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Re: [PATCH] x86/pmstat: Check size of PMSTAT_get_pxstat buffers


  • To: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
  • From: Jan Beulich <jbeulich@xxxxxxxx>
  • Date: Thu, 17 Apr 2025 15:23:18 +0200
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  • Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx
  • Delivery-date: Thu, 17 Apr 2025 13:23:30 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 17.04.2025 12:30, Ross Lagerwall wrote:
> --- a/xen/drivers/acpi/pmstat.c
> +++ b/xen/drivers/acpi/pmstat.c
> @@ -104,6 +104,14 @@ int do_get_pm_info(struct xen_sysctl_get_pmstat *op)
>          cpufreq_residency_update(op->cpuid, pxpt->u.cur);
>  
>          ct = pmpt->perf.state_count;
> +
> +        if ( op->u.getpx.total < ct )
> +        {
> +            spin_unlock(cpufreq_statistic_lock);
> +            ret = -ENOSPC;
> +            break;
> +        }

Simply producing an error is not an option imo. See pmstat_get_cx_stat()'s
behavior. Imo the calculation of ct wants to become

        ct = min(pmpt->perf.state_count, op->u.getpx.total);

yet then the copying of the 2-dim array of data becomes more complicated
when ct < pmpt->perf.state_count. An option may be to document that this
array is copied only when the buffer is large enough.

Furthermore I think it would be a good idea to also amend the public header
with IN/OUT annotations for the fields which are input and output (also for
the Cx part, ideally).

And then - doesn't xc_pm_get_pxstat() have a similar issue?

Jan



 


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