Re: [PATCH] iommu/mediatek: Remove a unnecessary checking for larbid

[AngeloGioacchino Del Regno]

Il 05/07/23 10:26, Robin Murphy ha scritto:
> On 2023-07-05 07:49, Yong Wu (吴勇) wrote:
> > On Tue, 2023-07-04 at 14:19 +0200, AngeloGioacchino Del Regno wrote:
> > > External email : Please do not click links or open attachments until
> > > you have verified the sender or the content.
> > >   Il 04/07/23 13:56, Yong Wu ha scritto:
> > > > Fix a coverity issue:
> > > >
> > > > > > assignment: Assigning: larbid = (fwspec->ids[0] >> 5) & 0x1fU.
> > > > larbid = MTK_M4U_TO_LARB(fwspec->ids[0]);
> > > > > > between: At condition larbid >= 32U, the value of larbid must be
> > > between
> > > > > > 0 and 31.
> > > > > > dead_error_condition: The condition larbid >= 32U cannot be true.
> > > > if (larbid >= MTK_LARB_NR_MAX)
> > > > > > CID 11306470 (#1 of 1): Logically dead code (DEADCODE)
> > > > > > dead_error_line: Execution cannot reach this statement:
> > > > > > return ERR_PTR(-22L);
> > > >           return ERR_PTR(-EINVAL);
> > > >
> > > > The checking "if (larbid >= MTK_LARB_NR_MAX)" is unnecessary.
> > >
> > > I agree with the coverity tool in that after the transformation
> > > (going through
> > > the definition of MTK_M4U_TO_LARB) the check is pointless, but I
> > > think that the
> > > right fix here is to check for validity of fwspec->ids[0] instead of
> > > simply
> > > removing validation.
> > >
> > > Having no validation after mtk_iommu_probe_device() is fine, but
> > > that's
> > > because we assume that *this* function performs all validation steps.
> >
> > There already is validation code at the point later in this function.
> >
> > "if (!larbdev) return ERR_PTR(-EINVAL);" //if the larbid is invalid.
> >
> > This patch just removes a deadcode.
>
> Right, if the fwspec value was out of range then the truncated value might happen 
> to map to a valid LARB, but then the fwspec could equally have an in-range value 
> for a valid (but incorrect) LARB; in general a driver can't validate the overall 
> correctness of data from the DT (and if it could, that data wouldn't need to be in 
> the DT anyway).
>
>  From the history, the intent of this check doesn't appear to have been anything 
> other than protecting the dereference of the data->larb_imu array, and it's never 
> had any functional effect, so we don't lose anything by removing it. FWIW,
>
> Reviewed-by: Robin Murphy <robin.murphy@xxxxxxx>

Yong, you're right. My bad for not noticing the later validation code.

Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@xxxxxxxxxxxxx>

> Cheers,
> Robin.
>
> > > Regards,
> > > Angelo
> > >
> > > > Signed-off-by: Yong Wu <yong.wu@xxxxxxxxxxxx>
> > > > ---
> > > > Rebase on v6.4-rc1.
> > > > ---
> > > >    drivers/iommu/mtk_iommu.c | 3 ---
> > > >    1 file changed, 3 deletions(-)
> > > >
> > > > diff --git a/drivers/iommu/mtk_iommu.c b/drivers/iommu/mtk_iommu.c
> > > > index aecc7d154f28..67caa90b481b 100644
> > > > --- a/drivers/iommu/mtk_iommu.c
> > > > +++ b/drivers/iommu/mtk_iommu.c
> > > > @@ -838,9 +838,6 @@ static struct iommu_device
> > > *mtk_iommu_probe_device(struct device *dev)
> > > >     * All the ports in each a device should be in the same larbs.
> > > >     */
> > > >    larbid = MTK_M4U_TO_LARB(fwspec->ids[0]);
> > > > -if (larbid >= MTK_LARB_NR_MAX)
> > > > -return ERR_PTR(-EINVAL);
> > > > -
> > > >    for (i = 1; i < fwspec->num_ids; i++) {
> > > >    larbidx = MTK_M4U_TO_LARB(fwspec->ids[i]);
> > > >    if (larbid != larbidx) {