Nouveau - Jan 2022 - [PATCH] drm/nouveau: fix off by one in BIOS boundry checking

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.

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

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
>