On Thu, 2022-06-30 at 19:33 +0800, Liu Shixin wrote:

After patch ddbd89deb7d3 ("swiotlb: fix info leak with DMA_FROM_DEVICE"), swiotlb_bounce will be called in swiotlb_tbl_map_single unconditionally. This requires that the physical address must be valid, which is not always true on stable-4.19 or earlier version. On stable-4.19, swiotlb_alloc_buffer will call swiotlb_tbl_map_single with orig_addr equal to zero, which cause such a panic:

Unable to handle kernel paging request at virtual address ffffb77a40000000 ... pc : __memcpy+0x100/0x180 lr : swiotlb_bounce+0x74/0x88 ... Call trace: __memcpy+0x100/0x180 swiotlb_tbl_map_single+0x2c8/0x338 swiotlb_alloc+0xb4/0x198 __dma_alloc+0x84/0x1d8 ...

On stable-4.9 and stable-4.14, swiotlb_alloc_coherent wille call map_single with orig_addr equal to zero, which can cause same panic.

Fix this by skipping swiotlb_bounce when orig_addr is zero.

Thanks for fixing this. I tried to test the backports by forcing use of swiotlb, but apparently it still didn't get used.

Ben.

Fixes: ddbd89deb7d3 ("swiotlb: fix info leak with DMA_FROM_DEVICE") Signed-off-by: Liu Shixin liushixin2@huawei.com

---

kernel/dma/swiotlb.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c index 8b1360772fc5..b1e2ce2f9c2d 100644 --- a/kernel/dma/swiotlb.c +++ b/kernel/dma/swiotlb.c @@ -594,7 +594,8 @@ phys_addr_t swiotlb_tbl_map_single(struct device *hwdev, * unconditional bounce may prevent leaking swiotlb content (i.e. * kernel memory) to user-space. */

• swiotlb_bounce(orig_addr, tlb_addr, size, DMA_TO_DEVICE);

• if (orig_addr)

• swiotlb_bounce(orig_addr, tlb_addr, size, DMA_TO_DEVICE);
  

  return tlb_addr;

}