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Reinstate some of "swiotlb: rework "fix info leak with DMA_FROM_DEVICE""

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[ Upstream commit 901c7280ca0d5e2b4a8929fbe0bfb007ac2a6544 ]

Halil Pasic points out [1] that the full revert of that commit (revert
in bddac7c1e02b), and that a partial revert that only reverts the
problematic case, but still keeps some of the cleanups is probably
better.  

And that partial revert [2] had already been verified by Oleksandr
Natalenko to also fix the issue, I had just missed that in the long
discussion.

So let's reinstate the cleanups from commit aa6f8dcbab47 ("swiotlb:
rework "fix info leak with DMA_FROM_DEVICE""), and effectively only
revert the part that caused problems.

Link: https://lore.kernel.org/all/20220328013731.017ae3e3.pasic@linux.ibm.com/ [1]
Link: https://lore.kernel.org/all/20220324055732.GB12078@lst.de/ [2]
Link: https://lore.kernel.org/all/4386660.LvFx2qVVIh@natalenko.name/ [3]
Suggested-by: Halil Pasic <pasic@linux.ibm.com>
Tested-by: Oleksandr Natalenko <oleksandr@natalenko.name>
Cc: Christoph Hellwig" <hch@lst.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Linus Torvalds 2022-03-28 11:37:05 -07:00 committed by Greg Kroah-Hartman
parent e2cfa7b093
commit f3f2247ac3
1 changed files with 8 additions and 3 deletions
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11
kernel/dma/swiotlb.c
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@ -597,9 +597,14 @@ phys_addr_t swiotlb_tbl_map_single(struct device *dev, phys_addr_t orig_addr,
io_tlb_orig_addr[index + i] = slot_addr(orig_addr, i);
tlb_addr = slot_addr(io_tlb_start, index) + offset;
if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC) &&
(dir == DMA_TO_DEVICE || dir == DMA_BIDIRECTIONAL))
swiotlb_bounce(orig_addr, tlb_addr, mapping_size, DMA_TO_DEVICE);
/*
* When dir == DMA_FROM_DEVICE we could omit the copy from the orig
* to the tlb buffer, if we knew for sure the device will
* overwirte the entire current content. But we don't. Thus
* unconditional bounce may prevent leaking swiotlb content (i.e.
* kernel memory) to user-space.
*/
swiotlb_bounce(orig_addr, tlb_addr, mapping_size, DMA_TO_DEVICE);
return tlb_addr;
}