[tip: x86/sev] x86/sev: Do not handle #VC for DR7 read/write

[tip-bot2 for Alexey Kardashevskiy]

The following commit has been merged into the x86/sev branch of tip:

Commit-ID:     e221804dad4e6fe3a0cf192ba3c42cd2f328bdac
Gitweb:        https://git.kernel.org/tip/e221804dad4e6fe3a0cf192ba3c42cd2f328bdac
Author:        Alexey Kardashevskiy <aik@xxxxxxx>
AuthorDate:    Wed, 16 Aug 2023 12:21:22 +10:00
Committer:     Borislav Petkov (AMD) <bp@xxxxxxxxx>
CommitterDate: Wed, 16 Aug 2023 10:13:42 +02:00

x86/sev: Do not handle #VC for DR7 read/write

With MSR_AMD64_SEV_DEBUG_SWAP enabled, the guest is not expected to
receive a #VC for reads or writes of DR7.

Update the SNP_FEATURES_PRESENT mask with MSR_AMD64_SNP_DEBUG_SWAP so
an SNP guest doesn't gracefully terminate during SNP feature negotiation
if MSR_AMD64_SEV_DEBUG_SWAP is enabled.

Since a guest is not expected to receive a #VC on DR7 accesses when
MSR_AMD64_SEV_DEBUG_SWAP is enabled, return an error from the #VC
handler in this situation.

Signed-off-by: Alexey Kardashevskiy <aik@xxxxxxx>
Signed-off-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
Reviewed-by: Carlos Bilbao <carlos.bilbao@xxxxxxx>
Reviewed-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
Reviewed-by: Pankaj Gupta <pankaj.gupta@xxxxxxx>
Link: https://lore.kernel.org/r/20230816022122.981998-1-aik@xxxxxxx
---
 arch/x86/boot/compressed/sev.c | 2 +-
 arch/x86/kernel/sev.c          | 6 ++++++
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c
index c3e343b..e83e710 100644
--- a/arch/x86/boot/compressed/sev.c
+++ b/arch/x86/boot/compressed/sev.c
@@ -365,7 +365,7 @@ static void enforce_vmpl0(void)
  * by the guest kernel. As and when a new feature is implemented in the
  * guest kernel, a corresponding bit should be added to the mask.
  */
-#define SNP_FEATURES_PRESENT (0)
+#define SNP_FEATURES_PRESENT	MSR_AMD64_SNP_DEBUG_SWAP
 
 void snp_check_features(void)
 {
diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index 1ee7bed..d380c93 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -1575,6 +1575,9 @@ static enum es_result vc_handle_dr7_write(struct ghcb *ghcb,
 	long val, *reg = vc_insn_get_rm(ctxt);
 	enum es_result ret;
 
+	if (sev_status & MSR_AMD64_SNP_DEBUG_SWAP)
+		return ES_VMM_ERROR;
+
 	if (!reg)
 		return ES_DECODE_FAILED;
 
@@ -1612,6 +1615,9 @@ static enum es_result vc_handle_dr7_read(struct ghcb *ghcb,
 	struct sev_es_runtime_data *data = this_cpu_read(runtime_data);
 	long *reg = vc_insn_get_rm(ctxt);
 
+	if (sev_status & MSR_AMD64_SNP_DEBUG_SWAP)
+		return ES_VMM_ERROR;
+
 	if (!reg)
 		return ES_DECODE_FAILED;