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, 44 insertions, 0 deletions

diff --git a/block/partitions/mac.h b/block/partitions/mac.h
new file mode 100644
index 000000000..0e41c9da7
--- /dev/null
+++ b/block/partitions/mac.h
@@ -0,0 +1,44 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ *  fs/partitions/mac.h
+ */
+
+#define MAC_PARTITION_MAGIC	0x504d
+
+/* type field value for A/UX or other Unix partitions */
+#define APPLE_AUX_TYPE	"Apple_UNIX_SVR2"
+
+struct mac_partition {
+	__be16	signature;	/* expected to be MAC_PARTITION_MAGIC */
+	__be16	res1;
+	__be32	map_count;	/* # blocks in partition map */
+	__be32	start_block;	/* absolute starting block # of partition */
+	__be32	block_count;	/* number of blocks in partition */
+	char	name[32];	/* partition name */
+	char	type[32];	/* string type description */
+	__be32	data_start;	/* rel block # of first data block */
+	__be32	data_count;	/* number of data blocks */
+	__be32	status;		/* partition status bits */
+	__be32	boot_start;
+	__be32	boot_size;
+	__be32	boot_load;
+	__be32	boot_load2;
+	__be32	boot_entry;
+	__be32	boot_entry2;
+	__be32	boot_cksum;
+	char	processor[16];	/* identifies ISA of boot */
+	/* there is more stuff after this that we don't need */
+};
+
+#define MAC_STATUS_BOOTABLE	8	/* partition is bootable */
+
+#define MAC_DRIVER_MAGIC	0x4552
+
+/* Driver descriptor structure, in block 0 */
+struct mac_driver_desc {
+	__be16	signature;	/* expected to be MAC_DRIVER_MAGIC */
+	__be16	block_size;
+	__be32	block_count;
+    /* ... more stuff */
+};
+