Messages in this thread | | | Date | Thu, 18 Apr 2024 11:50:52 +0100 | From | Sudeep Holla <> | Subject | Re: [PATCH v5 2/5] arm64: amu: Rule out potential use after free |
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On Wed, Apr 17, 2024 at 10:38:45AM +0100, Beata Michalska wrote: > For the time being, the amu_fie_cpus cpumask is being exclusively used > by the AMU-related internals of FIE support and is guaranteed to be > valid on every access currently made. Still the mask is not being > invalidated on one of the error handling code paths, which leaves > a soft spot with potential risk of uaf for CPUMASK_OFFSTACK cases. > To make things sound, set the cpumaks pointer explicitly to NULL upon > failing to register the cpufreq notifier. > Note that, due to the quirks of CPUMASK_OFFSTACK, this change needs to > be wrapped with grim ifdefing (it would be better served by > incorporating this into free_cpumask_var ...) >
Yes it doesn't look neat.
> Signed-off-by: Beata Michalska <beata.michalska@arm.com> > --- > arch/arm64/kernel/topology.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c > index 1a2c72f3e7f8..3c814a278534 100644 > --- a/arch/arm64/kernel/topology.c > +++ b/arch/arm64/kernel/topology.c > @@ -244,8 +244,12 @@ static int __init init_amu_fie(void) > > ret = cpufreq_register_notifier(&init_amu_fie_notifier, > CPUFREQ_POLICY_NOTIFIER); > - if (ret) > + if (ret) { > free_cpumask_var(amu_fie_cpus); > +#ifdef CONFIG_CPUMASK_OFFSTACK > + amu_fie_cpus = NULL; > +#endif > + }
Instead of this #ifdeffery, I was wondering if we can actually do the allocation in init_amu_fie_callback() the first time it gets called checking if amu_fie_cpus is NULL. init_amu_fie_callback() must get called only if the cpufreq_register_notifier() succeeds right ?
Also I don't see anyone calling amu_fie_setup(), so where do you think the possible use after free could occur for amu_fie_cpus. Just thinking out loud to check if I missed anything.
-- Regards, Sudeep
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