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

[P J P <ppandit@redhat.com>]

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;
-- 
2.26.2