linux-kernel - Re: [PATCH 3/3] x86/bugs: Simplify SSB cmdline parsing

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Message-ID: <20250818174157.c6bzy5bgw54fopgi@desk>
Date: Mon, 18 Aug 2025 10:41:57 -0700
From: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
To: David Kaplan <david.kaplan@....com>
Cc: Thomas Gleixner <tglx@...utronix.de>, Borislav Petkov <bp@...en8.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Josh Poimboeuf <jpoimboe@...nel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	"H . Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] x86/bugs: Simplify SSB cmdline parsing

On Mon, Aug 11, 2025 at 09:26:59AM -0500, David Kaplan wrote:
> Simplify the SSB command line parsing by selecting a mitigation directly,
> as is done in most of the simpler vulnerabilities.  Use early_param instead
> of cmdline_find_option for consistency with the other mitigation
> selections.
> 
> Signed-off-by: David Kaplan <david.kaplan@....com>
> ---
>  arch/x86/kernel/cpu/bugs.c | 118 ++++++++++++-------------------------
>  1 file changed, 39 insertions(+), 79 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
> index 19a3891953c3..3766dff9a699 100644
> --- a/arch/x86/kernel/cpu/bugs.c
> +++ b/arch/x86/kernel/cpu/bugs.c
> @@ -2625,16 +2625,8 @@ void cpu_bugs_smt_update(void)
>  #undef pr_fmt
>  #define pr_fmt(fmt)	"Speculative Store Bypass: " fmt
>  
> -static enum ssb_mitigation ssb_mode __ro_after_init = SPEC_STORE_BYPASS_NONE;
> -
> -/* The kernel command line selection */
> -enum ssb_mitigation_cmd {
> -	SPEC_STORE_BYPASS_CMD_NONE,
> -	SPEC_STORE_BYPASS_CMD_AUTO,
> -	SPEC_STORE_BYPASS_CMD_ON,
> -	SPEC_STORE_BYPASS_CMD_PRCTL,
> -	SPEC_STORE_BYPASS_CMD_SECCOMP,
> -};
> +static enum ssb_mitigation ssb_mode __ro_after_init =
> +	IS_ENABLED(CONFIG_MITIGATION_SSB) ? SPEC_STORE_BYPASS_PRCTL : SPEC_STORE_BYPASS_NONE;

Other mitigations default to "AUTO", but not this one. Isn't that something
that attack-vector controls rely on?