[PATCH] drm/nouveau: fix off by one in BIOS boundry checking

[Karol Herbst]

On Sat, Jan 22, 2022 at 11:44 AM Nick Lopez <github at glowingmonkey.org> wrote:
>
> Bounds checking when parsing init scripts embedded in the BIOS reject
> access to the last byte. This causes driver initialization to fail on
> Apple eMac's with GeForce 2 MX GPUs, leaving the system with no working
> console.
>
> This is probably only seen on OpenFirmware machines like PowerPC Macs
> because the BIOS image provides by OF is only the used parts of the ROM,
> not a power-of-two blocks read from PCI directly so PCs always have
> empty bytes at the end that are never accesseed.
>

small typo nitpicks: provided and accessed

Also, I think it makes sense to add

Fixes: 4d4e9907ff572 "drm/nouveau/bios: guard against out-of-bounds
accesses to image"
Cc: <stable at vger.kernel.org> # v4.10+

so it gets automatically backported to applicable stable kernels

Anyway, whoever picks the patch can make those adjustments as well.

Reviewed-by: Karol Herbst <kherbst at redhat.com>


> Signed-off-by: Nick Lopez <github at glowingmonkey.org>
> ---
>  drivers/gpu/drm/nouveau/nvkm/subdev/bios/base.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/nouveau/nvkm/subdev/bios/base.c b/drivers/gpu/drm/nouveau/nvkm/subdev/bios/base.c
> index d0f52d59fc2f..64e423dddd9e 100644
> --- a/drivers/gpu/drm/nouveau/nvkm/subdev/bios/base.c
> +++ b/drivers/gpu/drm/nouveau/nvkm/subdev/bios/base.c
> @@ -38,7 +38,7 @@ nvbios_addr(struct nvkm_bios *bios, u32 *addr, u8 size)
>                 *addr += bios->imaged_addr;
>         }
>
> -       if (unlikely(*addr + size >= bios->size)) {
> +       if (unlikely(*addr + size > bios->size)) {
>                 nvkm_error(&bios->subdev, "OOB %d %08x %08x\n", size, p, *addr);
>                 return false;
>         }
> --
> 2.30.2
>