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, 36 insertions, 0 deletions

diff --git a/block/partitions/atari.h b/block/partitions/atari.h
new file mode 100644
index 000000000..678202442
--- /dev/null
+++ b/block/partitions/atari.h
@@ -0,0 +1,36 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ *  fs/partitions/atari.h
+ *  Moved by Russell King from:
+ *
+ * linux/include/linux/atari_rootsec.h
+ * definitions for Atari Rootsector layout
+ * by Andreas Schwab (schwab@ls5.informatik.uni-dortmund.de)
+ *
+ * modified for ICD/Supra partitioning scheme restricted to at most 12
+ * partitions
+ * by Guenther Kelleter (guenther@pool.informatik.rwth-aachen.de)
+ */
+
+#include <linux/compiler.h>
+
+struct partition_info
+{
+  u8 flg;			/* bit 0: active; bit 7: bootable */
+  char id[3];			/* "GEM", "BGM", "XGM", or other */
+  __be32 st;			/* start of partition */
+  __be32 siz;			/* length of partition */
+};
+
+struct rootsector
+{
+  char unused[0x156];		/* room for boot code */
+  struct partition_info icdpart[8];	/* info for ICD-partitions 5..12 */
+  char unused2[0xc];
+  u32 hd_siz;			/* size of disk in blocks */
+  struct partition_info part[4];
+  u32 bsl_st;			/* start of bad sector list */
+  u32 bsl_cnt;			/* length of bad sector list */
+  u16 checksum;			/* checksum for bootable disks */
+} __packed;
+