linux-kernel - Re: [Patch v5 11/16] x86/speculation: Add Spectre v2 app to app protection modes

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Message-ID: <alpine.DEB.2.21.1811192133240.1669@nanos.tec.linutronix.de>
Date:   Mon, 19 Nov 2018 21:46:44 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Tim Chen <tim.c.chen@...ux.intel.com>
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>,
        Waiman Long <longman9394@...il.com>,
        linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [Patch v5 11/16] x86/speculation: Add Spectre v2 app to app
 protection modes

On Fri, 16 Nov 2018, Tim Chen wrote:
> +static const struct {
> +	const char *option;
> +	enum spectre_v2_app2app_mitigation_cmd cmd;
> +	bool secure;
> +} app2app_options[] = {
> +	{ "off",	SPECTRE_V2_APP2APP_CMD_NONE,   false },
> +	{ "lite",	SPECTRE_V2_APP2APP_CMD_LITE,   false },
> +	{ "strict",	SPECTRE_V2_APP2APP_CMD_STRICT, false },
> +	{ "auto",	SPECTRE_V2_APP2APP_CMD_AUTO,   false },
> +	/*
> +	 * The "on" option is kept as last entry. It is implied by
> +	 * spectre_v2=on boot parameter and it is not checked
> +	 * in spectre_v2_app2app boot parameter.
> +	 */
> +	{ "on",		SPECTRE_V2_APP2APP_CMD_FORCE,  true  },

FORCE is the same as STRICT. What's the point?

> @@ -376,6 +464,8 @@ static void __init spectre_v2_select_mitigation(void)
>  {
>  	enum spectre_v2_mitigation_cmd cmd = spectre_v2_parse_cmdline();
>  	enum spectre_v2_mitigation mode = SPECTRE_V2_NONE;
> +	enum spectre_v2_app2app_mitigation_cmd app2app_cmd;
> +	enum spectre_v2_app2app_mitigation app2app_mode;
>  
>  	/*
>  	 * If the CPU is not affected and the command line mode is NONE or AUTO
> @@ -452,12 +542,6 @@ static void __init spectre_v2_select_mitigation(void)
>  	setup_force_cpu_cap(X86_FEATURE_RSB_CTXSW);
>  	pr_info("Spectre v2 / SpectreRSB mitigation: Filling RSB on context switch\n");
>  
> -	/* Initialize Indirect Branch Prediction Barrier if supported */
> -	if (boot_cpu_has(X86_FEATURE_IBPB)) {
> -		setup_force_cpu_cap(X86_FEATURE_USE_IBPB);
> -		pr_info("Spectre v2 mitigation: Enabling Indirect Branch Prediction Barrier\n");
> -	}
> -
>  	/*
>  	 * Retpoline means the kernel is safe because it has no indirect
>  	 * branches. Enhanced IBRS protects firmware too, so, enable restricted
> @@ -474,6 +558,43 @@ static void __init spectre_v2_select_mitigation(void)
>  		pr_info("Enabling Restricted Speculation for firmware calls\n");
>  	}
>  
> +	app2app_mode = SPECTRE_V2_APP2APP_NONE;
> +	if (!boot_cpu_has(X86_FEATURE_IBPB) ||
> +	    !boot_cpu_has(X86_FEATURE_STIBP))
> +		goto set_app2app_mode;

So before that change IBPB was usable without STIBP, now not longer. What's
the rationale?

This patch changes a gazillion things at once and is completely
unreviewable.

Thanks,

	tglx