linux-kernel - Re: [PATCH v5 09/16] x86/bugs: add lfence mitigation to spectre v2 and no meltdown for Hygon

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Date:   Wed, 5 Sep 2018 18:40:09 +0800
From:   Pu Wen <puwen@...on.cn>
To:     Borislav Petkov <bp@...en8.de>
Cc:     tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
        x86@...nel.org, thomas.lendacky@....com, pbonzini@...hat.com,
        linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org
Subject: Re: [PATCH v5 09/16] x86/bugs: add lfence mitigation to spectre v2
 and no meltdown for Hygon

On 2018/9/5 17:13, Borislav Petkov wrote:
>>   static const char *spectre_v2_strings[] = {
>>   	[SPECTRE_V2_NONE]			= "Vulnerable",
>>   	[SPECTRE_V2_RETPOLINE_MINIMAL]		= "Vulnerable: Minimal generic ASM retpoline",
>> -	[SPECTRE_V2_RETPOLINE_MINIMAL_AMD]	= "Vulnerable: Minimal AMD ASM retpoline",
>> +	[SPECTRE_V2_RETPOLINE_MINIMAL_LFENCE]	= "Vulnerable: Minimal LFENCE ASM retpoline",
>>   	[SPECTRE_V2_RETPOLINE_GENERIC]		= "Mitigation: Full generic retpoline",
>> -	[SPECTRE_V2_RETPOLINE_AMD]		= "Mitigation: Full AMD retpoline",
>> +	[SPECTRE_V2_RETPOLINE_LFENCE]		= "Mitigation: Full LFENCE retpoline",
>>   	[SPECTRE_V2_IBRS_ENHANCED]		= "Mitigation: Enhanced IBRS",
>>   };
> 
> This is user-visible and with all the back'n'forth and backporting
> and the whole security fiasco, I don't want to have another source of
> confusion. You'll have to live with it saying "AMD" in dmesg
....
>> @@ -272,7 +272,7 @@ static const struct {
>>   	{ "off",               SPECTRE_V2_CMD_NONE,              false },
>>   	{ "on",                SPECTRE_V2_CMD_FORCE,             true },
>>   	{ "retpoline",         SPECTRE_V2_CMD_RETPOLINE,         false },
>> -	{ "retpoline,amd",     SPECTRE_V2_CMD_RETPOLINE_AMD,     false },
>> +	{ "retpoline,lfence",     SPECTRE_V2_CMD_RETPOLINE_LFENCE,     false },
>>   	{ "retpoline,generic", SPECTRE_V2_CMD_RETPOLINE_GENERIC, false },
>>   	{ "auto",              SPECTRE_V2_CMD_AUTO,              false },
>>   };
> 
> This even more so. Those are command line strings which we're still
> communicating to people, even. So no, it needs to remain "retpoline,amd"
> on Hygon.
> 
> And then to not confuse people staring at the code either, we can drop
> this change too:
> 
> -     SPECTRE_V2_CMD_RETPOLINE_AMD,
> +     SPECTRE_V2_CMD_RETPOLINE_LFENCE,
> 
> Which leaves this patch only with the addition of the vendor tests. The
> other stuff you can drop.

That's reasonable. To avoid the confusion, will only leave the vendor
testing for Hygon and drop the other changes, which also minimize the
code modification.

-- 
Regards,
Pu Wen