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)
Product status
1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (git) before e70113b741ba253886cd71dbadfe3ea444bb2f5c
1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (git) before 1243e396148a65bb6c42a2b70fe43e50c16c494f
1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (git) before 43aa61c18a3a45042b098b7a1186ffb29364002c
1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (git) before 070bdce18fb12a49eb9c421e57df17d2ad29bf5f
1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (git) before 883f309add55060233bf11c1ea6947140372920f
6.1.159 (semver)
6.6.117 (semver)
6.12.59 (semver)
6.17.9 (semver)
6.18 (original_commit_for_fix)
References
git.kernel.org/...c/e70113b741ba253886cd71dbadfe3ea444bb2f5c
git.kernel.org/...c/1243e396148a65bb6c42a2b70fe43e50c16c494f
git.kernel.org/...c/43aa61c18a3a45042b098b7a1186ffb29364002c
git.kernel.org/...c/070bdce18fb12a49eb9c421e57df17d2ad29bf5f
git.kernel.org/...c/883f309add55060233bf11c1ea6947140372920f
