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From:   Brijesh Singh <brijesh.singh@amd.com>
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        Brijesh Singh <brijesh.singh@amd.com>
Subject: [PATCH v8 31/40] x86/compressed: add SEV-SNP feature detection/setup
Date:   Fri, 10 Dec 2021 09:43:23 -0600
Message-ID: <20211210154332.11526-32-brijesh.singh@amd.com>
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From: Michael Roth <michael.roth@amd.com>

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>
---
 arch/x86/boot/compressed/sev.c | 91 +++++++++++++++++++++++++++++++++-
 arch/x86/include/asm/sev.h     | 13 +++++
 arch/x86/kernel/sev-shared.c   | 34 +++++++++++++
 3 files changed, 137 insertions(+), 1 deletion(-)

diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c
index 3514feb5b226..93e125da12cf 100644
--- a/arch/x86/boot/compressed/sev.c
+++ b/arch/x86/boot/compressed/sev.c
@@ -291,6 +291,13 @@ static void enforce_vmpl0(void)
 void sev_enable(struct boot_params *bp)
 {
 	unsigned int eax, ebx, ecx, edx;
+	bool snp;
+
+	/*
+	 * Setup/preliminary detection of SEV-SNP. This will be sanity-checked
+	 * against CPUID/MSR values later.
+	 */
+	snp = snp_init(bp);
 
 	/* Check for the SME/SEV support leaf */
 	eax = 0x80000000;
@@ -311,8 +318,11 @@ void sev_enable(struct boot_params *bp)
 	ecx = 0;
 	native_cpuid(&eax, &ebx, &ecx, &edx);
 	/* Check whether SEV is supported */
-	if (!(eax & BIT(1)))
+	if (!(eax & BIT(1))) {
+		if (snp)
+			error("SEV-SNP support indicated by CC blob, but not CPUID.");
 		return;
+	}
 
 	/* Set the SME mask if this is an SEV guest. */
 	sev_status   = rd_sev_status_msr();
@@ -337,5 +347,84 @@ void sev_enable(struct boot_params *bp)
 		enforce_vmpl0();
 	}
 
+	if (snp && !(sev_status & MSR_AMD64_SEV_SNP_ENABLED))
+		error("SEV-SNP supported indicated by CC blob, but not SEV status MSR.");
+
 	sme_me_mask = BIT_ULL(ebx & 0x3f);
 }
+
+/* Search for Confidential Computing blob in the EFI config table. */
+static struct cc_blob_sev_info *snp_find_cc_blob_efi(struct boot_params *bp)
+{
+	struct cc_blob_sev_info *cc_info;
+	unsigned long conf_table_pa;
+	unsigned int conf_table_len;
+	bool efi_64;
+	int ret;
+
+	ret = efi_get_conf_table(bp, &conf_table_pa, &conf_table_len, &efi_64);
+	if (ret)
+		return NULL;
+
+	ret = efi_find_vendor_table(conf_table_pa, conf_table_len,
+				    EFI_CC_BLOB_GUID, efi_64,
+				    (unsigned long *)&cc_info);
+	if (ret)
+		return NULL;
+
+	return cc_info;
+}
+
+/*
+ * Initial set up of SEV-SNP relies on information provided by the
+ * Confidential Computing blob, which can be passed to the boot kernel
+ * by firmware/bootloader in the following ways:
+ *
+ * - via an entry in the EFI config table
+ * - via a setup_data structure, as defined by the Linux Boot Protocol
+ *
+ * Scan for the blob in that order.
+ */
+static struct cc_blob_sev_info *snp_find_cc_blob(struct boot_params *bp)
+{
+	struct cc_blob_sev_info *cc_info;
+
+	cc_info = snp_find_cc_blob_efi(bp);
+	if (cc_info)
+		goto found_cc_info;
+
+	cc_info = snp_find_cc_blob_setup_data(bp);
+	if (!cc_info)
+		return NULL;
+
+found_cc_info:
+	if (cc_info->magic != CC_BLOB_SEV_HDR_MAGIC)
+		sev_es_terminate(0, GHCB_SNP_UNSUPPORTED);
+
+	return cc_info;
+}
+
+bool snp_init(struct boot_params *bp)
+{
+	struct cc_blob_sev_info *cc_info;
+
+	if (!bp)
+		return false;
+
+	cc_info = snp_find_cc_blob(bp);
+	if (!cc_info)
+		return false;
+
+	/*
+	 * Pass run-time kernel a pointer to CC info via boot_params so EFI
+	 * config table doesn't need to be searched again during early startup
+	 * phase.
+	 */
+	bp->cc_blob_address = (u32)(unsigned long)cc_info;
+
+	/*
+	 * Indicate SEV-SNP based on presence of SEV-SNP-specific CC blob.
+	 * Subsequent checks will verify SEV-SNP CPUID/MSR bits.
+	 */
+	return true;
+}
diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
index f42fbe3c332f..cd189c20bcc4 100644
--- a/arch/x86/include/asm/sev.h
+++ b/arch/x86/include/asm/sev.h
@@ -11,6 +11,7 @@
 #include <linux/types.h>
 #include <asm/insn.h>
 #include <asm/sev-common.h>
+#include <asm/bootparam.h>
 
 #define GHCB_PROTOCOL_MIN	1ULL
 #define GHCB_PROTOCOL_MAX	2ULL
@@ -145,6 +146,17 @@ void __init snp_prep_memory(unsigned long paddr, unsigned int sz, enum psc_op op
 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);
+/*
+ * TODO: These are exported only temporarily while boot/compressed/sev.c is
+ * the only user. This is to avoid unused function warnings for kernel/sev.c
+ * during the build of kernel proper.
+ *
+ * Once the code is added to consume these in kernel proper these functions
+ * can be moved back to being statically-scoped to units that pull in
+ * sev-shared.c via #include and these declarations can be dropped.
+ */
+struct cc_blob_sev_info *snp_find_cc_blob_setup_data(struct boot_params *bp);
 #else
 static inline void sev_es_ist_enter(struct pt_regs *regs) { }
 static inline void sev_es_ist_exit(void) { }
@@ -162,6 +174,7 @@ static inline void __init snp_prep_memory(unsigned long paddr, unsigned int sz,
 static inline void snp_set_memory_shared(unsigned long vaddr, unsigned int npages) { }
 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; }
 #endif
 
 #endif
diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c
index dabb425498e0..bd58a4ce29c8 100644
--- a/arch/x86/kernel/sev-shared.c
+++ b/arch/x86/kernel/sev-shared.c
@@ -934,3 +934,37 @@ 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;
+};
+
+static struct cc_setup_data *get_cc_setup_data(struct boot_params *bp)
+{
+	struct setup_data *hdr = (struct setup_data *)bp->hdr.setup_data;
+
+	while (hdr) {
+		if (hdr->type == SETUP_CC_BLOB)
+			return (struct cc_setup_data *)hdr;
+		hdr = (struct setup_data *)hdr->next;
+	}
+
+	return NULL;
+}
+
+/*
+ * Search for a Confidential Computing blob passed in as a setup_data entry
+ * via the Linux Boot Protocol.
+ */
+struct cc_blob_sev_info *
+snp_find_cc_blob_setup_data(struct boot_params *bp)
+{
+	struct cc_setup_data *sd;
+
+	sd = get_cc_setup_data(bp);
+	if (!sd)
+		return NULL;
+
+	return (struct cc_blob_sev_info *)(unsigned long)sd->cc_blob_address;
+}
-- 
2.25.1