Re: [PATCH v9 3/5] arm64: amu: Delay allocating cpumask for AMU FIE support

Sumit Gupta
2025-01-29T11:18:01Z

On 21/01/25 14:14, 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 theoretical risk of UAF for CPUMASK_OFFSTACK cases.
> To make things sound, delay allocating said cpumask
> (for CPUMASK_OFFSTACK) avoiding otherwise nasty sanitising case failing
> to register the cpufreq policy notifications.
>
> Signed-off-by: Beata Michalska <beata.michalska@arm.com>

Reviewed-by: Sumit Gupta <sumitg@nvidia.com>

> ---
> arch/arm64/kernel/topology.c | 22 ++++++++++------------
> 1 file changed, 10 insertions(+), 12 deletions(-)
>
> diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
> index 1a2c72f3e7f8..cb180684d10d 100644
> --- a/arch/arm64/kernel/topology.c
> +++ b/arch/arm64/kernel/topology.c
> @@ -194,12 +194,19 @@ static void amu_fie_setup(const struct cpumask *cpus)
> int cpu;
>
> /* We are already set since the last insmod of cpufreq driver */
> - if (unlikely(cpumask_subset(cpus, amu_fie_cpus)))
> + if (cpumask_available(amu_fie_cpus) &&
> + unlikely(cpumask_subset(cpus, amu_fie_cpus)))
> return;
>
> - for_each_cpu(cpu, cpus) {
> + for_each_cpu(cpu, cpus)
> if (!freq_counters_valid(cpu))
> return;
> +
> + if (!cpumask_available(amu_fie_cpus) &&
> + !zalloc_cpumask_var(&amu_fie_cpus, GFP_KERNEL)) {
> + WARN_ONCE(1, "Failed to allocate FIE cpumask for CPUs[%*pbl]\n",
> + cpumask_pr_args(cpus));
> + return;
> }
>
> cpumask_or(amu_fie_cpus, amu_fie_cpus, cpus);
> @@ -237,17 +244,8 @@ static struct notifier_block init_amu_fie_notifier = {
>
> static int __init init_amu_fie(void)
> {
> - int ret;
> -
> - if (!zalloc_cpumask_var(&amu_fie_cpus, GFP_KERNEL))
> - return -ENOMEM;
> -
> - ret = cpufreq_register_notifier(&init_amu_fie_notifier,
> + return cpufreq_register_notifier(&init_amu_fie_notifier,
> CPUFREQ_POLICY_NOTIFIER);
> - if (ret)
> - free_cpumask_var(amu_fie_cpus);
> -
> - return ret;
> }
> core_initcall(init_amu_fie);
>
> --
> 2.25.1
>