Re: [PATCH v11 06/20] x86/sev: Handle failures from snp_init()

From: Nikunj A. Dadhania
Date: Wed Aug 28 2024 - 00:48:25 EST


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@xxxxxxx>
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@xxxxxxx>
---
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/