Re: [PATCH] x86, cpuinfo fix cpu_data(0) x86_model_id field truncation

[Brian Gerst]

On Mon, May 18, 2015 at 3:45 PM, Borislav Petkov <bp@xxxxxxxxx> wrote:
> On Mon, May 18, 2015 at 02:21:00PM -0400, Prarit Bhargava wrote:
>> When comparing 'model name' fields in /proc/cpuinfo it was noticed that
>> a simple test comparing the model name fields was failing.  After some
>> simple investigation it was noticed that, in fact, the model name fields
>> are different for each processor.  Processor 0's model name field had
>> white space removed, while the other processors did not.
>>
>> Another way of seeing this behaviour is to convert spaces into underscores
>> in the output of /proc/cpuinfo,
>>
>> [thetango@prarit ~]# grep "^model name" /proc/cpuinfo | uniq -c | sed 's/\ /_/g'
>> ______1_model_name      :_AMD_Opteron(TM)_Processor_6272
>> _____63_model_name      :_AMD_Opteron(TM)_Processor_6272_________________
>>
>> which shows two different model name fields even though they should be the
>> same.
>>
>> This occurs because the kernel calls strim() on cpu 0's x86_model_id field
>
> I'd actually prefer this much simpler patch:
>
> ---
> diff --git a/arch/x86/kernel/cpu/proc.c b/arch/x86/kernel/cpu/proc.c
> index e7d8c7608471..d215e9b26567 100644
> --- a/arch/x86/kernel/cpu/proc.c
> +++ b/arch/x86/kernel/cpu/proc.c
> @@ -67,7 +67,7 @@ static int show_cpuinfo(struct seq_file *m, void *v)
>                    c->x86_vendor_id[0] ? c->x86_vendor_id : "unknown",
>                    c->x86,
>                    c->x86_model,
> -                  c->x86_model_id[0] ? c->x86_model_id : "unknown");
> +                  c->x86_model_id[0] ? strim(c->x86_model_id) : "unknown");
>
>         if (c->x86_mask || c->cpuid_level >= 0)
>                 seq_printf(m, "stepping\t: %d\n", c->x86_mask);

The problem here is that strim() modifies the string in place,
replacing the first trailing space with a null.  I think the best
solution is to do the trimming in get_model_name().  It already trims
leading spaces for Intel.

--
Brian Gerst
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