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

commit 901c7280ca upstream.

Halil Pasic points out [1] that the full revert of that commit (revert
in bddac7c1e0), 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 aa6f8dcbab ("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>
[OP: backport to 5.4: adjusted context]
Signed-off-by: Ovidiu Panait <ovidiu.panait@windriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Linus Torvalds 2022-03-28 11:37:05 -07:00 committed by Greg Kroah-Hartman
parent 060f38b1df
commit b2f140a9f9
3 changed files with 8 additions and 23 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
Documentation/DMA-attributes.txt
View File

@ -156,13 +156,3 @@ accesses to DMA buffers in both privileged "supervisor" and unprivileged
subsystem that the buffer is fully accessible at the elevated privilege
level (and ideally inaccessible or at least read-only at the
lesser-privileged levels).
DMA_ATTR_PRIVILEGED
-------------------
Some advanced peripherals such as remote processors and GPUs perform
accesses to DMA buffers in both privileged "supervisor" and unprivileged
"user" modes. This attribute is used to indicate to the DMA-mapping
subsystem that the buffer is fully accessible at the elevated privilege
level (and ideally inaccessible or at least read-only at the
lesser-privileged levels).

8
include/linux/dma-mapping.h
View File

@ -70,14 +70,6 @@
*/
#define DMA_ATTR_PRIVILEGED (1UL << 9)
/*
* This is a hint to the DMA-mapping subsystem that the device is expected
* to overwrite the entire mapped size, thus the caller does not require any
* of the previous buffer contents to be preserved. This allows
* bounce-buffering implementations to optimise DMA_FROM_DEVICE transfers.
*/
#define DMA_ATTR_OVERWRITE (1UL << 10)
/*
* A dma_addr_t can hold any valid DMA or bus address for the platform.
* It can be given to a device to use as a DMA source or target. A CPU cannot

13
kernel/dma/swiotlb.c
View File

@ -571,11 +571,14 @@ found:
*/
for (i = 0; i < nslots; i++)
io_tlb_orig_addr[index+i] = orig_addr + (i << IO_TLB_SHIFT);
if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC) &&
(!(attrs & DMA_ATTR_OVERWRITE) || 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;
}