[PATCH v7 11/45] x86/sev: Check SEV-SNP features support

[Brijesh Singh]

Version 2 of the GHCB specification added the advertisement of features
that are supported by the hypervisor. If hypervisor supports the SEV-SNP
then it must set the SEV-SNP features bit to indicate that the base
SEV-SNP is supported.

Check the SEV-SNP feature while establishing the GHCB, if failed,
terminate the guest.

Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
---
 arch/x86/boot/compressed/sev.c    | 17 +++++++++++++++--
 arch/x86/include/asm/sev-common.h |  3 +++
 arch/x86/kernel/sev.c             | 12 ++++++++++--
 3 files changed, 28 insertions(+), 4 deletions(-)

diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c
index 78f8502e09b5..e525fa74a551 100644
--- a/arch/x86/boot/compressed/sev.c
+++ b/arch/x86/boot/compressed/sev.c
@@ -119,11 +119,24 @@ static enum es_result vc_read_mem(struct es_em_ctxt *ctxt,
 /* Include code for early handlers */
 #include "../../kernel/sev-shared.c"
 
-static bool early_setup_sev_es(void)
+static inline bool sev_snp_enabled(void)
+{
+	return sev_status & MSR_AMD64_SEV_SNP_ENABLED;
+}
+
+static bool do_early_sev_setup(void)
 {
 	if (!sev_es_negotiate_protocol())
 		sev_es_terminate(SEV_TERM_SET_GEN, GHCB_SEV_ES_PROT_UNSUPPORTED);
 
+	/*
+	 * SNP is supported in v2 of the GHCB spec which mandates support for HV
+	 * features. If SEV-SNP is enabled, then check if the hypervisor supports
+	 * the SEV-SNP features.
+	 */
+	if (sev_snp_enabled() && !(sev_hv_features & GHCB_HV_FT_SNP))
+		sev_es_terminate(SEV_TERM_SET_GEN, GHCB_SNP_UNSUPPORTED);
+
 	if (set_page_decrypted((unsigned long)&boot_ghcb_page))
 		return false;
 
@@ -174,7 +187,7 @@ void do_boot_stage2_vc(struct pt_regs *regs, unsigned long exit_code)
 	struct es_em_ctxt ctxt;
 	enum es_result result;
 
-	if (!boot_ghcb && !early_setup_sev_es())
+	if (!boot_ghcb && !do_early_sev_setup())
 		sev_es_terminate(SEV_TERM_SET_GEN, GHCB_SEV_ES_GEN_REQ);
 
 	vc_ghcb_invalidate(boot_ghcb);
diff --git a/arch/x86/include/asm/sev-common.h b/arch/x86/include/asm/sev-common.h
index 891569c07ed7..f80a3cde2086 100644
--- a/arch/x86/include/asm/sev-common.h
+++ b/arch/x86/include/asm/sev-common.h
@@ -64,6 +64,8 @@
 	/* GHCBData[63:12] */				\
 	(((u64)(v) & GENMASK_ULL(63, 12)) >> 12)
 
+#define GHCB_HV_FT_SNP			BIT_ULL(0)
+
 #define GHCB_MSR_TERM_REQ		0x100
 #define GHCB_MSR_TERM_REASON_SET_POS	12
 #define GHCB_MSR_TERM_REASON_SET_MASK	0xf
@@ -80,6 +82,7 @@
 #define SEV_TERM_SET_GEN		0
 #define GHCB_SEV_ES_GEN_REQ		0
 #define GHCB_SEV_ES_PROT_UNSUPPORTED	1
+#define GHCB_SNP_UNSUPPORTED		2
 
 /* Linux-specific reason codes (used with reason set 1) */
 #define SEV_TERM_SET_LINUX		1
diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index fb48e4ddd474..80a41e413cb8 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -627,12 +627,20 @@ static enum es_result vc_handle_msr(struct ghcb *ghcb, struct es_em_ctxt *ctxt)
  * This function runs on the first #VC exception after the kernel
  * switched to virtual addresses.
  */
-static bool __init sev_es_setup_ghcb(void)
+static bool __init setup_ghcb(void)
 {
 	/* First make sure the hypervisor talks a supported protocol. */
 	if (!sev_es_negotiate_protocol())
 		return false;
 
+	/*
+	 * SNP is supported in v2 of the GHCB spec which mandates support for HV
+	 * features. If SEV-SNP is enabled, then check if the hypervisor supports
+	 * the SEV-SNP features.
+	 */
+	if (cc_platform_has(CC_ATTR_SEV_SNP) && !(sev_hv_features & GHCB_HV_FT_SNP))
+		sev_es_terminate(SEV_TERM_SET_GEN, GHCB_SNP_UNSUPPORTED);
+
 	/*
 	 * Clear the boot_ghcb. The first exception comes in before the bss
 	 * section is cleared.
@@ -1453,7 +1461,7 @@ bool __init handle_vc_boot_ghcb(struct pt_regs *regs)
 	enum es_result result;
 
 	/* Do initial setup or terminate the guest */
-	if (unlikely(boot_ghcb == NULL && !sev_es_setup_ghcb()))
+	if (unlikely(!boot_ghcb && !setup_ghcb()))
 		sev_es_terminate(SEV_TERM_SET_GEN, GHCB_SEV_ES_GEN_REQ);
 
 	vc_ghcb_invalidate(boot_ghcb);
-- 
2.25.1