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, 27 insertions, 0 deletions

diff --git a/scripts/mkcompile_h b/scripts/mkcompile_h
new file mode 100755
index 000000000..2596f78e5
--- /dev/null
+++ b/scripts/mkcompile_h
@@ -0,0 +1,27 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+
+UTS_MACHINE=$1
+CC_VERSION="$2"
+LD=$3
+
+if test -z "$KBUILD_BUILD_USER"; then
+	LINUX_COMPILE_BY=$(whoami | sed 's/\\/\\\\/')
+else
+	LINUX_COMPILE_BY=$KBUILD_BUILD_USER
+fi
+if test -z "$KBUILD_BUILD_HOST"; then
+	LINUX_COMPILE_HOST=`uname -n`
+else
+	LINUX_COMPILE_HOST=$KBUILD_BUILD_HOST
+fi
+
+LD_VERSION=$(LC_ALL=C $LD -v | head -n1 |
+		sed -e 's/(compatible with [^)]*)//' -e 's/[[:space:]]*$//')
+
+cat <<EOF
+#define UTS_MACHINE		"${UTS_MACHINE}"
+#define LINUX_COMPILE_BY	"${LINUX_COMPILE_BY}"
+#define LINUX_COMPILE_HOST	"${LINUX_COMPILE_HOST}"
+#define LINUX_COMPILER		"${CC_VERSION}, ${LD_VERSION}"
+EOF