{"cve":"CVE-2025-40288","nvd":{"published":"2025-12-06T22:15:57.067","modified":"2026-10-14T22:10:00.210","status":"Deferred","description":"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->bdev` (the backing device pointer within the manager) remains\nuninitialized (NULL) on APUs—since APUs lack dedicated VRAM and do not fully\nset up VRAM manager structures. When `ttm_resource_manager_usage()` attempts to\nacquire `man->bdev->lru_lock`, it dereferences the NULL `man->bdev`, 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—skipping 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->bdev` 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's design by using its native helper function,\n- Preserves correct behavior for discrete GPUs (which have fully initialized\n  `man->bdev` and pass the `ttm_resource_manager_used()` check).\n\nv4: use ttm_resource_manager_used(&adev->mman.vram_mgr.manager) instead of checking the adev->gmc.is_app_apu flag (Christian)","cvss_v4":null,"cvss_v3":null,"cwes":[],"references":["https://git.kernel.org/stable/c/070bdce18fb12a49eb9c421e57df17d2ad29bf5f","https://git.kernel.org/stable/c/1243e396148a65bb6c42a2b70fe43e50c16c494f","https://git.kernel.org/stable/c/43aa61c18a3a45042b098b7a1186ffb29364002c","https://git.kernel.org/stable/c/883f309add55060233bf11c1ea6947140372920f","https://git.kernel.org/stable/c/e70113b741ba253886cd71dbadfe3ea444bb2f5c"],"products":[],"source":"nvd","synced_at":"2026-10-19T22:16:40.427100871+00:00"},"epss":{"cve":"CVE-2025-40288","score":0.00186,"percentile":0.08097,"date":"2026-10-25"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}