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

[Sumit Gupta <sumitg@nvidia.com>]

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
>