diff mbox series

[v6,09/42] x86/sev: Check SEV-SNP features support

Message ID 20211008180453.462291-10-brijesh.singh@amd.com (mailing list archive)
State New
Headers show
Series Add AMD Secure Nested Paging (SEV-SNP) Guest Support | expand

Commit Message

Brijesh Singh Oct. 8, 2021, 6:04 p.m. UTC 
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@amd.com>
---
 arch/x86/boot/compressed/sev.c    | 16 ++++++++++++++--
 arch/x86/include/asm/sev-common.h |  3 +++
 arch/x86/kernel/sev.c             |  8 ++++++--
 3 files changed, 23 insertions(+), 4 deletions(-)

Comments

Borislav Petkov Oct. 19, 2021, 2:47 p.m. UTC | #1 
On Fri, Oct 08, 2021 at 01:04:20PM -0500, Brijesh Singh wrote:
> +static bool do_early_sev_setup(void)
>  {
>  	if (!sev_es_negotiate_protocol())
>  		sev_es_terminate(SEV_TERM_SET_GEN, GHCB_SEV_ES_PROT_UNSUPPORTED);
>  
> +	/*
> +	 * If SEV-SNP is enabled, then check if the hypervisor supports the SEV-SNP
> +	 * features.

This and the other comment should say something along the lines of:

"SNP is supported in v2 of the GHCB spec which mandates support for HV
features."

because it wasn't clear to me why we're enforcing that support here.

Thx.
diff mbox series

Patch

diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c
index 7760959fe96d..8b0f892c072b 100644
--- a/arch/x86/boot/compressed/sev.c
+++ b/arch/x86/boot/compressed/sev.c
@@ -119,11 +119,23 @@  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);
 
+	/*
+	 * 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 +186,7 @@  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 427b1c6d08a8..2290fbcc1844 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -631,12 +631,16 @@  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;
 
+	/* If SNP is active, make sure that hypervisor supports the feature. */
+	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.
@@ -1444,7 +1448,7 @@  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);