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SubjectRe: No check of the size passed to unmap_single in swiotlb
On Mon, Nov 20, 2017 at 08:17:14AM +0000, Eric Yang wrote:
> Hi all,

Hi!
>
> During debug a device only support 32bits DMA(Qualcomm Atheros AP) in our LS1043A 64bits ARM SOC, we found that the invoke of dma_unmap_single --> swiotlb_tbl_unmap_single will unmap the passed "size" anyway even when the "size" is incorrect.
>
> If the size is larger than it should, the extra entries in io_tlb_orig_addr array will be refilled by INVALID_PHYS_ADDR, and it will cause the bounce buffer copy not happen when the one who really used the mis-freed entries doing DMA data transfers, and this will cause further unknow behaviors.
>
> Here we just fix it temporarily by adding a judge of the "size" in the swiotlb_tbl_unmap_single, if it is larger than it deserves, just unmap the right size only. Like the code:

Did the DMA debug API (CONFIG_DMA_API_DEBUG) help in figuring this issue as well?

>
> [yangyu@titan dash-lts]$ git diff ./lib/swiotlb.c
> diff --git a/lib/swiotlb.c b/lib/swiotlb.c
> index ad1d2962d129..58c97ede9d78 100644
> --- a/lib/swiotlb.c
> +++ b/lib/swiotlb.c
> @@ -591,7 +591,10 @@ void swiotlb_tbl_unmap_single(struct device *hwdev, phys_addr_t tlb_addr,
> */
> for (i = index + nslots - 1; i >= index; i--) {
> io_tlb_list[i] = ++count;
> - io_tlb_orig_addr[i] = INVALID_PHYS_ADDR;
> + if(io_tlb_orig_addr[i] != orig_addr)
> + printk("======size wrong, ally down ally down!===\n");
> + else
> + io_tlb_orig_addr[i] = INVALID_PHYS_ADDR;
> }
> /*
> * Step 2: merge the returned slots with the preceding slots,
>
> Although pass a right size of DMA buffer is the responsibility of the drivers, but Is it useful to add some size check code to prevent real damage happen?
>
> Regards,
> Eric

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