linux-kernel - Re: [PATCH v12 02/19] x86/sev: Handle failures from snp

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Message-ID: <03840d96-8fd4-b0c1-f6da-f69ed25cb4f0@amd.com>
Date: Wed, 16 Oct 2024 11:16:45 -0500
From: Tom Lendacky <thomas.lendacky@....com>
To: Nikunj A Dadhania <nikunj@....com>, linux-kernel@...r.kernel.org,
 bp@...en8.de, x86@...nel.org, kvm@...r.kernel.org
Cc: mingo@...hat.com, tglx@...utronix.de, dave.hansen@...ux.intel.com,
 pgonda@...gle.com, seanjc@...gle.com, pbonzini@...hat.com
Subject: Re: [PATCH v12 02/19] x86/sev: Handle failures from snp_init()

On 10/9/24 04:28, Nikunj A Dadhania wrote:
> Address the ignored failures from snp_init() in sme_enable(). Add error
> handling for scenarios where snp_init() fails to retrieve the SEV-SNP CC
> blob or encounters issues while parsing the CC blob. Ensure that SNP guests
> will error out early, preventing delayed error reporting or undefined
> behavior.
> 
> Signed-off-by: Nikunj A Dadhania <nikunj@....com>

Reviewed-by: Tom Lendacky <thomas.lendacky@....com>

> ---
>  arch/x86/mm/mem_encrypt_identity.c | 11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/mm/mem_encrypt_identity.c b/arch/x86/mm/mem_encrypt_identity.c
> index ac33b2263a43..e6c7686f443a 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;
> @@ -531,8 +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))
> +	/*
> +	 * Any discrepancies between the presence of a CC blob and SNP
> +	 * enablement abort the guest.
> +	 */
> +	if (snp_en ^ !!(msr & MSR_AMD64_SEV_SNP_ENABLED))
>  		snp_abort();
>  
>  	/* Check if memory encryption is enabled */