# VERDICT — DF-1559: i915_cmd_parser signed-int min_t -> giant memcpy

## Verdict

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

The bug is real and present in master DEV source at `sys/dev/drm/i915/i915_cmd_parser.c:1104,1109, 2228`, 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)

i915_cmd_parser copy-batch loop: int len = min_t(int, batch_len, PAGE_SIZE-offset). batch_len is u32 from user EXECBUFFER2 args->batch_len, bounded only by batch->size-batch_start_offset (object creation allows sizes up to INT_MAX<<PAGE_SHIFT). For batch_len>=0x80000000: (int)0x80000000=INT_MIN < positive PAGE_SIZE -> len becomes INT_MIN=-2147483648. memcpy(ptr, src+offset, len) promotes to size_t 0xFFFFFFFF80000000 on LP64 -> massive write past shadow WB vmap into kernel vm.

## Reachability on this guest

No — `sys/dev/drm/i915/i915_cmd_parser.c:1104` 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 Heap overflow write via signedness confusion 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: **massive kernel memory corruption -> panic or potential privilege escalation**.

## 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: Reject batch_len > INT_MAX before the min_t(int, ...) loop body.

## 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.