Findings

CVE-2025-40288

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 (a…

Published Dec 6, 2025 · updated Oct 14, 2026

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 . The root cause is not that the pointer itself is NULL, but that (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 attempts to acquire , it dereferences the NULL , leading to a kernel OOPS. 1. **amdgpu_cs.c**: Extend the existing bandwidth control check in to include a check for . If the manager is not used (uninitialized ), return 0 for migration thresholds immediately—skipping VRAM-specific logic that would trigger the NULL dereference. 2. **amdgpu_kms.c**: Update the 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 when it is NULL. 3. **amdgpu_virt.c**: Modify the vf2pf (virtual function to physical function) data write path. Use to check validity: if the manager is usable, calculate from VRAM usage; otherwise, set 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 and pass the check). v4: use ttm_resource_manager_used(&adev->mman.vram_mgr.manager) instead of checking the adev->gmc.is_app_apu flag (Christian)