[PATCH] drm/i915/guc: prevent a possible int overflow in wq offsets

[Rodrigo Vivi]

On Thu, Jul 25, 2024 at 08:59:25AM -0700, Nikita Zhandarovich wrote:
> It may be possible for the sum of the values derived from
> i915_ggtt_offset() and __get_parent_scratch_offset()/
> i915_ggtt_offset() to go over the u32 limit before being assigned
> to wq offsets of u64 type.
> 
> Mitigate these issues by expanding one of the right operands
> to u64 to avoid any overflow issues just in case.
> 
> Found by Linux Verification Center (linuxtesting.org) with static
> analysis tool SVACE.
> 
> Fixes: 2584b3549f4c ("drm/i915/guc: Update to GuC version 70.1.1")

this is not the correct fixes tag. The code is like this since

Fixes: c2aa552ff09d ("drm/i915/guc: Add multi-lrc context registration")
Cc: Matthew Brost <matthew.brost at intel.com>
Cc: John Harrison <John.C.Harrison at Intel.com>

Also, this is theoretical only since I don't believe it is actually
possible like Tvrtko had mentioned already.

But let's give a piece of mind to the static analyzers and get this in.

Reviewed-by: Rodrigo Vivi <rodrigo.vivi at intel.com>

(pushing now with the fixes fixes tag)

> Cc: stable at vger.kernel.org
> Signed-off-by: Nikita Zhandarovich <n.zhandarovich at fintech.ru>
> ---
>  drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> index 9400d0eb682b..908ebfa22933 100644
> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> @@ -2842,9 +2842,9 @@ static void prepare_context_registration_info_v70(struct intel_context *ce,
>  		ce->parallel.guc.wqi_tail = 0;
>  		ce->parallel.guc.wqi_head = 0;
>  
> -		wq_desc_offset = i915_ggtt_offset(ce->state) +
> +		wq_desc_offset = (u64)i915_ggtt_offset(ce->state) +
>  				 __get_parent_scratch_offset(ce);
> -		wq_base_offset = i915_ggtt_offset(ce->state) +
> +		wq_base_offset = (u64)i915_ggtt_offset(ce->state) +
>  				 __get_wq_offset(ce);
>  		info->wq_desc_lo = lower_32_bits(wq_desc_offset);
>  		info->wq_desc_hi = upper_32_bits(wq_desc_offset);