linux-kernel - Re: No check of the size passed to unmap

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Date:   Mon, 20 Nov 2017 11:26:52 -0500
From:   Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:     Eric Yang <yu.yang_3@....com>, iommu@...ts.linux-foundation.org
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        David Miller <davem@...emloft.net>,
        Ingo Molnar <mingo@...nel.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Al Viro <viro@...iv.linux.org.uk>,
        Kees Cook <keescook@...omium.org>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: Re: 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@...an 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