linux-stable/kernel/dma
Halil Pasic ddbd89deb7 swiotlb: fix info leak with DMA_FROM_DEVICE
The problem I'm addressing was discovered by the LTP test covering
cve-2018-1000204.

A short description of what happens follows:
1) The test case issues a command code 00 (TEST UNIT READY) via the SG_IO
   interface with: dxfer_len == 524288, dxdfer_dir == SG_DXFER_FROM_DEV
   and a corresponding dxferp. The peculiar thing about this is that TUR
   is not reading from the device.
2) In sg_start_req() the invocation of blk_rq_map_user() effectively
   bounces the user-space buffer. As if the device was to transfer into
   it. Since commit a45b599ad8 ("scsi: sg: allocate with __GFP_ZERO in
   sg_build_indirect()") we make sure this first bounce buffer is
   allocated with GFP_ZERO.
3) For the rest of the story we keep ignoring that we have a TUR, so the
   device won't touch the buffer we prepare as if the we had a
   DMA_FROM_DEVICE type of situation. My setup uses a virtio-scsi device
   and the  buffer allocated by SG is mapped by the function
   virtqueue_add_split() which uses DMA_FROM_DEVICE for the "in" sgs (here
   scatter-gather and not scsi generics). This mapping involves bouncing
   via the swiotlb (we need swiotlb to do virtio in protected guest like
   s390 Secure Execution, or AMD SEV).
4) When the SCSI TUR is done, we first copy back the content of the second
   (that is swiotlb) bounce buffer (which most likely contains some
   previous IO data), to the first bounce buffer, which contains all
   zeros.  Then we copy back the content of the first bounce buffer to
   the user-space buffer.
5) The test case detects that the buffer, which it zero-initialized,
  ain't all zeros and fails.

One can argue that this is an swiotlb problem, because without swiotlb
we leak all zeros, and the swiotlb should be transparent in a sense that
it does not affect the outcome (if all other participants are well
behaved).

Copying the content of the original buffer into the swiotlb buffer is
the only way I can think of to make swiotlb transparent in such
scenarios. So let's do just that if in doubt, but allow the driver
to tell us that the whole mapped buffer is going to be overwritten,
in which case we can preserve the old behavior and avoid the performance
impact of the extra bounce.

Signed-off-by: Halil Pasic <pasic@linux.ibm.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
2022-02-14 10:22:28 +01:00
..
coherent.c dma-mapping: use 'bitmap_zalloc()' when applicable 2021-10-27 08:20:09 +02:00
contiguous.c dma-contiguous: fix a typo error in a comment 2020-11-27 10:33:42 +01:00
debug.c dma-debug: teach add_dma_entry() about DMA_ATTR_SKIP_CPU_SYNC 2021-10-18 12:46:45 +02:00
debug.h dma-debug: teach add_dma_entry() about DMA_ATTR_SKIP_CPU_SYNC 2021-10-18 12:46:45 +02:00
direct.c dma-direct: add a dma_direct_use_pool helper 2021-12-08 16:46:35 +01:00
direct.h swiotlb: Use is_swiotlb_force_bounce for swiotlb data bouncing 2021-07-13 20:04:43 -04:00
dummy.c dma-mapping: return error code from dma_dummy_map_sg() 2021-08-09 17:13:06 +02:00
Kconfig Merge branch 'stable/for-linus-5.15' of git://git.kernel.org/pub/scm/linux/kernel/git/konrad/swiotlb 2021-09-03 10:34:44 -07:00
Makefile dma-mapping updates for 5.11: 2020-12-22 13:19:43 -08:00
map_benchmark.c dma-mapping: benchmark: Add support for multi-pages map/unmap 2021-04-02 16:41:08 +02:00
mapping.c arm64 updates for 5.16 2021-11-01 16:33:53 -07:00
ops_helpers.c dma-mapping: handle vmalloc addresses in dma_common_{mmap,get_sgtable} 2021-07-16 11:30:26 +02:00
pool.c dma/pool: create dma atomic pool only if dma zone has managed pages 2022-01-15 16:30:29 +02:00
remap.c kernel/dma: remove unnecessary unmap_kernel_range 2021-04-30 11:20:40 -07:00
swiotlb.c swiotlb: fix info leak with DMA_FROM_DEVICE 2022-02-14 10:22:28 +01:00