PoC DF-1593: rv515.c debugfs ga_info triggers GPU reset on read

Class: DoS / availability (unprivileged GPU reset) Cited site: sys/dev/drm/radeon/rv515.c:250-263,286

Reproduction status

HW/module gated — cannot be live-triggered on the audit QEMU guest.

The audit guest has only virtio + PIIX3 PCI devices (pciconf -lv shows no AMD/Intel GPU, no ath NIC, no AdvanSys SCSI, no mfi/tws/mrsas RAID, etc.), so the cited code path is not reachable at runtime on this guest.

The bug is confirmed at the source level by tracing the cited path:line in sys/dev/drm/radeon/rv515.c and confirming the vulnerable code is present in the master DEV kernel tree. The fix.diff in this folder is validated to apply cleanly and compile under -Werror (see VERDICT.md).

Mechanism

rv515_debugfs_ga_info show() callback calls radeon_asic_reset(rdev) unconditionally between two register reads. Registered via radeon_debugfs_add_files at 286; DRM info-list entries default S_IFREG|S_IRUGO world-readable. Any local user who cat /sys/kernel/debug/dri/N/rv515_ga_info triggers full GPU reset: aborts CP ring, drops in-flight DMA, blanks displays, crashes X/Wayland. Repeatable indefinitely. Sibling ASICs do NOT call asic_reset in their ga_info handlers.

Realistic impact ceiling (on suitable HW)

unprivileged DoS of the GPU subsystem (and any GPU-accelerated process)

Fix

Drop the radeon_asic_reset(rdev) call from rv515_debugfs_ga_info; sibling handlers do not reset.

See fix.diff for the git-apply-able patch.

How to validate the fix

scp -F dfbsd-qemu/config fix.diff dfbsd:/root/DF-1593.diff
ssh -F dfbsd-qemu/config dfbsd 'cd /usr/src && patch -p1 --forward < /root/DF-1593.diff'
ssh -F dfbsd-qemu/config dfbsd 'cd /usr/src && make -j6 nativekernel KERNCONF=X86_64_GENERIC'
# rc=0 expected; see fix_apply.log + fix_build.log in this folder.

VERDICT — DF-1593: rv515.c debugfs ga_info triggers GPU reset on read

Verdict

INCONCLUSIVE (HW/module gated) — source-level confirmed, fix validated.

The bug is real and present in master DEV source at sys/dev/drm/radeon/rv515.c:250-263,286, but the affected driver attaches only to hardware not present in the audit QEMU guest (only virtio+PIIX3 PCI devices, no AMD/Intel GPUs, no ath NICs, no AdvanSys SCSI, no mfi/tws/mrsas RAID, etc.), so it cannot be live-triggered here. The fix.diff applies cleanly and the patched kernel compiles with -Werror (combined build rc=0; see fix_apply.log).

Mechanism (cited path → primitive → effect)

rv515_debugfs_ga_info show() callback calls radeon_asic_reset(rdev) unconditionally between two register reads. Registered via radeon_debugfs_add_files at 286; DRM info-list entries default S_IFREG|S_IRUGO world-readable. Any local user who cat /sys/kernel/debug/dri/N/rv515_ga_info triggers full GPU reset: aborts CP ring, drops in-flight DMA, blanks displays, crashes X/Wayland. Repeatable indefinitely. Sibling ASICs do NOT call asic_reset in their ga_info handlers.

Reachability on this guest

No — sys/dev/drm/radeon/rv515.c:250-263 is in a driver/module that only attaches to hardware absent from the audit guest. The trigger requires the relevant PCI device (or, for VBIOS-driven GPU paths, the actual GPU + a crafted VBIOS loaded by root or via VFIO passthrough).

Phase 6 — escalation potential

This is a DoS / availability primitive. On real hardware it could be triggered by an unprivileged user (via crafted packets for the NIC findings, via DRM ioctls for the GPU findings, via CAM/pass for the SCSI findings). On this guest there is no live primitive to convert. Per Phase 6 rules this is the "dead/unreachable at runtime on this guest" hard blocker; the primitive is proven at the source/harness level (the cited path:line is real and unfixed in master).

Realistic impact ceiling on suitable HW: unprivileged DoS of the GPU subsystem (and any GPU-accelerated process).

Phase 8 — fix validation

fix.diff is a minimal, targeted fix at the root cause confirmed above.

• Applied cleanly with patch -p1 --forward (verified in fix_apply.log).
• Compiled with -Werror as part of the combined make -j6 nativekernel KERNCONF=X86_64_GENERIC build (kernel build rc=0; see manifest.json).
• For HW-gated findings the patched code path is not exercisable on this guest, so the fix is validated at the apply + compile level only.

Fix approach: Drop the radeon_asic_reset(rdev) call from rv515_debugfs_ga_info; sibling handlers do not reset.

PoC changes

Source-level confirmation only; no userspace harness written because the bug cannot be exercised on this guest without the relevant HW. The placeholder build.sh/run.sh echo pointers to VERDICT.md and the module/kernel rebuild path.