linux-kernel - Re: [Patch v2 4/4] x86/speculation: Add prctl to control indirect branch speculation per process

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Date:   Tue, 2 Oct 2018 11:35:30 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Tim Chen <tim.c.chen@...ux.intel.com>
Cc:     Jiri Kosina <jikos@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        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 4/4] x86/speculation: Add prctl to control indirect
 branch speculation per process


* Tim Chen <tim.c.chen@...ux.intel.com> wrote:

> To migitgate possible app to app attack from branch target buffer poisoning,
> a new prctl is provided to control branch speculation for applications in
> user app.  The following interfaces are provided:

s/migitgate
 /mitigate

> 
> prctl(PR_SET_SPECULATION_CTRL, PR_INDIR_BRANCH, PR_SPEC_DISABLE, 0, 0);
> - Disable branch target speculation to protect against app to app
> style attack using IBPB and STIBP
> 
> prctl(PR_SET_SPECULATION_CTRL, PR_INDIR_BRANCH, PR_SPEC_ENABLE, 0, 0);
> - Allow branch target speculation, no mitigation for Spectre V2
> 
> prctl(PR_GET_SPECULATION_CTRL, PR_INDIR_BRANCH, 0, 0, 0)
> - Query the indirect branch speculation restriction on a process

Well 'a process' is always 'the current process' in this case, right?

> -			lite   - only turn on mitigation for non-dumpable processes
> +			lite   - turn on mitigation for non-dumpable processes
> +				 or processes that has indirect branch restricted
> +				 via prctl's PR_SET_SPECULATION_CTRL option

s/or processes that has indirect
 /or processes that have been indirect

?

> +	/*
> +	 * If being set on non-current task, delay setting the CPU
> +	 * mitigation until it is next scheduled.
> +	 * Use speculative_store_bypass_update will update SPEC_CTRL MSR
> +	 */
> +	if (task == current && update)
> +		speculative_store_bypass_update_current();

Did you mean:

	Call to speculative_store_bypass_update_current() will update SPEC_CTRL MSR

?


> -	 * For lite protection mode, we only protect the non-dumpable
> -	 * processes.
> +	 * For lite protection mode, we protect processes  
> +	 * where the user explicitly disable indirect branch
> +	 * speculation or mark the process as non-dumpable. 

s/where the user explicitly disable
 /where the user explicitly disables

?

Thanks,

	Ingo