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

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Tue, Jan 18, 2022 at 10:56:12AM -0800, Bjorn Andersson wrote:
> 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@linaro.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;

Sorry, but I do not want to add any more WARN_ON() calls to the kernel
unless really needed.  We don't try to save the kernel from itself all
the time by validating every internal api call parameters.

thjanks,

greg k-h