fkie_cve-2025-40288
Vulnerability from fkie_nvd
Published
2025-12-06 22:15
Modified
2025-12-08 18:26
Severity ?
Summary
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)
References
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/070bdce18fb12a49eb9c421e57df17d2ad29bf5f
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/1243e396148a65bb6c42a2b70fe43e50c16c494f
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/43aa61c18a3a45042b098b7a1186ffb29364002c
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/883f309add55060233bf11c1ea6947140372920f
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/e70113b741ba253886cd71dbadfe3ea444bb2f5c
Impacted products
Vendor Product Version


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{
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\ndrm/amdgpu: Fix NULL pointer dereference in VRAM logic for APU devices\n\nPreviously, APU platforms (and other scenarios with uninitialized VRAM managers)\ntriggered a NULL pointer dereference in `ttm_resource_manager_usage()`. The root\ncause is not that the `struct ttm_resource_manager *man` pointer itself is NULL,\nbut that `man-\u003ebdev` (the backing device pointer within the manager) remains\nuninitialized (NULL) on APUs\u2014since APUs lack dedicated VRAM and do not fully\nset up VRAM manager structures. When `ttm_resource_manager_usage()` attempts to\nacquire `man-\u003ebdev-\u003elru_lock`, it dereferences the NULL `man-\u003ebdev`, leading to\na kernel OOPS.\n\n1. **amdgpu_cs.c**: Extend the existing bandwidth control check in\n   `amdgpu_cs_get_threshold_for_moves()` to include a check for\n   `ttm_resource_manager_used()`. If the manager is not used (uninitialized\n   `bdev`), return 0 for migration thresholds immediately\u2014skipping VRAM-specific\n   logic that would trigger the NULL dereference.\n\n2. **amdgpu_kms.c**: Update the `AMDGPU_INFO_VRAM_USAGE` ioctl and memory info\n   reporting to use a conditional: if the manager is used, return the real VRAM\n   usage; otherwise, return 0. This avoids accessing `man-\u003ebdev` when it is\n   NULL.\n\n3. **amdgpu_virt.c**: Modify the vf2pf (virtual function to physical function)\n   data write path. Use `ttm_resource_manager_used()` to check validity: if the\n   manager is usable, calculate `fb_usage` from VRAM usage; otherwise, set\n   `fb_usage` to 0 (APUs have no discrete framebuffer to report).\n\nThis approach is more robust than APU-specific checks because it:\n- Works for all scenarios where the VRAM manager is uninitialized (not just APUs),\n- Aligns with TTM\u0027s design by using its native helper function,\n- Preserves correct behavior for discrete GPUs (which have fully initialized\n  `man-\u003ebdev` and pass the `ttm_resource_manager_used()` check).\n\nv4: use ttm_resource_manager_used(\u0026adev-\u003emman.vram_mgr.manager) instead of checking the adev-\u003egmc.is_app_apu flag (Christian)"
    }
  ],
  "id": "CVE-2025-40288",
  "lastModified": "2025-12-08T18:26:49.133",
  "metrics": {},
  "published": "2025-12-06T22:15:57.067",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/070bdce18fb12a49eb9c421e57df17d2ad29bf5f"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/1243e396148a65bb6c42a2b70fe43e50c16c494f"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/43aa61c18a3a45042b098b7a1186ffb29364002c"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/883f309add55060233bf11c1ea6947140372920f"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/e70113b741ba253886cd71dbadfe3ea444bb2f5c"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Awaiting Analysis"
}


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