[PATCH v2 1/2] KVM: Exception during emulation decode should propagate

[Nadav Amit]

An exception might occur during decode (e.g., #PF during fetch).
Currently, the exception is ignored and emulation is performed.
Instead, emulation should be skipped and the fault should be injected.
Skipping instruction should report a failure in this case.

Signed-off-by: Nadav Amit <nadav.amit@xxxxxxxxx>
---
arch/x86/kvm/emulate.c |    5 +++++
arch/x86/kvm/x86.c     |    8 ++++++++
2 files changed, 13 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 05a562b..9a07dcd 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -3869,6 +3869,11 @@ done:
	if (ctxt->memopp && ctxt->memopp->type == OP_MEM && ctxt->rip_relative)
		ctxt->memopp->addr.mem.ea += ctxt->_eip;

+	if (rc == X86EMUL_PROPAGATE_FAULT) {
+		ctxt->have_exception = true;
+		return EMULATION_OK;
+	}
+
	return (rc != X86EMUL_CONTINUE) ? EMULATION_FAILED : EMULATION_OK;
}

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 1171def..05fd3d7 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4443,10 +4443,17 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu,
	}

	if (emulation_type & EMULTYPE_SKIP) {
+		if (ctxt->have_exception)
+			return EMULATE_FAIL;
		kvm_rip_write(vcpu, ctxt->_eip);
		return EMULATE_DONE;
	}

+	if (ctxt->have_exception) {
+		writeback = false;
+		goto post;
+	}
+
	if (retry_instruction(ctxt, cr2, emulation_type))
		return EMULATE_DONE;

@@ -4470,6 +4477,7 @@ restart:
		return handle_emulation_failure(vcpu);
	}

+post:
	if (ctxt->have_exception) {
		inject_emulated_exception(vcpu);
		r = EMULATE_DONE;
-- 
1.7.4.1


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