts/xen-hypercalls.sh
@@ -0,0 +1,13 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+out="$1"
+shift
+in="$@"
+
+for i in $in; do
+	eval $CPP $LINUXINCLUDE -dD -imacros "$i" -x c /dev/null
+done | \
+awk '$1 == "#define" && $2 ~ /__HYPERVISOR_[a-z][a-z_0-9]*/ { v[$3] = $2 }
+	END {   print "/* auto-generated by scripts/xen-hypercall.sh */"
+		for (i in v) if (!(v[i] in v))
+			print "HYPERCALL("substr(v[i], 14)")"}' | sort -u >$out