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

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Message-Id: <20220118185612.2067031-2-bjorn.andersson@linaro.org>
Date:   Tue, 18 Jan 2022 10:56:12 -0800
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Sudeep Holla <sudeep.holla@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Lukasz Luba <lukasz.luba@....com>,
        Vladimir Zapolskiy <vladimir.zapolskiy@...aro.org>
Cc:     Thara Gopinath <thara.gopinath@...il.com>,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-pm@...r.kernel.org
Subject: [PATCH 2/2] arch_topology: Sanity check cpumask in thermal pressure update

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@...aro.org>
---
 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