[kvm-unit-tests,10/13] x86: AMD SEV-ES: Handle RDTSC/RDTSCP #VC

Commit Message

Varad Gautam Jan. 20, 2022, 12:51 p.m. UTC

Using Linux's RDTSC #VC processing logic.

Signed-off-by: Varad Gautam <[e-mail]>
---
 lib/x86/amd_sev_vc.c | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

Comments

Sean Christopherson Feb. 7, 2022, 9:17 p.m. UTC | #1

On Thu, Jan 20, 2022, Varad Gautam wrote:
> Using Linux's RDTSC #VC processing logic.

I vote we drop this patch and instead treat #VC on RDTSC{,P} as a failure.  KVM
should never intercept RDTSC or RDTSCP except to inject #UD on RDTSCP, and IMO
any hypervisor that deviates from the behavior for an SEV-ES guest is being
malicious.  That the SEV spec even allows reflecting them as #VC is ridiculous.

Patch

diff --git a/lib/x86/amd_sev_vc.c b/lib/x86/amd_sev_vc.c
index 91f57e0..45b7ad1 100644
--- a/lib/x86/amd_sev_vc.c
+++ b/lib/x86/amd_sev_vc.c
@@ -153,6 +153,29 @@  static enum es_result vc_handle_cpuid(struct ghcb *ghcb,
 	return ES_OK;
 }
 
+static enum es_result vc_handle_rdtsc(struct ghcb *ghcb,
+				      struct es_em_ctxt *ctxt,
+				      unsigned long exit_code)
+{
+	bool rdtscp = (exit_code == SVM_EXIT_RDTSCP);
+	enum es_result ret;
+
+	ret = sev_es_ghcb_hv_call(ghcb, ctxt, exit_code, 0, 0);
+	if (ret != ES_OK)
+		return ret;
+
+	if (!(ghcb_rax_is_valid(ghcb) && ghcb_rdx_is_valid(ghcb) &&
+	     (!rdtscp || ghcb_rcx_is_valid(ghcb))))
+		return ES_VMM_ERROR;
+
+	ctxt->regs->rax = ghcb->save.rax;
+	ctxt->regs->rdx = ghcb->save.rdx;
+	if (rdtscp)
+		ctxt->regs->rcx = ghcb->save.rcx;
+
+	return ES_OK;
+}
+
 static enum es_result vc_handle_exitcode(struct es_em_ctxt *ctxt,
 					 struct ghcb *ghcb,
 					 unsigned long exit_code)
@@ -166,6 +189,10 @@  static enum es_result vc_handle_exitcode(struct es_em_ctxt *ctxt,
 	case SVM_EXIT_CPUID:
 		result = vc_handle_cpuid(ghcb, ctxt);
 		break;
+	case SVM_EXIT_RDTSC:
+	case SVM_EXIT_RDTSCP:
+		result = vc_handle_rdtsc(ghcb, ctxt, exit_code);
+		break;
 	default:
 		/*
 		 * Unexpected #VC exception