linux-kernel - [PATCH v3 1/2] KVM: x86: always stop emulation on page fault

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Message-ID: <1567066988-23376-2-git-send-email-jan.dakinevich@virtuozzo.com>
Date:   Thu, 29 Aug 2019 08:23:18 +0000
From:   Jan Dakinevich <jan.dakinevich@...tuozzo.com>
To:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     Jan Dakinevich <jan.dakinevich@...tuozzo.com>,
        Denis Lunev <den@...tuozzo.com>,
        Roman Kagan <rkagan@...tuozzo.com>,
        Denis Plotnikov <dplotnikov@...tuozzo.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>
Subject: [PATCH v3 1/2] KVM: x86: always stop emulation on page fault

inject_emulated_exception() returns true if and only if nested page
fault happens. However, page fault can come from guest page tables
walk, either nested or not nested. In both cases we should stop an
attempt to read under RIP and give guest to step over its own page
fault handler.

Fixes: 6ea6e84 ("KVM: x86: inject exceptions produced by x86_decode_insn")
Cc: Denis Lunev <den@...tuozzo.com>
Cc: Roman Kagan <rkagan@...tuozzo.com>
Cc: Denis Plotnikov <dplotnikov@...tuozzo.com>
Signed-off-by: Jan Dakinevich <jan.dakinevich@...tuozzo.com>
---
 arch/x86/kvm/x86.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index b4cfd78..6bf7b55 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6537,8 +6537,13 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu,
 			if (reexecute_instruction(vcpu, cr2, write_fault_to_spt,
 						emulation_type))
 				return EMULATE_DONE;
-			if (ctxt->have_exception && inject_emulated_exception(vcpu))
+			if (ctxt->have_exception) {
+				WARN_ON_ONCE(ctxt->exception.vector == UD_VECTOR);
+				WARN_ON_ONCE(exception_type(ctxt->exception.vector)
+					== EXCPT_TRAP);
+				inject_emulated_exception(vcpu);
 				return EMULATE_DONE;
+			}
 			if (emulation_type & EMULTYPE_SKIP)
 				return EMULATE_FAIL;
 			return handle_emulation_failure(vcpu, emulation_type);
-- 
2.1.4