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
..
irq	irq: remove handle_domain_{irq,nmi}()	2021-10-26 10:13:31 +01:00
assoc_array.rst
boot-time-mm.rst
bus-virt-phys-mapping.rst	docs: core-api: avoid using ReST :doc:foo markup	2021-06-17 13:24:37 -06:00
cachetlb.rst	mm: Add flush_dcache_folio()	2021-10-18 07:49:36 -04:00
circular-buffers.rst
cpu_hotplug.rst	Documentation: core-api/cpuhotplug: Rewrite the API section	2021-09-11 00:41:21 +02:00
debug-objects.rst
debugging-via-ohci1394.rst
dma-api-howto.rst
dma-api.rst	docs: core-api: avoid using ReST :doc:foo markup	2021-06-17 13:24:37 -06:00
dma-attributes.rst	swiotlb: fix info leak with DMA_FROM_DEVICE	2022-02-14 10:22:28 +01:00
dma-isa-lpc.rst	docs: core-api: avoid using ReST :doc:foo markup	2021-06-17 13:24:37 -06:00
errseq.rst
genalloc.rst
generic-radix-tree.rst
genericirq.rst
gfp_mask-from-fs-io.rst
idr.rst
index.rst	docs: core-api: avoid using ReST :doc:foo markup	2021-06-17 13:24:37 -06:00
kernel-api.rst	Convert xfs/iomap to use folios	2022-01-12 12:51:41 -08:00
kobject.rst	kobject documentation: remove default_attrs information	2022-01-07 11:23:37 +01:00
kref.rst
librs.rst
local_ops.rst
memory-allocation.rst
memory-hotplug.rst	mm/memory_hotplug: remove HIGHMEM leftovers	2021-11-06 13:30:42 -07:00
mm-api.rst	mm/util: Add folio_mapping() and folio_file_mapping()	2021-09-27 09:27:30 -04:00
packing.rst
padata.rst
pin_user_pages.rst	selftests/vm: only some gup_test items are really benchmarks	2020-12-15 12:13:38 -08:00
printk-basics.rst	printk: Move the printk() kerneldoc comment to its new home	2021-07-26 12:36:44 +02:00
printk-formats.rst	vsprintf: Update %pGp documentation about that it prints hex value	2021-11-01 15:55:06 +01:00
protection-keys.rst
rbtree.rst	docs: rbtree.rst: Fix a typo	2021-03-25 11:38:51 -06:00
refcount-vs-atomic.rst
symbol-namespaces.rst	docs/core-api: Consistent code style	2021-05-03 16:52:50 -06:00
this_cpu_ops.rst
timekeeping.rst
tracepoint.rst
unaligned-memory-access.rst
workqueue.rst	workqueue: doc: Call out the non-reentrance conditions	2021-10-25 07:18:40 -10:00
xarray.rst