[PATCH 2/2] arch_topology: Sanity check cpumask in thermal pressure update

[Bjorn Andersson]

Occasionally during boot the Qualcomm cpufreq driver was able to cause
an invalid memory access in topology_update_thermal_pressure() on the
line:

	if (max_freq <= capped_freq)

It turns out that this was caused by a race, which resulted in the
cpumask passed to the function being empty, in which case
cpumask_first() will return a cpu beyond the number of valid cpus, which
when used to access the per_cpu max_freq would return invalid pointer.

The bug in the Qualcomm cpufreq driver is being fixed, but having a
sanity check of the arguments would have saved quite a bit of time and
it's not unlikely that others will run into the same issue.

Signed-off-by: Bjorn Andersson <bjorn.andersson@xxxxxxxxxx>
---
 drivers/base/arch_topology.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
index 976154140f0b..6560a0c3b969 100644
--- a/drivers/base/arch_topology.c
+++ b/drivers/base/arch_topology.c
@@ -177,6 +177,9 @@ void topology_update_thermal_pressure(const struct cpumask *cpus,
 	u32 max_freq;
 	int cpu;
 
+	if (WARN_ON(cpumask_empty(cpus)))
+		return;
+
 	cpu = cpumask_first(cpus);
 	max_capacity = arch_scale_cpu_capacity(cpu);
 	max_freq = per_cpu(freq_factor, cpu);
-- 
2.33.1