linux-kernel - Re: [tip:x86/cpu] x86/cpu: Strip any /proc/ cpuinfo model name field whitespace

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Message-ID: <5566FB97.5020904@redhat.com>
Date:	Thu, 28 May 2015 07:27:19 -0400
From:	Prarit Bhargava <prarit@...hat.com>
To:	Joe Perches <joe@...ches.com>
CC:	Borislav Petkov <bp@...en8.de>, luto@...capital.net,
	peterz@...radead.org, dvlasenk@...hat.com,
	torvalds@...ux-foundation.org, imammedo@...hat.com,
	brgerst@...il.com, mingo@...nel.org, dave.hansen@...ux.intel.com,
	fenghua.yu@...el.com, hpa@...or.com, linux-kernel@...r.kernel.org,
	tglx@...utronix.de, bp@...e.de, linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/cpu] x86/cpu: Strip any /proc/ cpuinfo model name field
 whitespace

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
> 
> 
> 

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