Re: [PATCH] drm/msm/adreno: fix userspace-triggered crash on a2xx-a4xx

[Dmitry Baryshkov]

On Mon, Apr 06, 2026 at 03:24:43PM -0700, Rob Clark wrote:
> On Mon, Apr 6, 2026 at 3:14 PM Dmitry Baryshkov
> <dmitry.baryshkov@xxxxxxxxxxxxxxxx> wrote:
> >
> > Before a5xx Adreno driver will not try fetching UBWC params (because
> > those generations didn't support UBWC anyway), however it's still
> > possible to query UBWC-related params from the userspace, triggering
> > possible NULL pointer dereference. Check for UBWC config in
> > adreno_get_param() and return sane defaults if there is none.
> >
> > Fixes: a452510aad53 ("drm/msm/adreno: Switch to the common UBWC config struct")
> > Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxxxxxxxx>
> > ---
> >  drivers/gpu/drm/msm/adreno/adreno_gpu.c | 15 ++++++++++++---
> >  1 file changed, 12 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/msm/adreno/adreno_gpu.c b/drivers/gpu/drm/msm/adreno/adreno_gpu.c
> > index d5fe6f6f0dec..7dc95c0a17f7 100644
> > --- a/drivers/gpu/drm/msm/adreno/adreno_gpu.c
> > +++ b/drivers/gpu/drm/msm/adreno/adreno_gpu.c
> > @@ -426,16 +426,25 @@ int adreno_get_param(struct msm_gpu *gpu, struct msm_context *ctx,
> >                 *value = vm->mm_range;
> >                 return 0;
> >         case MSM_PARAM_HIGHEST_BANK_BIT:
> > -               *value = adreno_gpu->ubwc_config->highest_bank_bit;
> > +               if (!adreno_gpu->ubwc_config)
> > +                       *value = 13;
> > +               else
> > +                       *value = adreno_gpu->ubwc_config->highest_bank_bit;
> 
> These three params are only used by userspace on a6xx, so tbh it would
> be ok to return -ENOENT for platforms that have no ubwc config.  That
> might be better than returning imaginary values.

I'd say, those are defaults. But I agree, -ENOENT might be better.

> 
> BR,
> -R
> 
> >                 return 0;
> >         case MSM_PARAM_RAYTRACING:
> >                 *value = adreno_gpu->has_ray_tracing;
> >                 return 0;
> >         case MSM_PARAM_UBWC_SWIZZLE:
> > -               *value = adreno_gpu->ubwc_config->ubwc_swizzle;
> > +               if (!adreno_gpu->ubwc_config)
> > +                       *value = 0;
> > +               else
> > +                       *value = adreno_gpu->ubwc_config->ubwc_swizzle;
> >                 return 0;
> >         case MSM_PARAM_MACROTILE_MODE:
> > -               *value = adreno_gpu->ubwc_config->macrotile_mode;
> > +               if (!adreno_gpu->ubwc_config)
> > +                       *value = 0;
> > +               else
> > +                       *value = adreno_gpu->ubwc_config->macrotile_mode;
> >                 return 0;
> >         case MSM_PARAM_UCHE_TRAP_BASE:
> >                 *value = adreno_gpu->uche_trap_base;
> >
> > ---
> > base-commit: 36ece9697e89016181e5ae87510e40fb31d86f2b
> > change-id: 20260407-adreno-fix-ubwc-6a2564710e21
> >
> > Best regards,
> > --
> > With best wishes
> > Dmitry
> >

-- 
With best wishes
Dmitry