crypto: ccp - Introduce new API interface to indicate SEV-SNP Ciphertext hiding feature

Implement an API that checks the overall feature support for SEV-SNP
ciphertext hiding.

This API verifies both the support of the SEV firmware for the feature
and its enablement in the platform's BIOS.

Reviewed-by: Tom Lendacky <[email protected]>
Signed-off-by: Ashish Kalra <[email protected]>
Reviewed-by: Kim Phillips <[email protected]>
Signed-off-by: Herbert Xu <[email protected]>

Author: ashkalra

drivers/crypto/ccp/sev-dev.c

@@ -1074,6 +1074,27 @@ static void snp_set_hsave_pa(void *arg)
 	wrmsrq(MSR_VM_HSAVE_PA, 0);
 }
 
+bool sev_is_snp_ciphertext_hiding_supported(void)
+{
+	struct psp_device *psp = psp_master;
+	struct sev_device *sev;
+
+	if (!psp || !psp->sev_data)
+		return false;
+
+	sev = psp->sev_data;
+
+	/*
+	 * Feature information indicates if CipherTextHiding feature is
+	 * supported by the SEV firmware and additionally platform status
+	 * indicates if CipherTextHiding feature is enabled in the
+	 * Platform BIOS.
+	 */
+	return ((sev->snp_feat_info_0.ecx & SNP_CIPHER_TEXT_HIDING_SUPPORTED) &&
+		 sev->snp_plat_status.ciphertext_hiding_cap);
+}
+EXPORT_SYMBOL_GPL(sev_is_snp_ciphertext_hiding_supported);
+
 static int snp_get_platform_data(struct sev_device *sev, int *error)
 {
 	struct sev_data_snp_feature_info snp_feat_info;

include/linux/psp-sev.h

@@ -843,6 +843,8 @@ struct snp_feature_info {
 	u32 edx;
 } __packed;
 
+#define SNP_CIPHER_TEXT_HIDING_SUPPORTED	BIT(3)
+
 #ifdef CONFIG_CRYPTO_DEV_SP_PSP
 
 /**
@@ -986,6 +988,7 @@ void *psp_copy_user_blob(u64 uaddr, u32 len);
 void *snp_alloc_firmware_page(gfp_t mask);
 void snp_free_firmware_page(void *addr);
 void sev_platform_shutdown(void);
+bool sev_is_snp_ciphertext_hiding_supported(void);
 
 #else	/* !CONFIG_CRYPTO_DEV_SP_PSP */
 
@@ -1022,6 +1025,8 @@ static inline void snp_free_firmware_page(void *addr) { }
 
 static inline void sev_platform_shutdown(void) { }
 
+static inline bool sev_is_snp_ciphertext_hiding_supported(void) { return false; }
+
 #endif	/* CONFIG_CRYPTO_DEV_SP_PSP */
 
 #endif	/* __PSP_SEV_H__ */