linux-kernel - Re: [PATCH v11 06/20] x86/sev: Handle failures from snp

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Message-ID: <20240828094933.GAZs7yrbCHDJUeUWys@fat_crate.local>
Date: Wed, 28 Aug 2024 11:49:33 +0200
From: Borislav Petkov <bp@...en8.de>
To: "Nikunj A. Dadhania" <nikunj@....com>
Cc: linux-kernel@...r.kernel.org, thomas.lendacky@....com, x86@...nel.org,
	kvm@...r.kernel.org, mingo@...hat.com, tglx@...utronix.de,
	dave.hansen@...ux.intel.com, pgonda@...gle.com, seanjc@...gle.com,
	pbonzini@...hat.com
Subject: Re: [PATCH v11 06/20] x86/sev: Handle failures from snp_init()

On Wed, Aug 28, 2024 at 10:17:57AM +0530, Nikunj A. Dadhania wrote:
> +	if ((snp && !snp_enabled) ||
> +	    (!snp && snp_enabled))
>  		snp_abort();

And which boolean function is that?

diff --git a/arch/x86/mm/mem_encrypt_identity.c b/arch/x86/mm/mem_encrypt_identity.c
index e83b363c5e68..706cb59851b0 100644
--- a/arch/x86/mm/mem_encrypt_identity.c
+++ b/arch/x86/mm/mem_encrypt_identity.c
@@ -495,10 +495,10 @@ void __head sme_enable(struct boot_params *bp)
 	unsigned int eax, ebx, ecx, edx;
 	unsigned long feature_mask;
 	unsigned long me_mask;
-	bool snp;
+	bool snp_en;
 	u64 msr;
 
-	snp = snp_init(bp);
+	snp_en = snp_init(bp);
 
 	/* Check for the SME/SEV support leaf */
 	eax = 0x80000000;
@@ -531,15 +531,11 @@ void __head sme_enable(struct boot_params *bp)
 	RIP_REL_REF(sev_status) = msr = __rdmsr(MSR_AMD64_SEV);
 	feature_mask = (msr & MSR_AMD64_SEV_ENABLED) ? AMD_SEV_BIT : AMD_SME_BIT;
 
-	/* The SEV-SNP CC blob should never be present unless SEV-SNP is enabled. */
-	if (snp && !(msr & MSR_AMD64_SEV_SNP_ENABLED))
-		snp_abort();
-
 	/*
-	 * The SEV-SNP CC blob should be present and parsing CC blob should
-	 * succeed when SEV-SNP is enabled.
+	 * Any discrepancies between the presence of a CC blob and SNP
+	 * enablement abort the guest.
 	 */
-	if (!snp && (msr & MSR_AMD64_SEV_SNP_ENABLED))
+	if (snp_en ^ (msr & MSR_AMD64_SEV_SNP_ENABLED))
 		snp_abort();
 
 	/* Check if memory encryption is enabled */

-- 
Regards/Gruss,
    Boris.

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