From: Mathieu Desnoyers
> Sent: 04 September 2023 11:24
>
> On 9/4/23 05:42, Denis Arefev wrote:
> > The value of an arithmetic expression 1 << (cpu - sdp->mynode->grplo)
> > is subject to overflow due to a failure to cast operands to a larger
> > data type before performing arithmetic
>
> The patch title should identify more precisely its context, e.g.:
>
> "srcu: Fix srcu_struct node grpmask overflow on 64-bit systems"
>
> Also, as I stated in my reply to the previous version, the patch commit
> message should describe the impact of the bug it fixes.
And is the analysis complete?
Is 1UL right for 32bit archs??
Is 64 bits even enough??
David
>
> Thanks,
>
> Mathieu
>
>
> >
> > Found by Linux Verification Center (linuxtesting.org) with SVACE.
> >
> > Signed-off-by: Denis Arefev <arefev@xxxxxxxxx>
> > ---
> > v2: Added fixes to the srcu_schedule_cbs_snp function as suggested by
> > Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
> > kernel/rcu/srcutree.c | 4 ++--
> > 1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
> > index 20d7a238d675..6c18e6005ae1 100644
> > --- a/kernel/rcu/srcutree.c
> > +++ b/kernel/rcu/srcutree.c
> > @@ -223,7 +223,7 @@ static bool init_srcu_struct_nodes(struct srcu_struct *ssp, gfp_t gfp_flags)
> > snp->grplo = cpu;
> > snp->grphi = cpu;
> > }
> > - sdp->grpmask = 1 << (cpu - sdp->mynode->grplo);
> > + sdp->grpmask = 1UL << (cpu - sdp->mynode->grplo);
> > }
> > smp_store_release(&ssp->srcu_sup->srcu_size_state, SRCU_SIZE_WAIT_BARRIER);
> > return true;
> > @@ -833,7 +833,7 @@ static void srcu_schedule_cbs_snp(struct srcu_struct *ssp, struct srcu_node *snp
> > int cpu;
> >
> > for (cpu = snp->grplo; cpu <= snp->grphi; cpu++) {
> > - if (!(mask & (1 << (cpu - snp->grplo))))
> > + if (!(mask & (1UL << (cpu - snp->grplo))))
> > continue;
> > srcu_schedule_cbs_sdp(per_cpu_ptr(ssp->sda, cpu), delay);
> > }
>
> --
> Mathieu Desnoyers
> EfficiOS Inc.
> https://www.efficios.com
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