linux-kernel - Re: [PATCH] x86, cpuinfo x86_model

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Date:	Tue, 19 May 2015 13:25:59 -0400
From:	Brian Gerst <brgerst@...il.com>
To:	Prarit Bhargava <prarit@...hat.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"the arch/x86 maintainers" <x86@...nel.org>,
	Andy Lutomirski <luto@...capital.net>,
	Borislav Petkov <bp@...en8.de>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Igor Mammedov <imammedo@...hat.com>,
	Fenghua Yu <fenghua.yu@...el.com>
Subject: Re: [PATCH] x86, cpuinfo x86_model_id whitespace cleanup

On Tue, May 19, 2015 at 11:43 AM, Prarit Bhargava <prarit@...hat.com> 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
> quick investigation it was noticed that the model name fields were actually
> different -- processor 0's model name field had trailing 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@...rit ~]# 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
> to output a pretty message to the console in print_cpu_info(), and as a
> result truncates the whitespace at the end of the x86_model_id field.
>
> The x86_model_id field should be the same for the same processors.  This
> patch uses string functions to remove both leading and trailing whitespace
> in the x86_model_id field.  As a result the print_cpu_info() output looks
> like
>
> smpboot: CPU0: AMD Opteron(TM) Processor 6272 (fam: 15, model: 01, stepping: 02)
>
> and the x86_model_id field is correct on all processors on AMD platforms
>
> [thetango@...rit ~]# grep "^model name" /proc/cpuinfo | uniq -c | sed 's/\ /_/g'
> _____64_model_name      :_AMD_Opteron(TM)_Processor_6272
>
> and the functionality is correct on an Intel box:
>
> [thetango@...rit2]# grep "^model name" /proc/cpuinfo | uniq -c | sed 's/\ /_/g'
> ____144_model_name      :_Intel(R)_Xeon(R)_CPU_E7-8890_v3_@...50GHz
>
> Signed-off-by: Prarit Bhargava <prarit@...hat.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Cc: x86@...nel.org
> Cc: Andy Lutomirski <luto@...capital.net>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: Denys Vlasenko <dvlasenk@...hat.com>
> Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> Cc: Igor Mammedov <imammedo@...hat.com>
> Cc: Fenghua Yu <fenghua.yu@...el.com>
> Cc: Brian Gerst <brgerst@...il.com>
> ---
>  arch/x86/kernel/cpu/common.c |   17 ++++-------------
>  1 file changed, 4 insertions(+), 13 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
> index a62cf04..9405c1e 100644
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c
> @@ -419,7 +419,6 @@ static const struct cpu_dev *cpu_devs[X86_VENDOR_NUM] = {};
>  static void get_model_name(struct cpuinfo_x86 *c)
>  {
>         unsigned int *v;
> -       char *p, *q;
>
>         if (c->extended_cpuid_level < 0x80000004)
>                 return;
> @@ -431,18 +430,10 @@ static void get_model_name(struct cpuinfo_x86 *c)
>         c->x86_model_id[48] = 0;
>
>         /*
> -        * Intel chips right-justify this string for some dumb reason;
> -        * undo that brain damage:
> +        * Remove leading whitespace on Intel processors and trailing
> +        * whitespace on AMD processors.
>          */
> -       p = q = &c->x86_model_id[0];
> -       while (*p == ' ')
> -               p++;
> -       if (p != q) {
> -               while (*p)
> -                       *q++ = *p++;
> -               while (q <= &c->x86_model_id[48])
> -                       *q++ = '\0';    /* Zero-pad the rest */
> -       }
> +       strlcpy(c->x86_model_id, strim(c->x86_model_id), 48);
>  }

Using strlcpy in this manner could fail if it does larger than byte
copies and they overlap.  I would instead allocate a temp buffer on
the stack:

    unsigned char model_id[49];
    v = (unsigned int *)model_id;
   ...
    strlcpy(c->x86_model_id, strim(model_id), 48);

--
Brian Gerst
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