linux-kernel - Re: [PATCH v9 10/14] x86/cpu/keylocker: Check Gather Data Sampling mitigation

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Date: Thu, 28 Mar 2024 23:57:42 -0700
From: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
To: "Chang S. Bae" <chang.seok.bae@...el.com>
Cc: linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org,
	dm-devel@...hat.com, ebiggers@...nel.org, luto@...nel.org,
	dave.hansen@...ux.intel.com, tglx@...utronix.de, bp@...en8.de,
	mingo@...nel.org, x86@...nel.org, herbert@...dor.apana.org.au,
	ardb@...nel.org, elliott@....com, dan.j.williams@...el.com,
	bernie.keany@...el.com, charishma1.gairuboyina@...el.com,
	Dave Hansen <dave.hansen@...el.com>
Subject: Re: [PATCH v9 10/14] x86/cpu/keylocker: Check Gather Data Sampling
 mitigation

On Thu, Mar 28, 2024 at 06:53:42PM -0700, Chang S. Bae wrote:
> +/*
> + * The mitigation is implemented at a microcode level. Ensure that the
> + * microcode update is applied and the mitigation is locked.
> + */
> +static bool __init have_gds_mitigation(void)
> +{
> +	u64 mcu_ctrl;
> +
> +	/* GDS_CTRL is set if new microcode is loaded. */
> +	if (!(x86_read_arch_cap_msr() & ARCH_CAP_GDS_CTRL))
> +		goto vulnerable;
> +
> +	/* If GDS_MITG_LOCKED is set, GDS_MITG_DIS is forced to 0. */
> +	rdmsrl(MSR_IA32_MCU_OPT_CTRL, mcu_ctrl);
> +	if (mcu_ctrl & GDS_MITG_LOCKED)
> +		return true;

Similar to RFDS, above checks can be simplified to:

	if (gds_mitigation == GDS_MITIGATION_FULL_LOCKED)
		return true;
> +
> +vulnerable:
> +	pr_warn("x86/keylocker: Susceptible to the GDS vulnerability.\n");
> +	return false;
> +}