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Date: Thu, 28 May 2015 07:27:19 -0400
From: Prarit Bhargava <prarit@redhat.com>
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To: Joe Perches <joe@perches.com>
CC: Borislav Petkov <bp@alien8.de>, luto@amacapital.net, peterz@infradead.org,
        dvlasenk@redhat.com, torvalds@linux-foundation.org,
        imammedo@redhat.com, brgerst@gmail.com, mingo@kernel.org,
        dave.hansen@linux.intel.com, fenghua.yu@intel.com, hpa@zytor.com,
        linux-kernel@vger.kernel.org, tglx@linutronix.de, bp@suse.de,
        linux-tip-commits@vger.kernel.org
Subject: Re: [tip:x86/cpu] x86/cpu: Strip any /proc/ cpuinfo model name field
 whitespace
References: <1432050210-32036-1-git-send-email-prarit@redhat.com>  <1432628901-18044-15-git-send-email-bp@alien8.de>  <tip-adafb98da6a7af5e45362933a7dae6ab0e5076bf@git.kernel.org>  <1432746454.2846.154.camel@perches.com> <20150527190626.GC19407@pd.tnic> <1432754207.2846.162.camel@perches.com>
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On 05/27/2015 03:16 PM, Joe Perches wrote:
> On Wed, 2015-05-27 at 21:06 +0200, Borislav Petkov wrote:
>> On Wed, May 27, 2015 at 10:07:34AM -0700, Joe Perches wrote:
>>> This code can memmove from beyond the x86_model_id field.
>>
>> ... in the theoretical case where some model ID has more than 64 - 48
>> preceding white spaces.
>>
>> I guess we want to be prepared here for insane CPU model IDs coming from
>> virtualization.
>>
>>> Maybe:
>>> 	char *model = strim(c->x86_model_id);
>>> 	memmove(c->x86_model_id, model, strlen(model) + 1);
>>
>> Yes, and additionally limit that string length:
>>
>> ---
>> diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
> []
>> @@ -383,6 +383,9 @@ static const struct cpu_dev *cpu_devs[X86_VENDOR_NUM] = {};
>>  static void get_model_name(struct cpuinfo_x86 *c)
>>  {
>>  	unsigned int *v;
>> +	const char *model;
>> +
>> +#define MODEL_ID_MAXLEN 48
>>  
>>  	if (c->extended_cpuid_level < 0x80000004)
>>  		return;
>> @@ -391,13 +394,15 @@ static void get_model_name(struct cpuinfo_x86 *c)
>>  	cpuid(0x80000002, &v[0], &v[1], &v[2], &v[3]);
>>  	cpuid(0x80000003, &v[4], &v[5], &v[6], &v[7]);
>>  	cpuid(0x80000004, &v[8], &v[9], &v[10], &v[11]);
>> -	c->x86_model_id[48] = 0;
>> +	c->x86_model_id[MODEL_ID_MAXLEN] = 0;
>>  
>>  	/*
>>  	 * Remove leading whitespace on Intel processors and trailing
>>  	 * whitespace on AMD processors.
>>  	 */
>> -	memmove(c->x86_model_id, strim(c->x86_model_id), 48);
>> +	model = strim(c->x86_model_id);
>> +
>> +	memmove(c->x86_model_id, model, strnlen(model, MODEL_ID_MAXLEN) + 1);
> 
> I don't see any value in the #define or strnlen over strlen as
> it's guaranteed terminated by the = 0 above, but <shrug> thanks.
> 

FWIW, I agree with Joe here and don't think the #define is necessary.
I will post a follow-up patch against tip on LKML shortly.

P.

> cheers, Joe
> 
> 
>