RE: No check of the size passed to unmap_single in swiotlb

[Eric Yang]

> -----Original Message-----
> From: Konrad Rzeszutek Wilk [mailto:konrad.wilk@xxxxxxxxxx]
> Sent: Tuesday, November 21, 2017 12:27 AM
> To: Eric Yang <yu.yang_3@xxxxxxx>; iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx; Greg Kroah-Hartman
> <gregkh@xxxxxxxxxxxxxxxxxxx>; Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>;
> Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>; David Miller
> <davem@xxxxxxxxxxxxx>; Ingo Molnar <mingo@xxxxxxxxxx>; Geert
> Uytterhoeven <geert+renesas@xxxxxxxxx>; Al Viro <viro@xxxxxxxxxxxxxxxxxx>;
> Kees Cook <keescook@xxxxxxxxxxxx>; Daniel Borkmann
> <daniel@xxxxxxxxxxxxx>
> 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!

Hi  Konrad,
> >
> > 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?
> 

I have just enabled this config and move off the kernel fix and test, there seems the debug API 
has no output for this size incorrect issue. For I only enable the config and no other operations 
and my kernel is 4.9, do I missed something?

I confirm that the debug API is working, for there are other drivers triggered its warning output 
like:
 
caam_jr 1710000.jr: DMA-API: device driver tries to free DMA memory it has not allocated 
[device address=0x6800458400000000]

> >
> > [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