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Subject[PATCH Part1 RFC v4 06/36] x86/sev: check SEV-SNP features support
Date
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 | 26 ++++++++++++++++++++++++--
arch/x86/include/asm/sev-common.h | 3 +++
arch/x86/kernel/sev.c | 8 ++++++--
3 files changed, 33 insertions(+), 4 deletions(-)

diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c
index 7760959fe96d..7be325d9b09f 100644
--- a/arch/x86/boot/compressed/sev.c
+++ b/arch/x86/boot/compressed/sev.c
@@ -25,6 +25,7 @@

struct ghcb boot_ghcb_page __aligned(PAGE_SIZE);
struct ghcb *boot_ghcb;
+static u64 msr_sev_status;

/*
* Copy a version of this function here - insn-eval.c can't be used in
@@ -119,11 +120,32 @@ 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)
+{
+ unsigned long low, high;
+
+ if (!msr_sev_status) {
+ asm volatile("rdmsr\n"
+ : "=a" (low), "=d" (high)
+ : "c" (MSR_AMD64_SEV));
+ msr_sev_status = (high << 32) | low;
+ }
+
+ return msr_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 +196,7 @@ 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 e75e29c05f59..8abc5eb7ca3d 100644
--- a/arch/x86/include/asm/sev-common.h
+++ b/arch/x86/include/asm/sev-common.h
@@ -54,6 +54,8 @@
#define GHCB_MSR_HV_FT_RESP_VAL(v) \
(((unsigned long)((v) >> GHCB_MSR_HV_FT_POS) & GHCB_MSR_HV_FT_MASK))

+#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
@@ -67,6 +69,7 @@
#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

#define GHCB_RESP_CODE(v) ((v) & GHCB_MSR_INFO_MASK)

diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index 0245fe986615..504169f1966b 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -665,12 +665,16 @@ 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 (sev_feature_enabled(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.
@@ -1479,7 +1483,7 @@ 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 == NULL && !setup_ghcb()))
sev_es_terminate(SEV_TERM_SET_GEN, GHCB_SEV_ES_GEN_REQ);

vc_ghcb_invalidate(boot_ghcb);
--
2.17.1
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