Re: [PATCH] drm/amdgpu/atom: do not dereference NULL vbios string pointer

[Alex Deucher]

On Mon, Nov 9, 2026 at 4:41 AM Noah Weinberger
<NoahWeinberger2003@xxxxxxxxx> wrote:
>
> Hello,
>
> In atom_get_vbios_pn(), when the part-number string is empty and
> atom_find_str_in_rom() cannot find the ATOMBIOS anchor, the fallback
> computes NULL + sizeof(BIOS_ATOM_PREFIX) - 1, i.e. (unsigned char *)8:
>
>     vbios_str = atom_find_str_in_rom(ctx, BIOS_ATOM_PREFIX, 3, 1024, 64);
>     if (vbios_str == NULL)
>             vbios_str += sizeof(BIOS_ATOM_PREFIX) - 1;
>
> The subsequent range check is false for a near-NULL pointer, so the
> value survives and *vbios_str dereferences address 8 - a NULL-page oops
> during probe with a malformed VBIOS that passes the magic checks. The
> recent hardening of the neighboring date/version/build helpers closed
> their OOB reads; this fallback path was left intact.
>
> Simply leave the part number empty when the anchor is not found.
>
> Affected version/commit: mainline fa4ad798f6f681031775266044ba1b0cf3c670bd (v7.4-rc1, 2026-11-07), drivers/gpu/drm/amd/amdgpu/atom.c:1491-1503 (atom_get_vbios_pn).
> Pointer-arithmetic-on-NULL is pre-existing; this window's hardening series made it the sole fallback outcome.
>
> This was found during an assisted (AI-supported) static source review of
> mainline fa4ad798f6f681031775266044ba1b0cf3c670bd (v7.4-rc1, 2026-11-07); every code path cited below was re-verified by the
> reporter against that tree. The patch below has NOT been compiled and has
> NOT been runtime tested, and no reproducer was produced - the triggering
> conditions are described above instead. Please treat this as a report for
> verification rather than a battle-tested fix.
>
> Reported-by: Noah Weinberger <noahweinberger2003@xxxxxxxxx>

Missing your Signed-off-by.

Alex

> ---
> diff --git a/drivers/gpu/drm/amd/amdgpu/atom.c b/drivers/gpu/drm/amd/amdgpu/atom.c
> index 1a599d5..7598606 100644
> --- a/drivers/gpu/drm/amd/amdgpu/atom.c
> +++ b/drivers/gpu/drm/amd/amdgpu/atom.c
> @@ -1493,8 +1493,6 @@ static void atom_get_vbios_pn(struct atom_context *ctx)
>
>         if (vbios_str == NULL || *vbios_str == 0) {
>                 vbios_str = atom_find_str_in_rom(ctx, BIOS_ATOM_PREFIX, 3, 1024, 64);
> -               if (vbios_str == NULL)
> -                       vbios_str += sizeof(BIOS_ATOM_PREFIX) - 1;
>                 if (vbios_str >= p_rom + ctx->bios_size)
>                         vbios_str = NULL;
>         }
>