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@xxxxxxxxxx>
> ---
> 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;
> }
>
--
Ben Hutchings
Nothing is ever a complete failure;
it can always serve as a bad example.
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