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

Documentation/DMA-attributes.txt | 10 ---------- include/linux/dma-mapping.h | 8 -------- kernel/dma/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 da90f20e11c1..4d450672b7d6 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/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c index f17b771856d1..913cb71198af 100644 --- a/kernel/dma/swiotlb.c +++ b/kernel/dma/swiotlb.c @@ -571,11 +571,14 @@ 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, 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; }