linux-kernel - Re: [Patch v2 2/4] x86/speculation: Provide application property based STIBP protection

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Date:   Thu, 4 Oct 2018 12:19:46 -0700
From:   Tim Chen <tim.c.chen@...ux.intel.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Jiri Kosina <jikos@...nel.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Andi Kleen <ak@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Casey Schaufler <casey.schaufler@...el.com>,
        Asit Mallick <asit.k.mallick@...el.com>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        Jon Masters <jcm@...hat.com>, linux-kernel@...r.kernel.org,
        x86@...nel.org
Subject: Re: [Patch v2 2/4] x86/speculation: Provide application property
 based STIBP protection

On 10/02/2018 12:10 PM, Thomas Gleixner wrote:
> On Tue, 25 Sep 2018, Tim Chen wrote:
> 
>> This patch provides an application property based spectre_v2
> 
> # git grep 'This patch' Documentation/process/
> 
>> protection with STIBP against attack from another app from
> 
> s/app/application/ please. This is not android.
> 
>> a sibling hyper-thread.  For security sensitive non-dumpable
>> app, STIBP will be turned on before switching to it for Intel
>> processors vulnerable to spectre_v2.
> 
> What has this to do with Intel processors?
> 
>> -static __always_inline void intel_set_ssb_state(unsigned long tifn)
>> +static __always_inline void set_spec_ctrl_state(unsigned long tifn)
>>  {
>> -	u64 msr = x86_spec_ctrl_base | ssbd_tif_to_spec_ctrl(tifn);
>> +	u64 msr = x86_spec_ctrl_base;
>> +
>> +	if (static_cpu_has(X86_FEATURE_SSBD))
>> +		msr |= ssbd_tif_to_spec_ctrl(tifn);
>> +
>> +	if (cpu_smt_control == CPU_SMT_ENABLED)
>> +		msr |= stibp_tif_to_spec_ctrl(tifn);
> 
> Oh no. We are not adding yet another conditional into switch to. Either
> that's done unconditionally or this wants to have a static key.

Okay, will add a static_key to indicate that SMT is in use.

Tim

> 
>>  	wrmsrl(MSR_IA32_SPEC_CTRL, msr);
> 
> Thanks,
> 
> 	tglx
>