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 | 21 +++++++++++++++++++++
arch/x86/kernel/sev-shared.c | 13 ++++++++++++-
arch/x86/kernel/sev.c | 4 ++++
3 files changed, 37 insertions(+), 1 deletion(-)
diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c
index 6d9055427f37..7badbeb6cb95 100644
--- a/arch/x86/boot/compressed/sev.c
+++ b/arch/x86/boot/compressed/sev.c
@@ -25,6 +25,8 @@
struct ghcb boot_ghcb_page __aligned(PAGE_SIZE);
struct ghcb *boot_ghcb;
+static u64 sev_status_val;
+static bool sev_status_checked;
/*
* Copy a version of this function here - insn-eval.c can't be used in
@@ -119,11 +121,30 @@ static enum es_result vc_read_mem(struct es_em_ctxt *ctxt,
/* Include code for early handlers */
#include "../../kernel/sev-shared.c"
+static inline bool sev_snp_enabled(void)
+{
+ unsigned long low, high;
+
+ if (!sev_status_checked) {
+ asm volatile("rdmsr\n"
+ : "=a" (low), "=d" (high)
+ : "c" (MSR_AMD64_SEV));
+ sev_status_val = (high << 32) | low;
+ sev_status_checked = true;
+ }
+
+ return sev_status_val & MSR_AMD64_SEV_SNP_ENABLED ? true : false;
+}
+
static bool early_setup_sev_es(void)
{
if (!sev_es_negotiate_protocol())
sev_es_terminate(0, GHCB_SEV_ES_REASON_PROTOCOL_UNSUPPORTED);
+ /* If SEV-SNP is enabled then check if the hypervisor supports the SEV-SNP features. */
+ if (sev_snp_enabled() && !sev_snp_check_hypervisor_features())
+ sev_es_terminate(0, GHCB_SEV_ES_REASON_SNP_UNSUPPORTED);
+
if (set_page_decrypted((unsigned long)&boot_ghcb_page))
return false;
diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c
index 3f9b06a04395..085d3d724bc8 100644
--- a/arch/x86/kernel/sev-shared.c
+++ b/arch/x86/kernel/sev-shared.c
@@ -32,7 +32,18 @@ static bool __init sev_es_check_cpu_features(void)
return true;
}
-+static void __noreturn sev_es_terminate(unsigned int set, unsigned int reason)
+static bool __init sev_snp_check_hypervisor_features(void)
+{
+ if (ghcb_version < 2)
+ return false;
+
+ if (!(hv_features & GHCB_HV_FEATURES_SNP))
+ return false;
+
+ return true;
+}
+
+static void __noreturn sev_es_terminate(unsigned int set, unsigned int reason)
{
u64 val = GHCB_MSR_TERM_REQ;
diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index 97be0fe666ab..8c8c939a1754 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -609,6 +609,10 @@ static bool __init sev_es_setup_ghcb(void)
if (!sev_es_negotiate_protocol())
return false;
+ /* If SNP is active, make sure that hypervisor supports the feature. */
+ if (sev_snp_active() && !sev_snp_check_hypervisor_features())
+ sev_es_terminate(0, GHCB_SEV_ES_REASON_SNP_UNSUPPORTED);
+
/*
* Clear the boot_ghcb. The first exception comes in before the bss
* section is cleared.
--
2.17.1
