x86/sev: Add SEV-SNP feature detection/setup

Initial/preliminary detection of SEV-SNP is done via the Confidential
Computing blob. Check for it prior to the normal SEV/SME feature
initialization, and add some sanity checks to confirm it agrees with
SEV-SNP CPUID/MSR bits.

Signed-off-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20220307213356.2797205-39-brijesh.singh@amd.com

arch/x86/boot/compressed/sev.c

@@ -352,33 +352,6 @@ static struct cc_blob_sev_info *find_cc_blob_efi(struct boot_params *bp)
 								EFI_CC_BLOB_GUID);
 }
 
-struct cc_setup_data {
-	struct setup_data header;
-	u32 cc_blob_address;
-};
-
-/*
- * Search for a Confidential Computing blob passed in as a setup_data entry
- * via the Linux Boot Protocol.
- */
-static struct cc_blob_sev_info *find_cc_blob_setup_data(struct boot_params *bp)
-{
-	struct cc_setup_data *sd = NULL;
-	struct setup_data *hdr;
-
-	hdr = (struct setup_data *)bp->hdr.setup_data;
-
-	while (hdr) {
-		if (hdr->type == SETUP_CC_BLOB) {
-			sd = (struct cc_setup_data *)hdr;
-			return (struct cc_blob_sev_info *)(unsigned long)sd->cc_blob_address;
-		}
-		hdr = (struct setup_data *)hdr->next;
-	}
-
-	return NULL;
-}
-
 /*
  * Initial set up of SNP relies on information provided by the
  * Confidential Computing blob, which can be passed to the boot kernel

arch/x86/include/asm/sev.h

@@ -153,6 +153,7 @@ void snp_set_memory_shared(unsigned long vaddr, unsigned int npages);
 void snp_set_memory_private(unsigned long vaddr, unsigned int npages);
 void snp_set_wakeup_secondary_cpu(void);
 bool snp_init(struct boot_params *bp);
+void snp_abort(void);
 #else
 static inline void sev_es_ist_enter(struct pt_regs *regs) { }
 static inline void sev_es_ist_exit(void) { }
@@ -171,6 +172,7 @@ static inline void snp_set_memory_shared(unsigned long vaddr, unsigned int npage
 static inline void snp_set_memory_private(unsigned long vaddr, unsigned int npages) { }
 static inline void snp_set_wakeup_secondary_cpu(void) { }
 static inline bool snp_init(struct boot_params *bp) { return false; }
+static inline void snp_abort(void) { }
 #endif
 
 #endif

arch/x86/kernel/sev-shared.c

@@ -937,3 +937,30 @@ static enum es_result vc_handle_rdtsc(struct ghcb *ghcb,
 
 	return ES_OK;
 }
+
+struct cc_setup_data {
+	struct setup_data header;
+	u32 cc_blob_address;
+};
+
+/*
+ * Search for a Confidential Computing blob passed in as a setup_data entry
+ * via the Linux Boot Protocol.
+ */
+static struct cc_blob_sev_info *find_cc_blob_setup_data(struct boot_params *bp)
+{
+	struct cc_setup_data *sd = NULL;
+	struct setup_data *hdr;
+
+	hdr = (struct setup_data *)bp->hdr.setup_data;
+
+	while (hdr) {
+		if (hdr->type == SETUP_CC_BLOB) {
+			sd = (struct cc_setup_data *)hdr;
+			return (struct cc_blob_sev_info *)(unsigned long)sd->cc_blob_address;
+		}
+		hdr = (struct setup_data *)hdr->next;
+	}
+
+	return NULL;
+}

arch/x86/kernel/sev.c

@@ -1974,3 +1974,67 @@ fail:
 	while (true)
 		halt();
 }
+
+/*
+ * Initial set up of SNP relies on information provided by the
+ * Confidential Computing blob, which can be passed to the kernel
+ * in the following ways, depending on how it is booted:
+ *
+ * - when booted via the boot/decompress kernel:
+ *   - via boot_params
+ *
+ * - when booted directly by firmware/bootloader (e.g. CONFIG_PVH):
+ *   - via a setup_data entry, as defined by the Linux Boot Protocol
+ *
+ * Scan for the blob in that order.
+ */
+static __init struct cc_blob_sev_info *find_cc_blob(struct boot_params *bp)
+{
+	struct cc_blob_sev_info *cc_info;
+
+	/* Boot kernel would have passed the CC blob via boot_params. */
+	if (bp->cc_blob_address) {
+		cc_info = (struct cc_blob_sev_info *)(unsigned long)bp->cc_blob_address;
+		goto found_cc_info;
+	}
+
+	/*
+	 * If kernel was booted directly, without the use of the
+	 * boot/decompression kernel, the CC blob may have been passed via
+	 * setup_data instead.
+	 */
+	cc_info = find_cc_blob_setup_data(bp);
+	if (!cc_info)
+		return NULL;
+
+found_cc_info:
+	if (cc_info->magic != CC_BLOB_SEV_HDR_MAGIC)
+		snp_abort();
+
+	return cc_info;
+}
+
+bool __init snp_init(struct boot_params *bp)
+{
+	struct cc_blob_sev_info *cc_info;
+
+	if (!bp)
+		return false;
+
+	cc_info = find_cc_blob(bp);
+	if (!cc_info)
+		return false;
+
+	/*
+	 * The CC blob will be used later to access the secrets page. Cache
+	 * it here like the boot kernel does.
+	 */
+	bp->cc_blob_address = (u32)(unsigned long)cc_info;
+
+	return true;
+}
+
+void __init snp_abort(void)
+{
+	sev_es_terminate(SEV_TERM_SET_GEN, GHCB_SNP_UNSUPPORTED);
+}

arch/x86/mm/mem_encrypt_identity.c

@@ -45,6 +45,7 @@
 #include <asm/sections.h>
 #include <asm/cmdline.h>
 #include <asm/coco.h>
+#include <asm/sev.h>
 
 #include "mm_internal.h"
 
@@ -509,8 +510,11 @@ void __init sme_enable(struct boot_params *bp)
 	bool active_by_default;
 	unsigned long me_mask;
 	char buffer[16];
+	bool snp;
 	u64 msr;
 
+	snp = snp_init(bp);
+
 	/* Check for the SME/SEV support leaf */
 	eax = 0x80000000;
 	ecx = 0;
@@ -542,6 +546,10 @@ void __init sme_enable(struct boot_params *bp)
 	sev_status   = __rdmsr(MSR_AMD64_SEV);
 	feature_mask = (sev_status & 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 && !(sev_status & MSR_AMD64_SEV_SNP_ENABLED))
+		snp_abort();
+
 	/* Check if memory encryption is enabled */
 	if (feature_mask == AMD_SME_BIT) {
 		/*