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 4.14: apply swiotlb_tbl_map_single() changes in lib/swiotlb.c] Signed-off-by: Ovidiu Panait ovidiu.panait@windriver.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org [bwh: Backported to 4.9: adjust context] Signed-off-by: Ben Hutchings ben@decadent.org.uk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- Documentation/DMA-attributes.txt | 10 ---------- include/linux/dma-mapping.h | 7 ------- lib/swiotlb.c | 12 ++++++++---- 3 files changed, 8 insertions(+), 21 deletions(-)
--- a/Documentation/DMA-attributes.txt +++ b/Documentation/DMA-attributes.txt @@ -143,13 +143,3 @@ So, this provides a way for drivers to a where allocation failures are not a problem, and shouldn't bother the logs.
NOTE: At the moment DMA_ATTR_NO_WARN is only implemented on PowerPC. - -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). --- a/include/linux/dma-mapping.h +++ b/include/linux/dma-mapping.h @@ -61,13 +61,6 @@ * allocation failure reports (similarly to __GFP_NOWARN). */ #define DMA_ATTR_NO_WARN (1UL << 8) -/* - * 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. --- a/lib/swiotlb.c +++ b/lib/swiotlb.c @@ -532,10 +532,14 @@ found: */ for (i = 0; i < nslots; i++) io_tlb_orig_addr[index+i] = orig_addr + (i << IO_TLB_SHIFT); - if (!(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);