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, 47 insertions, 0 deletions

diff --git a/arch/microblaze/lib/mulsi3.S b/arch/microblaze/lib/mulsi3.S
new file mode 100644
index 000000000..d6703a4d9
--- /dev/null
+++ b/arch/microblaze/lib/mulsi3.S
@@ -0,0 +1,47 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#include <linux/linkage.h>
+
+/*
+ * Multiply operation for 32 bit integers.
+ *	Input :	Operand1 in Reg r5
+ *		Operand2 in Reg r6
+ *	Output: Result [op1 * op2] in Reg r3
+ */
+	.text
+	.globl	__mulsi3
+	.type __mulsi3,  @function
+	.ent __mulsi3
+
+__mulsi3:
+	.frame	r1, 0, r15
+	add	r3, r0, r0
+	beqi	r5, result_is_zero /* multiply by zero */
+	beqi	r6, result_is_zero /* multiply by zero */
+	bgeid	r5, r5_pos
+	xor	r4, r5, r6 /* get the sign of the result */
+	rsubi	r5, r5, 0 /* make r5 positive */
+r5_pos:
+	bgei	r6, r6_pos
+	rsubi	r6, r6, 0 /* make r6 positive */
+r6_pos:
+	bri	l1
+l2:
+	add	r5, r5, r5
+l1:
+	srl	r6, r6
+	addc	r7, r0, r0
+	beqi	r7, l2
+	bneid	r6, l2
+	add	r3, r3, r5
+	blti	r4, negateresult
+	rtsd	r15, 8
+	nop
+negateresult:
+	rtsd	r15, 8
+	rsub	r3, r3, r0
+result_is_zero:
+	rtsd	r15, 8
+	addi	r3, r0, 0
+
+.size __mulsi3,  . - __mulsi3
+.end __mulsi3