[PATCH 5.10 1/1] Reinstate some of "swiotlb: rework "fix info leak with DMA_FROM_DEVICE""

* [PATCH 5.10 1/1] Reinstate some of "swiotlb: rework "fix info leak with DMA_FROM_DEVICE""
@ 2022-05-23 11:40 Ovidiu Panait
  2022-05-23 15:20 ` Greg KH
  0 siblings, 1 reply; 3+ messages in thread
From: Ovidiu Panait @ 2022-05-23 11:40 UTC (permalink / raw)
  To: stable
  Cc: Linus Torvalds, Halil Pasic, Oleksandr Natalenko,
	Christoph Hellwig, Ovidiu Panait

From: Linus Torvalds <torvalds@linux-foundation.org>

commit 901c7280ca0d5e2b4a8929fbe0bfb007ac2a6544 upstream.

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>
[OP: backport to 5.10: adjusted context]
Signed-off-by: Ovidiu Panait <ovidiu.panait@windriver.com>
---
This is part of CVE-2022-0854 patchset:
[1] ddbd89deb7d3 ("swiotlb: fix info leak with DMA_FROM_DEVICE")
[2] 901c7280ca0d ("Reinstate some of "swiotlb: rework "fix info leak with DMA_FROM_DEVICE""")

[1] is already present in 5.10-stable.
[2] is present in 5.17/5.16/5.15, but not in 5.10 and 5.4 branches;

 Documentation/core-api/dma-attributes.rst |  8 --------
 include/linux/dma-mapping.h               |  8 --------
 kernel/dma/swiotlb.c                      | 12 ++++++++----
 3 files changed, 8 insertions(+), 20 deletions(-)

diff --git a/Documentation/core-api/dma-attributes.rst b/Documentation/core-api/dma-attributes.rst
index 17706dc91ec9..1887d92e8e92 100644
--- a/Documentation/core-api/dma-attributes.rst
+++ b/Documentation/core-api/dma-attributes.rst
@@ -130,11 +130,3 @@ 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_OVERWRITE
-------------------
-
-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.
diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index a9361178c5db..a7d70cdee25e 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -61,14 +61,6 @@
  */
 #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.  It is specific to a
diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index 62b1e5fa8673..0882ebf9fcd3 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -597,10 +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) &&
-	    (!(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;
 }
 
-- 
2.36.1


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