Re: [PATCH] iommu/arm-smmu-v3: Fix undefined behavior in GBPA_UPDATE

[xenia]

On 7/1/22 17:34, Will Deacon wrote:
> On Thu, Jun 30, 2022 at 09:39:59AM +0300, Xenia Ragiadakou wrote:
> > The expression 1 << 31 results in undefined behaviour because the type of
> > integer constant 1 is (signed) int and the result of shifting 1 by 31 bits
> > is not representable in the (signed) int type.
> >
> > Change the type of 1 to unsigned int by adding the U suffix.
> >
> > Signed-off-by: Xenia Ragiadakou <burzalodowa@xxxxxxxxx>
> > ---
> >   drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
> > index cd48590ada30..44fbd499edea 100644
> > --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
> > +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
> > @@ -96,7 +96,7 @@
> >   #define CR2_E2H				(1 << 0)
> >   
> >   #define ARM_SMMU_GBPA			0x44
> > -#define GBPA_UPDATE			(1 << 31)
> > +#define GBPA_UPDATE			(1U << 31)
> There are loads of these kicking around in the kernel sources and we compile
> with -fno-strict-overflow.
>
> If you really want to change these, then let's use the BIT() macro instead,
> but I think it's really just churn.
>
> Will
Hi Will,

I thought that since in commit 587e6c10a7ce89a5924fdbeff2ec524fbd6a124b 
there was a similar fix to Q_OVERFLOW_FLAG (see below)

--- a/drivers/iommu/arm-smmu-v3.c
+++ b/drivers/iommu/arm-smmu-v3.c
@@ -183,7 +183,7 @@

 #define Q_IDX(llq, p)                  ((p) & ((1 << 
(llq)->max_n_shift) - 1))
 #define Q_WRP(llq, p)                  ((p) & (1 << (llq)->max_n_shift))
-#define Q_OVERFLOW_FLAG                        (1 << 31)
+#define Q_OVERFLOW_FLAG                        (1U << 31)
 #define Q_OVF(p)                       ((p) & Q_OVERFLOW_FLAG)
 #define Q_ENT(q, p)                    ((q)->base +                    \
                                         Q_IDX(&((q)->llq), p) *        \

then it would make sense to fix GBPA_UPDATE in the same way.

Xenia