[PATCH-for-7.2 1/2] hw/sd/sdhci: Do not set Buf Wr Ena before writing block (CVE-2022-3872)

[Philippe Mathieu-Daudé]

When sdhci_write_block_to_card() is called to transfer data from
the FIFO to the SD bus, the data is already present in the buffer
and we have to consume it directly.

See the description of the 'Buffer Write Enable' bit from the
'Present State' register (prnsts::SDHC_SPACE_AVAILABLE) in Table
2.14 from the SDHCI spec v2:

  Buffer Write Enable

  This status is used for non-DMA write transfers.

  The Host Controller can implement multiple buffers to transfer
  data efficiently. This read only flag indicates if space is
  available for write data. If this bit is 1, data can be written
  to the buffer. A change of this bit from 1 to 0 occurs when all
  the block data is written to the buffer. A change of this bit
  from 0 to 1 occurs when top of block data can be written to the
  buffer and generates the Buffer Write Ready interrupt.

In our case, we do not want to overwrite the buffer, so we want
this bit to be 0, then set it to 1 once the data is written onto
the bus.

This is probably a copy/paste error from commit d7dfca0807
("hw/sdhci: introduce standard SD host controller").

Reproducer:
https://lore.kernel.org/qemu-devel/CAA8xKjXrmS0fkr28AKvNNpyAtM0y0B+5FichpsrhD+mUgnuyKg@mail.gmail.com/

Fixes: CVE-2022-3872
Reported-by: RivenDell <XRivenDell@outlook.com>
Reported-by: Siqi Chen <coc.cyqh@gmail.com>
Reported-by: ningqiang <ningqiang1@huawei.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
---
 hw/sd/sdhci.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hw/sd/sdhci.c b/hw/sd/sdhci.c
index 306070c872..f230e7475f 100644
--- a/hw/sd/sdhci.c
+++ b/hw/sd/sdhci.c
@@ -954,7 +954,7 @@ static void sdhci_data_transfer(void *opaque)
             sdhci_read_block_from_card(s);
         } else {
             s->prnsts |= SDHC_DOING_WRITE | SDHC_DAT_LINE_ACTIVE |
-                    SDHC_SPACE_AVAILABLE | SDHC_DATA_INHIBIT;
+                                           SDHC_DATA_INHIBIT;
             sdhci_write_block_to_card(s);
         }
     }
-- 
2.38.1