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, 121 insertions, 0 deletions

diff --git a/arch/m68k/lib/memmove.c b/arch/m68k/lib/memmove.c
new file mode 100644
index 000000000..e33f00b02
--- /dev/null
+++ b/arch/m68k/lib/memmove.c
@@ -0,0 +1,121 @@
+/*
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file COPYING in the main directory of this archive
+ * for more details.
+ */
+
+#include <linux/module.h>
+#include <linux/string.h>
+
+void *memmove(void *dest, const void *src, size_t n)
+{
+	void *xdest = dest;
+	size_t temp;
+
+	if (!n)
+		return xdest;
+
+	if (dest < src) {
+		if ((long)dest & 1) {
+			char *cdest = dest;
+			const char *csrc = src;
+			*cdest++ = *csrc++;
+			dest = cdest;
+			src = csrc;
+			n--;
+		}
+#if defined(CONFIG_M68000)
+		if ((long)src & 1) {
+			char *cdest = dest;
+			const char *csrc = src;
+			for (; n; n--)
+				*cdest++ = *csrc++;
+			return xdest;
+		}
+#endif
+		if (n > 2 && (long)dest & 2) {
+			short *sdest = dest;
+			const short *ssrc = src;
+			*sdest++ = *ssrc++;
+			dest = sdest;
+			src = ssrc;
+			n -= 2;
+		}
+		temp = n >> 2;
+		if (temp) {
+			long *ldest = dest;
+			const long *lsrc = src;
+			temp--;
+			do
+				*ldest++ = *lsrc++;
+			while (temp--);
+			dest = ldest;
+			src = lsrc;
+		}
+		if (n & 2) {
+			short *sdest = dest;
+			const short *ssrc = src;
+			*sdest++ = *ssrc++;
+			dest = sdest;
+			src = ssrc;
+		}
+		if (n & 1) {
+			char *cdest = dest;
+			const char *csrc = src;
+			*cdest = *csrc;
+		}
+	} else {
+		dest = (char *)dest + n;
+		src = (const char *)src + n;
+		if ((long)dest & 1) {
+			char *cdest = dest;
+			const char *csrc = src;
+			*--cdest = *--csrc;
+			dest = cdest;
+			src = csrc;
+			n--;
+		}
+#if defined(CONFIG_M68000)
+		if ((long)src & 1) {
+			char *cdest = dest;
+			const char *csrc = src;
+			for (; n; n--)
+				*--cdest = *--csrc;
+			return xdest;
+		}
+#endif
+		if (n > 2 && (long)dest & 2) {
+			short *sdest = dest;
+			const short *ssrc = src;
+			*--sdest = *--ssrc;
+			dest = sdest;
+			src = ssrc;
+			n -= 2;
+		}
+		temp = n >> 2;
+		if (temp) {
+			long *ldest = dest;
+			const long *lsrc = src;
+			temp--;
+			do
+				*--ldest = *--lsrc;
+			while (temp--);
+			dest = ldest;
+			src = lsrc;
+		}
+		if (n & 2) {
+			short *sdest = dest;
+			const short *ssrc = src;
+			*--sdest = *--ssrc;
+			dest = sdest;
+			src = ssrc;
+		}
+		if (n & 1) {
+			char *cdest = dest;
+			const char *csrc = src;
+			*--cdest = *--csrc;
+		}
+	}
+	return xdest;
+}
+EXPORT_SYMBOL(memmove);