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

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Message-ID: <5b62f751-668f-714e-24a2-6bbc188c3ce8@amd.com>
Date: Wed, 28 Aug 2024 10:17:57 +0530
From: "Nikunj A. Dadhania" <nikunj@....com>
To: Borislav Petkov <bp@...en8.de>
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()

Hi Boris,

On 8/27/2024 5:02 PM, Borislav Petkov wrote:
> On Wed, Jul 31, 2024 at 08:37:57PM +0530, 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.
> 
> Is this a real issue you've encountered or?

As per you comment [1], you had suggested to error out early in snp_init()
instead of waiting till snp_init_platform_device(). As snp_init() was
ignoring the failure case, I have added this patch. Following patch adds
secrets page parsing from CC blob. When the parsing fails, snp_init() will
return failure.

> 
>> This change ensures
> 
> Avoid having "This patch" or "This commit" or "This <whatever>" in the commit
> message. It is tautologically useless.

Sure, will do.
 
>> diff --git a/arch/x86/mm/mem_encrypt_identity.c b/arch/x86/mm/mem_encrypt_identity.c
>> index ac33b2263a43..e83b363c5e68 100644
>> --- a/arch/x86/mm/mem_encrypt_identity.c
>> +++ b/arch/x86/mm/mem_encrypt_identity.c
>> @@ -535,6 +535,13 @@ void __head sme_enable(struct boot_params *bp)
>>  	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.
>> +	 */
>> +	if (!snp && (msr & MSR_AMD64_SEV_SNP_ENABLED))
>> +		snp_abort();
> 
> Any chance you could combine the above and this test?
> 
> Perhaps look around at the code before adding your check - there might be some
> opportunity for aggregation and improvement...

Sure, how about the below patch ?

From: Nikunj A Dadhania <nikunj@....com>
Date: Wed, 22 May 2024 12:43:42 +0530
Subject: [PATCH] x86/sev: Handle failures from snp_init()

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>
---
 arch/x86/mm/mem_encrypt_identity.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/arch/x86/mm/mem_encrypt_identity.c b/arch/x86/mm/mem_encrypt_identity.c
index ac33b2263a43..a0124a479972 100644
--- a/arch/x86/mm/mem_encrypt_identity.c
+++ b/arch/x86/mm/mem_encrypt_identity.c
@@ -495,7 +495,7 @@ 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, snp_enabled;
 	u64 msr;
 
 	snp = snp_init(bp);
@@ -529,10 +529,17 @@ void __head sme_enable(struct boot_params *bp)
 
 	/* Check the SEV MSR whether SEV or SME is enabled */
 	RIP_REL_REF(sev_status) = msr = __rdmsr(MSR_AMD64_SEV);
-	feature_mask = (msr & MSR_AMD64_SEV_ENABLED) ? AMD_SEV_BIT : AMD_SME_BIT;
+	snp_enabled = msr & MSR_AMD64_SEV_SNP_ENABLED;
+	feature_mask = snp_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))
+	/*
+	 * The SEV-SNP CC blob should never be present unless SEV-SNP is enabled.
+	 *
+	 * The SEV-SNP CC blob should be present and parsing CC blob should
+	 * succeed when SEV-SNP is enabled.
+	 */
+	if ((snp && !snp_enabled) ||
+	    (!snp && snp_enabled))
 		snp_abort();
 
 	/* Check if memory encryption is enabled */
-- 
2.34.1


1. https://lore.kernel.org/lkml/20240416144542.GFZh6PFjPNT9Zt3iUl@fat_crate.local/