[RFC PATCH 2/3] hw/sd/sdhci: Prohibit DMA accesses to devices

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

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

The issue reported by OSS-Fuzz produces the following backtrace:

  ==447470==ERROR: AddressSanitizer: heap-buffer-overflow
  READ of size 1 at 0x61500002a080 thread T0
      #0 0x71766d47 in sdhci_read_dataport hw/sd/sdhci.c:474:18
      #1 0x7175f139 in sdhci_read hw/sd/sdhci.c:1022:19
      #2 0x721b937b in memory_region_read_accessor softmmu/memory.c:440:11
      #3 0x72171e51 in access_with_adjusted_size softmmu/memory.c:554:18
      #4 0x7216f47c in memory_region_dispatch_read1 softmmu/memory.c:1424:16
      #5 0x7216ebb9 in memory_region_dispatch_read softmmu/memory.c:1452:9
      #6 0x7212db5d in flatview_read_continue softmmu/physmem.c:2879:23
      #7 0x7212f958 in flatview_read softmmu/physmem.c:2921:12
      #8 0x7212f418 in address_space_read_full softmmu/physmem.c:2934:18
      #9 0x721305a9 in address_space_rw softmmu/physmem.c:2962:16
      #10 0x7175a392 in dma_memory_rw_relaxed include/sysemu/dma.h:89:12
      #11 0x7175a0ea in dma_memory_rw include/sysemu/dma.h:132:12
      #12 0x71759684 in dma_memory_read include/sysemu/dma.h:152:12
      #13 0x7175518c in sdhci_do_adma hw/sd/sdhci.c:823:27
      #14 0x7174bf69 in sdhci_data_transfer hw/sd/sdhci.c:935:13
      #15 0x7176aaa7 in sdhci_send_command hw/sd/sdhci.c:376:9
      #16 0x717629ee in sdhci_write hw/sd/sdhci.c:1212:9
      #17 0x72172513 in memory_region_write_accessor softmmu/memory.c:492:5
      #18 0x72171e51 in access_with_adjusted_size softmmu/memory.c:554:18
      #19 0x72170766 in memory_region_dispatch_write softmmu/memory.c:1504:16
      #20 0x721419ee in flatview_write_continue softmmu/physmem.c:2812:23
      #21 0x721301eb in flatview_write softmmu/physmem.c:2854:12
      #22 0x7212fca8 in address_space_write softmmu/physmem.c:2950:18
      #23 0x721d9a53 in qtest_process_command softmmu/qtest.c:727:9

A DMA descriptor is previously filled in RAM. An I/O access to the
device (frames #22 to #16) start the DMA engine (frame #13). The
engine fetch the descriptor and execute the request, which itself
accesses the SDHCI I/O registers (frame #1 and #0), triggering a
re-entrancy issue.

Fix by prohibit transactions from the DMA to devices. The DMA engine
is thus restricted to memories.

Reported-by: OSS-Fuzz (Issue 36391)
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/451
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
---
 hw/sd/sdhci.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/hw/sd/sdhci.c b/hw/sd/sdhci.c
index fe2f21f0c37..0e5e988927e 100644
--- a/hw/sd/sdhci.c
+++ b/hw/sd/sdhci.c
@@ -741,6 +741,7 @@ static void sdhci_do_adma(SDHCIState *s)
 {
     unsigned int begin, length;
     const uint16_t block_size = s->blksize & BLOCK_SIZE_MASK;
+    const MemTxAttrs attrs = { .memory = true };
     ADMADescr dscr = {};
     MemTxResult res;
     int i;
@@ -794,7 +795,7 @@ static void sdhci_do_adma(SDHCIState *s)
                     res = dma_memory_write(s->dma_as, dscr.addr,
                                            &s->fifo_buffer[begin],
                                            s->data_count - begin,
-                                           MEMTXATTRS_UNSPECIFIED);
+                                           attrs);
                     if (res != MEMTX_OK) {
                         break;
                     }
@@ -823,7 +824,7 @@ static void sdhci_do_adma(SDHCIState *s)
                     res = dma_memory_read(s->dma_as, dscr.addr,
                                           &s->fifo_buffer[begin],
                                           s->data_count - begin,
-                                          MEMTXATTRS_UNSPECIFIED);
+                                          attrs);
                     if (res != MEMTX_OK) {
                         break;
                     }
-- 
2.33.1