Re: [Xen-devel] [PATCH 2/2] x86/cpufreq: Avoid using processor_pminfo[cpu] when it is NULL

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 12.08.16 at 12:35, <andrew.cooper3@xxxxxxxxxx> wrote:
> The undefined behaviour sanitiser shows that it really is NULL via the
> pre_initcall path.
> 
>   (XEN) 
> ================================================================================
>   (XEN) UBSAN: Undefined behaviour in cpufreq.c:158:66
>   (XEN) member access within null pointer of type 'struct processor_pminfo'
>   (XEN) ----[ Xen-4.8-unstable  x86_64  debug=y  Not tainted ]----
>   <snip>
>   (XEN)    [<ffff82d0801c4231>] cpufreq_add_cpu+0x161/0xdc0
>   (XEN)    [<ffff82d0801c6610>] cpufreq.c#cpu_callback+0x20/0x30
>   (XEN)    [<ffff82d0804eefad>] cpufreq.c#cpufreq_presmp_init+0x2d/0x50
>   (XEN)    [<ffff82d0804c5942>] do_presmp_initcalls+0x22/0x30
>   (XEN)    [<ffff82d08051852d>] __start_xen+0x378d/0x42f0
>   (XEN)    [<ffff82d080100073>] __high_start+0x53/0x60
> 
> Fix two other occurances of the same buggy logic.
> 
> The processor_pminfo[] objects are only allocated as a result of
> XENPF_set_processor_pminfo hypercalls, which means that this early cpu
> callback will always hit the early NULL check, and is therefore pointless.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>


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