[PATCH v6 1/9] KVM: SEV: Disable SEV-SNP on FW validation failure

["Pratik R. Sampat" <prsampat@amd.com>]

On incompatible firmware versions, SEV-SNP support is pulled and the
setup is not performed. However, the platform and subsequently the KVM
capability may continue to advertise support for it. Disable support for
SEV-SNP if the FW version validation fails.

Fixes: 1dfe571c12cf ("KVM: SEV: Add initial SEV-SNP support")
Suggested-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Nikunj A Dadhania <nikunj@amd.com>
Tested-by: Srikanth Aithal <sraithal@amd.com>
Signed-off-by: Pratik R. Sampat <prsampat@amd.com>
---
v5..v6:

* Collected tags from Nikunj and Srikanth.
---
 arch/x86/kvm/svm/sev.c       | 4 +++-
 drivers/crypto/ccp/sev-dev.c | 6 ++++++
 include/linux/psp-sev.h      | 3 +++
 3 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 0f04f365885c..b709c2f0945c 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -3040,7 +3040,9 @@ void __init sev_hardware_setup(void)
 	sev_es_asid_count = min_sev_asid - 1;
 	WARN_ON_ONCE(misc_cg_set_capacity(MISC_CG_RES_SEV_ES, sev_es_asid_count));
 	sev_es_supported = true;
-	sev_snp_supported = sev_snp_enabled && cc_platform_has(CC_ATTR_HOST_SEV_SNP);
+	sev_snp_supported = (sev_snp_enabled &&
+			    cc_platform_has(CC_ATTR_HOST_SEV_SNP) &&
+			    snp_fw_valid());
 
 out:
 	if (boot_cpu_has(X86_FEATURE_SEV))
diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
index af018afd9cd7..b45cd60c19b0 100644
--- a/drivers/crypto/ccp/sev-dev.c
+++ b/drivers/crypto/ccp/sev-dev.c
@@ -122,6 +122,12 @@ static inline bool sev_version_greater_or_equal(u8 maj, u8 min)
 	return false;
 }
 
+bool snp_fw_valid(void)
+{
+	return sev_version_greater_or_equal(SNP_MIN_API_MAJOR, SNP_MIN_API_MINOR);
+}
+EXPORT_SYMBOL_GPL(snp_fw_valid);
+
 static void sev_irq_handler(int irq, void *data, unsigned int status)
 {
 	struct sev_device *sev = data;
diff --git a/include/linux/psp-sev.h b/include/linux/psp-sev.h
index 903ddfea8585..e841a8fbbb15 100644
--- a/include/linux/psp-sev.h
+++ b/include/linux/psp-sev.h
@@ -945,6 +945,7 @@ int sev_do_cmd(int cmd, void *data, int *psp_ret);
 void *psp_copy_user_blob(u64 uaddr, u32 len);
 void *snp_alloc_firmware_page(gfp_t mask);
 void snp_free_firmware_page(void *addr);
+bool snp_fw_valid(void);
 
 #else	/* !CONFIG_CRYPTO_DEV_SP_PSP */
 
@@ -979,6 +980,8 @@ static inline void *snp_alloc_firmware_page(gfp_t mask)
 
 static inline void snp_free_firmware_page(void *addr) { }
 
+static inline bool snp_fw_valid(void) { return false; }
+
 #endif	/* CONFIG_CRYPTO_DEV_SP_PSP */
 
 #endif	/* __PSP_SEV_H__ */
-- 
2.43.0