hw/dma/xlnx_dpdma: Read descriptor into buffer, not into pointer-to-buffer

[PATCH] hw/dma/xlnx_dpdma: Read descriptor into buffer, not into pointer-to-buffer

Posted by Peter Maydell 5 months, 3 weeks ago

In fdf029762f501 we factored out the handling of reading and writing
DMA descriptors from guest memory.  Unfortunately we accidentally
made the descriptor-read read the descriptor into the address of the
buffer rather than into the buffer, because we didn't notice we
needed to update the arguments to the dma_memory_read() call. Before
the refactoring, "&desc" is the address of a local struct DPDMADescriptor
variable in xlnx_dpdma_start_operation(), which is the correct target
for the guest-memory-read. But after the refactoring 'desc' is the
"DPDMADescriptor *desc" argument to the new function, and so it is
already an address.

This bug is an overrun of a stack variable, since a pointer is at
most 8 bytes long and we try to read 64 bytes, as well as being
incorrect behaviour.

Pass 'desc' rather than '&desc' as the dma_memory_read() argument
to fix this.

(The same bug is not present in xlnx_dpdma_write_descriptor(),
because there we are writing the descriptor from a local struct
variable "DPDMADescriptor tmp_desc" and so passing &tmp_desc to
dma_memory_write() is correct.)

Spotted by Coverity: CID 1546649

Fixes: fdf029762f50101 ("xlnx_dpdma: fix descriptor endianness bug")
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
 hw/dma/xlnx_dpdma.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hw/dma/xlnx_dpdma.c b/hw/dma/xlnx_dpdma.c
index dde4aeca401..a685bd28bb8 100644
--- a/hw/dma/xlnx_dpdma.c
+++ b/hw/dma/xlnx_dpdma.c
@@ -619,7 +619,7 @@ static MemTxResult xlnx_dpdma_read_descriptor(XlnxDPDMAState *s,
                                               DPDMADescriptor *desc)
 {
     MemTxResult res = dma_memory_read(&address_space_memory, desc_addr,
-                                      &desc, sizeof(DPDMADescriptor),
+                                      desc, sizeof(DPDMADescriptor),
                                       MEMTXATTRS_UNSPECIFIED);
     if (res) {
         return res;
-- 
2.34.1

Re: [PATCH] hw/dma/xlnx_dpdma: Read descriptor into buffer, not into pointer-to-buffer

Posted by Philippe Mathieu-Daudé 5 months, 3 weeks ago

On 31/5/24 14:46, Peter Maydell wrote:
> In fdf029762f501 we factored out the handling of reading and writing
> DMA descriptors from guest memory.  Unfortunately we accidentally
> made the descriptor-read read the descriptor into the address of the
> buffer rather than into the buffer, because we didn't notice we
> needed to update the arguments to the dma_memory_read() call. Before
> the refactoring, "&desc" is the address of a local struct DPDMADescriptor
> variable in xlnx_dpdma_start_operation(), which is the correct target
> for the guest-memory-read. But after the refactoring 'desc' is the
> "DPDMADescriptor *desc" argument to the new function, and so it is
> already an address.
> 
> This bug is an overrun of a stack variable, since a pointer is at
> most 8 bytes long and we try to read 64 bytes, as well as being
> incorrect behaviour.
> 
> Pass 'desc' rather than '&desc' as the dma_memory_read() argument
> to fix this.
> 
> (The same bug is not present in xlnx_dpdma_write_descriptor(),
> because there we are writing the descriptor from a local struct
> variable "DPDMADescriptor tmp_desc" and so passing &tmp_desc to
> dma_memory_write() is correct.)
> 
> Spotted by Coverity: CID 1546649
> 
> Fixes: fdf029762f50101 ("xlnx_dpdma: fix descriptor endianness bug")
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
>   hw/dma/xlnx_dpdma.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)

Thanks, patch queued via hw-misc (except if you rather your arm tree).

Re: [PATCH] hw/dma/xlnx_dpdma: Read descriptor into buffer, not into pointer-to-buffer

Posted by Edgar E. Iglesias 5 months, 3 weeks ago

On Fri, May 31, 2024 at 2:46 PM Peter Maydell <peter.maydell@linaro.org>
wrote:

> In fdf029762f501 we factored out the handling of reading and writing
> DMA descriptors from guest memory.  Unfortunately we accidentally
> made the descriptor-read read the descriptor into the address of the
> buffer rather than into the buffer, because we didn't notice we
> needed to update the arguments to the dma_memory_read() call. Before
> the refactoring, "&desc" is the address of a local struct DPDMADescriptor
> variable in xlnx_dpdma_start_operation(), which is the correct target
> for the guest-memory-read. But after the refactoring 'desc' is the
> "DPDMADescriptor *desc" argument to the new function, and so it is
> already an address.
>
> This bug is an overrun of a stack variable, since a pointer is at
> most 8 bytes long and we try to read 64 bytes, as well as being
> incorrect behaviour.
>
> Pass 'desc' rather than '&desc' as the dma_memory_read() argument
> to fix this.
>
> (The same bug is not present in xlnx_dpdma_write_descriptor(),
> because there we are writing the descriptor from a local struct
> variable "DPDMADescriptor tmp_desc" and so passing &tmp_desc to
> dma_memory_write() is correct.)
>
> Spotted by Coverity: CID 1546649
>
>
+ CC Fred.

Reviewed-by: Edgar E. Iglesias <edgar.iglesias@amd.com>




> Fixes: fdf029762f50101 ("xlnx_dpdma: fix descriptor endianness bug")
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
>  hw/dma/xlnx_dpdma.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/hw/dma/xlnx_dpdma.c b/hw/dma/xlnx_dpdma.c
> index dde4aeca401..a685bd28bb8 100644
> --- a/hw/dma/xlnx_dpdma.c
> +++ b/hw/dma/xlnx_dpdma.c
> @@ -619,7 +619,7 @@ static MemTxResult
> xlnx_dpdma_read_descriptor(XlnxDPDMAState *s,
>                                                DPDMADescriptor *desc)
>  {
>      MemTxResult res = dma_memory_read(&address_space_memory, desc_addr,
> -                                      &desc, sizeof(DPDMADescriptor),
> +                                      desc, sizeof(DPDMADescriptor),
>                                        MEMTXATTRS_UNSPECIFIED);
>      if (res) {
>          return res;
> --
> 2.34.1
>
>

Re: [PATCH] hw/dma/xlnx_dpdma: Read descriptor into buffer, not into pointer-to-buffer

Posted by Philippe Mathieu-Daudé 5 months, 3 weeks ago

On 31/5/24 14:46, Peter Maydell wrote:
> In fdf029762f501 we factored out the handling of reading and writing
> DMA descriptors from guest memory.  Unfortunately we accidentally
> made the descriptor-read read the descriptor into the address of the
> buffer rather than into the buffer, because we didn't notice we
> needed to update the arguments to the dma_memory_read() call. Before
> the refactoring, "&desc" is the address of a local struct DPDMADescriptor
> variable in xlnx_dpdma_start_operation(), which is the correct target
> for the guest-memory-read. But after the refactoring 'desc' is the
> "DPDMADescriptor *desc" argument to the new function, and so it is
> already an address.
> 
> This bug is an overrun of a stack variable, since a pointer is at
> most 8 bytes long and we try to read 64 bytes, as well as being
> incorrect behaviour.
> 
> Pass 'desc' rather than '&desc' as the dma_memory_read() argument
> to fix this.
> 
> (The same bug is not present in xlnx_dpdma_write_descriptor(),
> because there we are writing the descriptor from a local struct
> variable "DPDMADescriptor tmp_desc" and so passing &tmp_desc to
> dma_memory_write() is correct.)
> 
> Spotted by Coverity: CID 1546649
> 
> Fixes: fdf029762f50101 ("xlnx_dpdma: fix descriptor endianness bug")
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
>   hw/dma/xlnx_dpdma.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>