In the Linux kernel, the following vulnerability has been resolved:
drm/amdgpu: Fix NULL pointer dereference in VRAM logic for APU devices
Previously, APU platforms (and other scenarios with uninitialized VRAM managers)
triggered a NULL pointer dereference in `ttm_resource_manager_usage()`. The root
cause is not that the `struct ttm_resource_manager *man` pointer itself is NULL,
but that `man->bdev` (the backing device pointer within the manager) remains
uninitialized (NULL) on APUs—since APUs lack dedicated VRAM and do not fully
set up VRAM manager structures. When `ttm_resource_manager_usage()` attempts to
acquire `man->bdev->lru_lock`, it dereferences the NULL `man->bdev`, leading to
a kernel OOPS.
1. **amdgpu_cs.c**: Extend the existing bandwidth control check in
`amdgpu_cs_get_threshold_for_moves()` to include a check for
`ttm_resource_manager_used()`. If the manager is not used (uninitialized
`bdev`), return 0 for migration thresholds immediately—skipping VRAM-specific
logic that would trigger the NULL dereference.
2. **amdgpu_kms.c**: Update the `AMDGPU_INFO_VRAM_USAGE` ioctl and memory info
reporting to use a conditional: if the manager is used, return the real VRAM
usage; otherwise, return 0. This avoids accessing `man->bdev` when it is
NULL.
3. **amdgpu_virt.c**: Modify the vf2pf (virtual function to physical function)
data write path. Use `ttm_resource_manager_used()` to check validity: if the
manager is usable, calculate `fb_usage` from VRAM usage; otherwise, set
`fb_usage` to 0 (APUs have no discrete framebuffer to report).
This approach is more robust than APU-specific checks because it:
- Works for all scenarios where the VRAM manager is uninitialized (not just APUs),
- Aligns with TTM's design by using its native helper function,
- Preserves correct behavior for discrete GPUs (which have fully initialized
`man->bdev` and pass the `ttm_resource_manager_used()` check).
v4: use ttm_resource_manager_used(&adev->mman.vram_mgr.manager) instead of checking the adev->gmc.is_app_apu flag (Christian)
drm/amdgpu: Fix NULL pointer dereference in VRAM logic for APU devices
Previously, APU platforms (and other scenarios with uninitialized VRAM managers)
triggered a NULL pointer dereference in `ttm_resource_manager_usage()`. The root
cause is not that the `struct ttm_resource_manager *man` pointer itself is NULL,
but that `man->bdev` (the backing device pointer within the manager) remains
uninitialized (NULL) on APUs—since APUs lack dedicated VRAM and do not fully
set up VRAM manager structures. When `ttm_resource_manager_usage()` attempts to
acquire `man->bdev->lru_lock`, it dereferences the NULL `man->bdev`, leading to
a kernel OOPS.
1. **amdgpu_cs.c**: Extend the existing bandwidth control check in
`amdgpu_cs_get_threshold_for_moves()` to include a check for
`ttm_resource_manager_used()`. If the manager is not used (uninitialized
`bdev`), return 0 for migration thresholds immediately—skipping VRAM-specific
logic that would trigger the NULL dereference.
2. **amdgpu_kms.c**: Update the `AMDGPU_INFO_VRAM_USAGE` ioctl and memory info
reporting to use a conditional: if the manager is used, return the real VRAM
usage; otherwise, return 0. This avoids accessing `man->bdev` when it is
NULL.
3. **amdgpu_virt.c**: Modify the vf2pf (virtual function to physical function)
data write path. Use `ttm_resource_manager_used()` to check validity: if the
manager is usable, calculate `fb_usage` from VRAM usage; otherwise, set
`fb_usage` to 0 (APUs have no discrete framebuffer to report).
This approach is more robust than APU-specific checks because it:
- Works for all scenarios where the VRAM manager is uninitialized (not just APUs),
- Aligns with TTM's design by using its native helper function,
- Preserves correct behavior for discrete GPUs (which have fully initialized
`man->bdev` and pass the `ttm_resource_manager_used()` check).
v4: use ttm_resource_manager_used(&adev->mman.vram_mgr.manager) instead of checking the adev->gmc.is_app_apu flag (Christian)
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References
History
Sat, 06 Dec 2025 22:00:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Description | In the Linux kernel, the following vulnerability has been resolved: drm/amdgpu: Fix NULL pointer dereference in VRAM logic for APU devices Previously, APU platforms (and other scenarios with uninitialized VRAM managers) triggered a NULL pointer dereference in `ttm_resource_manager_usage()`. The root cause is not that the `struct ttm_resource_manager *man` pointer itself is NULL, but that `man->bdev` (the backing device pointer within the manager) remains uninitialized (NULL) on APUs—since APUs lack dedicated VRAM and do not fully set up VRAM manager structures. When `ttm_resource_manager_usage()` attempts to acquire `man->bdev->lru_lock`, it dereferences the NULL `man->bdev`, leading to a kernel OOPS. 1. **amdgpu_cs.c**: Extend the existing bandwidth control check in `amdgpu_cs_get_threshold_for_moves()` to include a check for `ttm_resource_manager_used()`. If the manager is not used (uninitialized `bdev`), return 0 for migration thresholds immediately—skipping VRAM-specific logic that would trigger the NULL dereference. 2. **amdgpu_kms.c**: Update the `AMDGPU_INFO_VRAM_USAGE` ioctl and memory info reporting to use a conditional: if the manager is used, return the real VRAM usage; otherwise, return 0. This avoids accessing `man->bdev` when it is NULL. 3. **amdgpu_virt.c**: Modify the vf2pf (virtual function to physical function) data write path. Use `ttm_resource_manager_used()` to check validity: if the manager is usable, calculate `fb_usage` from VRAM usage; otherwise, set `fb_usage` to 0 (APUs have no discrete framebuffer to report). This approach is more robust than APU-specific checks because it: - Works for all scenarios where the VRAM manager is uninitialized (not just APUs), - Aligns with TTM's design by using its native helper function, - Preserves correct behavior for discrete GPUs (which have fully initialized `man->bdev` and pass the `ttm_resource_manager_used()` check). v4: use ttm_resource_manager_used(&adev->mman.vram_mgr.manager) instead of checking the adev->gmc.is_app_apu flag (Christian) | |
| Title | drm/amdgpu: Fix NULL pointer dereference in VRAM logic for APU devices | |
| First Time appeared |
Linux
Linux linux Kernel |
|
| CPEs | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Linux
Linux linux Kernel |
|
| References |
|
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Projects
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MITRE
Status: PUBLISHED
Assigner: Linux
Published:
Updated: 2025-12-06T21:51:14.440Z
Reserved: 2025-04-16T07:20:57.184Z
Link: CVE-2025-40288
Vulnrichment
No data.
NVD
Status : Received
Published: 2025-12-06T22:15:57.067
Modified: 2025-12-06T22:15:57.067
Link: CVE-2025-40288
Redhat
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OpenCVE Enrichment
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Weaknesses
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