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, 61 insertions, 0 deletions

diff --git a/drivers/md/dm-pcache/segment.c b/drivers/md/dm-pcache/segment.c
new file mode 100644
index 000000000..7e9818701
--- /dev/null
+++ b/drivers/md/dm-pcache/segment.c
@@ -0,0 +1,61 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+#include <linux/dax.h>
+
+#include "pcache_internal.h"
+#include "cache_dev.h"
+#include "segment.h"
+
+int segment_copy_to_bio(struct pcache_segment *segment,
+		u32 data_off, u32 data_len, struct bio *bio, u32 bio_off)
+{
+	struct iov_iter iter;
+	size_t copied;
+	void *src;
+
+	iov_iter_bvec(&iter, ITER_DEST, &bio->bi_io_vec[bio->bi_iter.bi_idx],
+			bio_segments(bio), bio->bi_iter.bi_size);
+	iter.iov_offset = bio->bi_iter.bi_bvec_done;
+	if (bio_off)
+		iov_iter_advance(&iter, bio_off);
+
+	src = segment->data + data_off;
+	copied = _copy_mc_to_iter(src, data_len, &iter);
+	if (copied != data_len)
+		return -EIO;
+
+	return 0;
+}
+
+int segment_copy_from_bio(struct pcache_segment *segment,
+		u32 data_off, u32 data_len, struct bio *bio, u32 bio_off)
+{
+	struct iov_iter iter;
+	size_t copied;
+	void *dst;
+
+	iov_iter_bvec(&iter, ITER_SOURCE, &bio->bi_io_vec[bio->bi_iter.bi_idx],
+			bio_segments(bio), bio->bi_iter.bi_size);
+	iter.iov_offset = bio->bi_iter.bi_bvec_done;
+	if (bio_off)
+		iov_iter_advance(&iter, bio_off);
+
+	dst = segment->data + data_off;
+	copied = _copy_from_iter_flushcache(dst, data_len, &iter);
+	if (copied != data_len)
+		return -EIO;
+	pmem_wmb();
+
+	return 0;
+}
+
+void pcache_segment_init(struct pcache_cache_dev *cache_dev, struct pcache_segment *segment,
+		      struct pcache_segment_init_options *options)
+{
+	segment->seg_info = options->seg_info;
+	segment_info_set_type(segment->seg_info, options->type);
+
+	segment->cache_dev = cache_dev;
+	segment->seg_id = options->seg_id;
+	segment->data_size = PCACHE_SEG_SIZE - options->data_off;
+	segment->data = CACHE_DEV_SEGMENT(cache_dev, options->seg_id) + options->data_off;
+}