# VERDICT -- DF-1388

## Verdict: INCONCLUSIVE at runtime; source bug CONFIRMED; fix COMPILE-VALIDATED

**Citations confirmed:**
  - sys/dev/drm/i915/intel_bios.c:83
  - sys/dev/drm/i915/intel_bios.c:91
  - sys/dev/drm/i915/intel_bios.c:93
  - sys/dev/drm/i915/intel_bios.c:96

### Is the bug real? -- YES (source trace)

find_section() does `if (index + current_size > total) return NULL;`. `index` is
    `int`, `current_size` is `u32`. In C's normal arithmetic, `int + u32` promotes
the int to u32 and the sum wraps mod 2^32. With current_size=0xFFFFFFFF and
index=6, the sum wraps to 5, which is < total => block accepted even though it
extends past the BDB. find_panel_sequence_block :864 then re-reads the size as
`total` and parses past the BDB. MIPI v3 _get_blocksize is the only path that
returns u32; it returns the value from `*((const u32 *)(block_base + 4))` which
is attacker-VBT-controlled. Reached via GPU ROM or OpRegion.

### Can it be reproduced on this guest? -- NO (hardware-gated)

No Intel integrated GPU in PCI list (only QEMU stdvga 0x11111234); i915.ko not loaded.

The i915 driver is a loadable module only (NOT in `X86_64_GENERIC`), is not loaded, and cannot be `kldload`'d by an unprivileged user (kldload is root-only). Even loaded, it would not attach without the hardware.
Therefore the vulnerable code is unreachable at runtime here. Because the sinks are device-integrated parsers / DRM ioctls / DMA-supplied indices / hardware-dependent paths, no userspace harness on this guest can exercise them. This is the documented valid hard-blocker "unreachable at runtime + no feasible harness"; the bug is a real latent defect with the live trigger conditions noted above.

### No escalation chain (and why that is correct here)
There is no memory-corruption primitive to escalate on this guest: the corruption sinks live entirely inside the not-attached driver behind hardware that is absent. The escalation work the audit expects (slab groom -> victim -> uid0) presupposes a reachable write primitive; here there is none on the guest. The deliverable is therefore the confirmed root-cause + a compile-validated fix.

### Fix (fix.diff) -- authored and COMPILE-VALIDATED
Rewrote overflow-safe: `if (current_size > total - index) return NULL;`.
(matches finding proposal exactly.)

The fix was applied to in-guest `/usr/src` (all hunks applied cleanly) and the
module was rebuilt with the kernel's `-Werror` flags: `cd /usr/src/sys/dev/drm/i915 && KERNCONF=X86_64_GENERIC SYSDIR=/usr/src/sys make -m /usr/src/share/mk` => rc=0 (see `build_fix.log`). No warnings or errors in the patched translation unit. The runtime before/after of the bug cannot be tested on this guest (no hardware), so fix_status is `not_testable` (diff applies + compiles; code path traced closed).

### Why not `not_reproduced` (false-positive)?
This is NOT a false positive. The cited `sys/` code is genuinely missing the guard / has the overflow / has the unclamped loop -- verified by reading the source. It is a real bug that is simply out of reach of this particular (driverless) QEMU guest.