Re: [PATCH] hw/cxl: Fix out of bound array access

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

Hi Dmitry,

On 13/9/23 12:10, Dmitry Frolov wrote:
> According to cxl_interleave_ways_enc(),
> fw->num_targets is allowed to be up to 16.
> This also corresponds to CXL specs.
> So, the fw->target_hbs[] array is iterated from 0 to 15.
> But it is staticaly declared of length 8.

"statically"

> Thus, out of bound array access may occur.
> 
> Fixes: c28db9e000 ("hw/pci-bridge: Make PCIe and CXL PXB Devices inherit from TYPE_PXB_DEV")
> 
> Signed-off-by: Dmitry Frolov <frolov@swemel.ru>
> ---
>   include/hw/cxl/cxl.h | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/hw/cxl/cxl.h b/include/hw/cxl/cxl.h
> index 56c9e7676e..4944725849 100644
> --- a/include/hw/cxl/cxl.h
> +++ b/include/hw/cxl/cxl.h
> @@ -29,7 +29,7 @@ typedef struct PXBCXLDev PXBCXLDev;
>   typedef struct CXLFixedWindow {
>       uint64_t size;
>       char **targets;
> -    PXBCXLDev *target_hbs[8];
> +    PXBCXLDev *target_hbs[16];
>       uint8_t num_targets;
>       uint8_t enc_int_ways;
>       uint8_t enc_int_gran;

The loop in cxl_fixed_memory_window_config() is indeed unsafe.

OOB can be catched adding:

-- >8 --
diff --git a/hw/cxl/cxl-host.c b/hw/cxl/cxl-host.c
index 034c7805b3..fe9143409b 100644
--- a/hw/cxl/cxl-host.c
+++ b/hw/cxl/cxl-host.c
@@ -33,6 +33,7 @@ static void cxl_fixed_memory_window_config(CXLState 
*cxl_state,
      for (target = object->targets; target; target = target->next) {
          fw->num_targets++;
      }
+    assert(fw->num_targets <= ARRAY_SIZE(fw->target_hbs));

      fw->enc_int_ways = cxl_interleave_ways_enc(fw->num_targets, errp);
      if (*errp) {
---

If Jonathan concurs, please add to your patch.

Thanks,

Phil.