arm64: amu: Delay allocating cpumask for AMU FIE support

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: Prasanna Kumar T S M <ptsm@linux.microsoft.com>
Reviewed-by: Sumit Gupta <sumitg@nvidia.com>
Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>
Link: https://lore.kernel.org/r/20250131155842.3839098-1-beata.michalska@arm.com
Signed-off-by: Will Deacon <will@kernel.org>

diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
index 1a2c72f3e7f80ed298b1a4a9b6c395febd1d626d..cb180684d10d5b5be90602878ce75f44da90d696 100644 (file)
--- 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);