Re: [PATCH] drm/vc4: Fix NULL pointer dereference in vc4_save_hang_state()

[Eric Anholt <eric@anholt.net>]

[-- Attachment #1: Type: text/plain, Size: 1383 bytes --]

Boris Brezillon <boris.brezillon@free-electrons.com> writes:

> When saving BOs in the hang state we skip one entry of the
> kernel_state->bo[] array, thus leaving it to NULL. This leads to a NULL
> pointer dereference when, later in this function, we iterate over all
> BOs to check their ->madv state.
>
> Fixes: ca26d28bbaa3 ("drm/vc4: improve throughput by pipelining binning and rendering jobs")
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
> ---
>  drivers/gpu/drm/vc4/vc4_gem.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/vc4/vc4_gem.c b/drivers/gpu/drm/vc4/vc4_gem.c
> index 6c32c89a83a9..19ac7fe0e5db 100644
> --- a/drivers/gpu/drm/vc4/vc4_gem.c
> +++ b/drivers/gpu/drm/vc4/vc4_gem.c
> @@ -208,7 +208,7 @@ vc4_save_hang_state(struct drm_device *dev)
>  			kernel_state->bo[j + prev_idx] = &bo->base.base;
>  			j++;
>  		}
> -		prev_idx = j + 1;
> +		prev_idx = j;

Could we replace the whole "[j + prev_idx]" with a "[k++]" and maybe a
WARN_ON_ONCE(k != state->bo_count) at the end?

I really need to figure out if I can come up with a way to make IGT
cases for GPU hangs on vc4, despite the validation.  I found a bug in
GPU reset due to BCL hangs when doing vc5, but I don't have a testcase.
Maybe some submit flags that overwrite the BCL or RCL to do an infinite
loop?

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 832 bytes --]