linux-kernel - Re: [PATCH] x86/cpu: Avoid endless loop to get the number of cache leaves

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Sat, 8 Dec 2018 10:46:54 +0800
From:   Pu Wen <puwen@...on.cn>
To:     <bp@...en8.de>
CC:     <tglx@...utronix.de>, <mingo@...hat.com>, <hpa@...or.com>,
        <x86@...nel.org>, <linux-kernel@...r.kernel.org>,
        Pu Wen <puwen@...on.cn>
Subject: Re: [PATCH] x86/cpu: Avoid endless loop to get the number of cache leaves

Sorry for the late reply :)

On 2018/11/16 1:22, Borislav Petkov wrote:
>> @@ -640,7 +641,7 @@ static int find_num_cache_leaves(struct cpuinfo_x86 *c)
>>   		/* Do cpuid(op) loop to find out num_cache_leaves */
>>   		cpuid_count(op, i, &eax, &ebx, &ecx, &edx);
>>   		cache_eax.full = eax;
>> -	} while (cache_eax.split.type != CTYPE_NULL);
>> +	} while (cache_eax.split.type != CTYPE_NULL && i != CTYPE_MAX);
> i is an int and CTYPE_MAX is enum _cache_type. Huh?

How about define CTYPE_MAX like this:
#define CTYPE_MAX  4

> This works by chance because CTYPE_MAX is 4 and the termination CPUID
> leaf is the 4th too.

It will return CTYPE_NULL when accessing the 4th CPUID leaf in most of
the cases, but in certain case it will not. So I think it's better to
restrict the maximum CPUID access times to 4 for kernel robustness.

-- 
Regards,
Pu Wen