[PATCH v3] drm/msm/adreno: fix userspace-triggered crash on a2xx-a4xx

[PATCH v3] drm/msm/adreno: fix userspace-triggered crash on a2xx-a4xx

[Dmitry Baryshkov]

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@oss.qualcomm.com>
---
Changes in v3:
- Switched to UERR (Rob)
- Link to v2: https://patch.msgid.link/20260407-adreno-fix-ubwc-v2-1-7ff73624635e@oss.qualcomm.com

Changes in v2:
- Changed adreno_get_param() return -ENOENT for affected params (Rob)
- Link to v1: https://patch.msgid.link/20260407-adreno-fix-ubwc-v1-1-bb2b09450b87@oss.qualcomm.com
---
 drivers/gpu/drm/msm/adreno/adreno_gpu.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/gpu/drm/msm/adreno/adreno_gpu.c b/drivers/gpu/drm/msm/adreno/adreno_gpu.c
index 66f80f2d12f9..02f60b33ea1d 100644
--- a/drivers/gpu/drm/msm/adreno/adreno_gpu.c
+++ b/drivers/gpu/drm/msm/adreno/adreno_gpu.c
@@ -424,15 +424,21 @@ int adreno_get_param(struct msm_gpu *gpu, struct msm_context *ctx,
 		*value = vm->mm_range;
 		return 0;
 	case MSM_PARAM_HIGHEST_BANK_BIT:
+		if (!adreno_gpu->ubwc_config)
+			return UERR(ENOENT, drm, "no UBWC on this platform");
 		*value = adreno_gpu->ubwc_config->highest_bank_bit;
 		return 0;
 	case MSM_PARAM_RAYTRACING:
 		*value = adreno_gpu->has_ray_tracing;
 		return 0;
 	case MSM_PARAM_UBWC_SWIZZLE:
+		if (!adreno_gpu->ubwc_config)
+			return UERR(ENOENT, drm, "no UBWC on this platform");
 		*value = adreno_gpu->ubwc_config->ubwc_swizzle;
 		return 0;
 	case MSM_PARAM_MACROTILE_MODE:
+		if (!adreno_gpu->ubwc_config)
+			return UERR(ENOENT, drm, "no UBWC on this platform");
 		*value = adreno_gpu->ubwc_config->macrotile_mode;
 		return 0;
 	case MSM_PARAM_UCHE_TRAP_BASE:

---
base-commit: 66672af7a095d89f082c5327f3b15bc2f93d558e
change-id: 20260407-adreno-fix-ubwc-6a2564710e21

Best regards,
--  
With best wishes
Dmitry

Re: [PATCH v3] drm/msm/adreno: fix userspace-triggered crash on a2xx-a4xx

[Rob Clark]

On Sat, Apr 11, 2026 at 7:59 AM Dmitry Baryshkov
<dmitry.baryshkov@oss.qualcomm.com> 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@oss.qualcomm.com>

Reviewed-by: Rob Clark <rob.clark@oss.qualcomm.com>

> ---
> Changes in v3:
> - Switched to UERR (Rob)
> - Link to v2: https://patch.msgid.link/20260407-adreno-fix-ubwc-v2-1-7ff73624635e@oss.qualcomm.com
>
> Changes in v2:
> - Changed adreno_get_param() return -ENOENT for affected params (Rob)
> - Link to v1: https://patch.msgid.link/20260407-adreno-fix-ubwc-v1-1-bb2b09450b87@oss.qualcomm.com
> ---
>  drivers/gpu/drm/msm/adreno/adreno_gpu.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/drivers/gpu/drm/msm/adreno/adreno_gpu.c b/drivers/gpu/drm/msm/adreno/adreno_gpu.c
> index 66f80f2d12f9..02f60b33ea1d 100644
> --- a/drivers/gpu/drm/msm/adreno/adreno_gpu.c
> +++ b/drivers/gpu/drm/msm/adreno/adreno_gpu.c
> @@ -424,15 +424,21 @@ int adreno_get_param(struct msm_gpu *gpu, struct msm_context *ctx,
>                 *value = vm->mm_range;
>                 return 0;
>         case MSM_PARAM_HIGHEST_BANK_BIT:
> +               if (!adreno_gpu->ubwc_config)
> +                       return UERR(ENOENT, drm, "no UBWC on this platform");
>                 *value = adreno_gpu->ubwc_config->highest_bank_bit;
>                 return 0;
>         case MSM_PARAM_RAYTRACING:
>                 *value = adreno_gpu->has_ray_tracing;
>                 return 0;
>         case MSM_PARAM_UBWC_SWIZZLE:
> +               if (!adreno_gpu->ubwc_config)
> +                       return UERR(ENOENT, drm, "no UBWC on this platform");
>                 *value = adreno_gpu->ubwc_config->ubwc_swizzle;
>                 return 0;
>         case MSM_PARAM_MACROTILE_MODE:
> +               if (!adreno_gpu->ubwc_config)
> +                       return UERR(ENOENT, drm, "no UBWC on this platform");
>                 *value = adreno_gpu->ubwc_config->macrotile_mode;
>                 return 0;
>         case MSM_PARAM_UCHE_TRAP_BASE:
>
> ---
> base-commit: 66672af7a095d89f082c5327f3b15bc2f93d558e
> change-id: 20260407-adreno-fix-ubwc-6a2564710e21
>
> Best regards,
> --
> With best wishes
> Dmitry
>

Claude review: drm/msm/adreno: fix userspace-triggered crash on a2xx-a4xx

[Claude Code Review Bot]

Overall Series Review

Subject: drm/msm/adreno: fix userspace-triggered crash on a2xx-a4xx
Author: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Patches: 2
Reviewed: 2026-04-12T08:59:45.879716

---

This is a single patch (v3) fixing a **userspace-triggerable NULL pointer dereference** on Adreno a2xx through a4xx GPUs. The bug was introduced by commit `a452510aad53` which refactored UBWC configuration into a common struct and added a pointer (`ubwc_config`) that gets dereferenced in `adreno_get_param()` — but a2xx, a3xx, and a4xx GPUs never set this pointer since they predate UBWC support.

The fix is correct, minimal, and well-targeted. The approach of returning `-ENOENT` via the `UERR()` macro is consistent with how other unsupported parameter queries are handled in this function and matches the v2/v3 review feedback from Rob Clark.

**Verdict: Looks good.**

---
Generated by Claude Code Patch Reviewer

Claude review: drm/msm/adreno: fix userspace-triggered crash on a2xx-a4xx

[Claude Code Review Bot]

Patch Review

**Problem analysis:** Confirmed correct. The kernel source tree shows:
- `a5xx_gpu.c` sets `adreno_gpu->ubwc_config = &adreno_gpu->_ubwc_config` (line 1778)
- `a6xx_gpu.c` sets `gpu->ubwc_config = &gpu->_ubwc_config` (line 807)
- `a2xx_gpu.c`, `a3xx_gpu.c`, `a4xx_gpu.c` never touch `ubwc_config` — the pointer remains NULL from `kzalloc`

Since `MSM_PARAM_HIGHEST_BANK_BIT` (0x10), `MSM_PARAM_UBWC_SWIZZLE` (0x12), and `MSM_PARAM_MACROTILE_MODE` (0x13) are all UAPI params, any userspace program can query them and trigger the NULL dereference on pre-a5xx hardware.

**Code review:**

The three guard clauses are identical in structure and correct:

```c
case MSM_PARAM_HIGHEST_BANK_BIT:
	if (!adreno_gpu->ubwc_config)
		return UERR(ENOENT, drm, "no UBWC on this platform");
	*value = adreno_gpu->ubwc_config->highest_bank_bit;
	return 0;
```

- The `UERR(ENOENT, ...)` macro expands to `DRM_DEV_DEBUG_DRIVER(...)` followed by returning `-ENOENT`. This is appropriate — `ENOENT` signals "this parameter doesn't exist on this hardware" which is semantically correct and matches the review feedback.
- The debug message is helpful for userspace developers without being noisy (it's `DEBUG_DRIVER` level, not a warning).
- All three UBWC-related params are covered: `HIGHEST_BANK_BIT`, `UBWC_SWIZZLE`, and `MACROTILE_MODE`. No UBWC-related params are missed.

**No issues found.** The patch is minimal, correct, has proper `Fixes:` tag, and addresses the review feedback from v1/v2. 

Reviewed-by worthy.

---
Generated by Claude Code Patch Reviewer