Re: [PATCH v1] sd: sdhci: assert data_count is within fifo_buffer

[Philippe Mathieu-Daudé]

On 9/3/20 9:08 AM, P J P wrote:
> From: Prasad J Pandit <pjp@fedoraproject.org>
> 
> While doing multi block SDMA, transfer block size may exceed
> the 's->fifo_buffer[s->buf_maxsz]' size. It may leave the
> current element pointer 's->data_count' pointing out of bounds.
> Leading the subsequent DMA r/w operation to OOB access issue.
> Assert that 's->data_count' is within fifo_buffer.
> 
>  -> 
> https://ruhr-uni-bochum.sciebo.de/s/NNWP2GfwzYKeKwE?path=%2Fsdhci_oob_write1
>  ==1459837==ERROR: AddressSanitizer: heap-buffer-overflow
>  WRITE of size 54722048 at 0x61500001e280 thread T3
>  #0  __interceptor_memcpy (/lib64/libasan.so.6+0x3a71d)
>  #1  flatview_read_continue ../exec.c:3245
>  #2  flatview_read ../exec.c:3278
>  #3  address_space_read_full ../exec.c:3291
>  #4  address_space_rw ../exec.c:3319
>  #5  dma_memory_rw_relaxed ../include/sysemu/dma.h:87
>  #6  dma_memory_rw ../include/sysemu/dma.h:110
>  #7  dma_memory_read ../include/sysemu/dma.h:116
>  #8  sdhci_sdma_transfer_multi_blocks ../hw/sd/sdhci.c:629
>  #9  sdhci_write ../hw/sd/sdhci.c:1097
>  #10 memory_region_write_accessor ../softmmu/memory.c:483
>  ...
> 
> Reported-by: Ruhr-University <bugs-syssec@rub.de>
> Suggested-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
> Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
> ---
>  hw/sd/sdhci.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> Update v1: use assert(3) calls
>   -> https://lists.nongnu.org/archive/html/qemu-devel/2020-09/msg00966.html
> 
> diff --git a/hw/sd/sdhci.c b/hw/sd/sdhci.c
> index 1785d7e1f7..023acbed41 100644
> --- a/hw/sd/sdhci.c
> +++ b/hw/sd/sdhci.c
> @@ -604,6 +604,7 @@ static void sdhci_sdma_transfer_multi_blocks(SDHCIState 
> *s)
>                      s->blkcnt--;
>                  }
>              }
> +            assert(s->data_count <= s->buf_maxsz && s->data_count > begin);
>              dma_memory_write(s->dma_as, s->sdmasysad,
>                               &s->fifo_buffer[begin], s->data_count - begin);
>              s->sdmasysad += s->data_count - begin;
> @@ -626,6 +627,7 @@ static void sdhci_sdma_transfer_multi_blocks(SDHCIState 
> *s)
>                  s->data_count = block_size;
>                  boundary_count -= block_size - begin;
>              }
> +            assert(s->data_count <= s->buf_maxsz && s->data_count > begin);
>              dma_memory_read(s->dma_as, s->sdmasysad,
>                              &s->fifo_buffer[begin], s->data_count - begin);
>              s->sdmasysad += s->data_count - begin;
> 

qemu-system-i386: hw/sd/sdhci.c:632: void
sdhci_sdma_transfer_multi_blocks(SDHCIState *): Assertion `s->data_count
<= s->buf_maxsz && s->data_count > begin' failed.

Tested-by: Philippe Mathieu-Daudé <f4bug@amsat.org>

If you don't mind I might split the assert in 2 when applying:

-            assert(s->data_count <= s->buf_maxsz && s->data_count > begin);
+            assert(s->data_count <= s->buf_maxsz);
+            assert(s->data_count > begin);

To directly display the problem straight:

qemu-system-i386: hw/sd/sdhci.c:635: void
sdhci_sdma_transfer_multi_blocks(SDHCIState *): Assertion `s->data_count
> begin' failed.

Thanks,

Phil.