Re: [PATCH] mtd: onenand_base: Avoid fall-through warnings
From: Kees Cook
Date: Wed May 22 2019 - 17:33:03 EST
Sorry for being late to speaking up on this. I missed something in the
code the first time I read the thread, that now stood out to me. Notes
below...
On Wed, May 22, 2019 at 01:04:46PM -0500, Gustavo A. R. Silva wrote:
> diff --git a/drivers/mtd/nand/onenand/onenand_base.c b/drivers/mtd/nand/onenand/onenand_base.c
> index f41d76248550..6cf4df9f8c01 100644
> --- a/drivers/mtd/nand/onenand/onenand_base.c
> +++ b/drivers/mtd/nand/onenand/onenand_base.c
> @@ -3280,12 +3280,14 @@ static void onenand_check_features(struct mtd_info *mtd)
Reverse-order review, second hunk first:
> case ONENAND_DEVICE_DENSITY_2Gb:
> /* 2Gb DDP does not have 2 plane */
> if (!ONENAND_IS_DDP(this))
> this->options |= ONENAND_HAS_2PLANE;
> this->options |= ONENAND_HAS_UNLOCK_ALL;
> + /* Fall through - ? */
>
> case ONENAND_DEVICE_DENSITY_1Gb:
> /* A-Die has all block unlock */
So, I think the ONENAND_DEVICE_DENSITY_2Gb should be a "break". Though,
actually, it doesn't matter:
case ONENAND_DEVICE_DENSITY_2Gb:
/* 2Gb DDP does not have 2 plane */
if (!ONENAND_IS_DDP(this))
this->options |= ONENAND_HAS_2PLANE;
this->options |= ONENAND_HAS_UNLOCK_ALL;
case ONENAND_DEVICE_DENSITY_1Gb:
/* A-Die has all block unlock */
if (process)
this->options |= ONENAND_HAS_UNLOCK_ALL;
break;
Falling through from ONENAND_DEVICE_DENSITY_2Gb to
ONENAND_DEVICE_DENSITY_1Gb will actually have no side-effects:
ONENAND_HAS_UNLOCK_ALL was unconditionally set in ..._2Gb, so there is
no reason to fall through to ..._1Gb. (But falling through is harmless.)
Now the first hunk:
> if ((this->version_id & 0xf) == 0xe)
> this->options |= ONENAND_HAS_NOP_1;
> }
> + /* Fall through - ? */
>
case ONENAND_DEVICE_DENSITY_4Gb:
if (ONENAND_IS_DDP(this))
this->options |= ONENAND_HAS_2PLANE;
else if (numbufs == 1) {
this->options |= ONENAND_HAS_4KB_PAGE;
this->options |= ONENAND_HAS_CACHE_PROGRAM;
/*
* There are two different 4KiB pagesize chips
* and no way to detect it by H/W config values.
*
* To detect the correct NOP for each chips,
* It should check the version ID as workaround.
*
* Now it has as following
* KFM4G16Q4M has NOP 4 with version ID 0x0131
* KFM4G16Q5M has NOP 1 with versoin ID 0x013e
*/
if ((this->version_id & 0xf) == 0xe)
this->options |= ONENAND_HAS_NOP_1;
}
Falling through from ONENAND_DEVICE_DENSITY_4Gb to
ONENAND_DEVICE_DENSITY_2Gb looks like it would mean that
ONENAND_HAS_2PLANE would be unconditionally set for ...4Gb, which seems
very strange to expect:
if (ONENAND_IS_DDP(this))
this->options |= ONENAND_HAS_2PLANE;
...
if (!ONENAND_IS_DDP(this))
this->options |= ONENAND_HAS_2PLANE;
However! This happens later:
if (ONENAND_IS_4KB_PAGE(this))
this->options &= ~ONENAND_HAS_2PLANE;
i.e. falling through to ...2Gb (which sets ONENAND_HAS_2PLANE) has no
effect because when ONENAND_HAS_2PLANE isn't set (numbufs == 1), it gets
_cleared_ by the above code due to ONENAND_HAS_4KB_PAGE getting set:
#define ONENAND_IS_4KB_PAGE(this) \
(this->options & ONENAND_HAS_4KB_PAGE)
Unfortunately, though, it's less clear about ONENAND_HAS_UNLOCK_ALL,
which is getting set unconditionally for ...4Gb currently (due to the
fallthrough to ...2Gb). However, this happens later:
if (FLEXONENAND(this)) {
this->options &= ~ONENAND_HAS_CONT_LOCK;
this->options |= ONENAND_HAS_UNLOCK_ALL;
}
...
#define FLEXONENAND(this) \
(this->device_id & DEVICE_IS_FLEXONENAND)
So it's possible this fall through has no effect (are all 4Gb density
devices also FLEXONENAND devices?)
Setting a "break" after 4Gb may remove ONENAND_HAS_UNLOCK_ALL in the
!FLEXONENAND(this) case. Does anyone have real hardware to test with?
Thoughts?
--
Kees Cook