From: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
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@xxxxxxxxxxxxx/ [1]
Link: https://lore.kernel.org/all/20220324055732.GB12078@xxxxxx/ [2]
Link: https://lore.kernel.org/all/4386660.LvFx2qVVIh@xxxxxxxxxxxxxx/ [3]
Suggested-by: Halil Pasic <pasic@xxxxxxxxxxxxx>
Tested-by: Oleksandr Natalenko <oleksandr@xxxxxxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
[OP: backport to 4.14: apply swiotlb_tbl_map_single() changes in lib/swiotlb.c]
Signed-off-by: Ovidiu Panait <ovidiu.panait@xxxxxxxxxxxxx>
---
Documentation/DMA-attributes.txt | 10 ----------
include/linux/dma-mapping.h | 8 --------
lib/swiotlb.c | 13 ++++++++-----
3 files changed, 8 insertions(+), 23 deletions(-)
diff --git a/Documentation/DMA-attributes.txt b/Documentation/DMA-attributes.txt
index 7193505a98ca..8f8d97f65d73 100644
--- a/Documentation/DMA-attributes.txt
+++ b/Documentation/DMA-attributes.txt
@@ -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).
diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index 93fa253f2a37..9aee5f345e29 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -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
diff --git a/lib/swiotlb.c b/lib/swiotlb.c
index 5796aa1e5cbd..bdc2b89870e3 100644
--- a/lib/swiotlb.c
+++ b/lib/swiotlb.c
@@ -600,11 +600,14 @@ phys_addr_t swiotlb_tbl_map_single(struct device *hwdev,
*/
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, 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, size, DMA_TO_DEVICE);
return tlb_addr;
}
EXPORT_SYMBOL_GPL(swiotlb_tbl_map_single);
--
2.36.1
