From: Sean Christopherson <sean.j.christopherson@intel.com>
To: "Paolo Bonzini" <pbonzini@redhat.com>,
"Radim Krčmář" <rkrcmar@redhat.com>
Cc: Sean Christopherson <sean.j.christopherson@intel.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
Nadav Amit <nadav.amit@gmail.com>,
Andy Lutomirski <luto@kernel.org>
Subject: [PATCH] KVM: x86: Don't update RIP or do single-step on faulting emulation
Date: Fri, 23 Aug 2019 13:55:44 -0700 [thread overview]
Message-ID: <20190823205544.24052-1-sean.j.christopherson@intel.com> (raw)
Don't advance RIP or inject a single-step #DB if emulation signals a
fault. This logic applies to all state updates that are conditional on
clean retirement of the emulation instruction, e.g. updating RFLAGS was
previously handled by commit 38827dbd3fb85 ("KVM: x86: Do not update
EFLAGS on faulting emulation").
Not advancing RIP is likely a nop, i.e. ctxt->eip isn't updated with
ctxt->_eip until emulation "retires" anyways. Skipping #DB injection
fixes a bug reported by Andy Lutomirski where a #UD on SYSCALL due to
invalid state with RFLAGS.RF=1 would loop indefinitely due to emulation
overwriting the #UD with #DB and thus restarting the bad SYSCALL over
and over.
Cc: Nadav Amit <nadav.amit@gmail.com>
Cc: stable@vger.kernel.org
Reported-by: Andy Lutomirski <luto@kernel.org>
Fixes: 663f4c61b803 ("KVM: x86: handle singlestep during emulation")
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
Note, this has minor conflict with my recent series to cleanup the
emulator return flows[*]. The end result should look something like:
if (!ctxt->have_exception ||
exception_type(ctxt->exception.vector) == EXCPT_TRAP) {
kvm_rip_write(vcpu, ctxt->eip);
if (r && ctxt->tf)
r = kvm_vcpu_do_singlestep(vcpu);
__kvm_set_rflags(vcpu, ctxt->eflags);
}
[*] https://lkml.kernel.org/r/20190823010709.24879-1-sean.j.christopherson@intel.com
arch/x86/kvm/x86.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index b4cfd786d0b6..d2962671c3d3 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6611,12 +6611,13 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu,
unsigned long rflags = kvm_x86_ops->get_rflags(vcpu);
toggle_interruptibility(vcpu, ctxt->interruptibility);
vcpu->arch.emulate_regs_need_sync_to_vcpu = false;
- kvm_rip_write(vcpu, ctxt->eip);
- if (r == EMULATE_DONE && ctxt->tf)
- kvm_vcpu_do_singlestep(vcpu, &r);
if (!ctxt->have_exception ||
- exception_type(ctxt->exception.vector) == EXCPT_TRAP)
+ exception_type(ctxt->exception.vector) == EXCPT_TRAP) {
+ kvm_rip_write(vcpu, ctxt->eip);
+ if (r == EMULATE_DONE && ctxt->tf)
+ kvm_vcpu_do_singlestep(vcpu, &r);
__kvm_set_rflags(vcpu, ctxt->eflags);
+ }
/*
* For STI, interrupts are shadowed; so KVM_REQ_EVENT will
--
2.22.0
next reply other threads:[~2019-08-23 20:55 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-23 20:55 Sean Christopherson [this message]
2019-08-23 21:42 ` [PATCH] KVM: x86: Don't update RIP or do single-step on faulting emulation Nadav Amit
2019-08-23 22:46 ` Andy Lutomirski
2019-08-26 14:06 ` Sean Christopherson
2019-08-27 18:35 ` Radim Krčmář
2019-08-27 19:12 ` Jim Mattson
2019-08-27 19:49 ` Sean Christopherson
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