* [PATCH] KVM: x86: Fix single-step debugging
@ 2019-01-21 12:20 Alexander Popov
2019-01-21 12:47 ` Alexander Popov
0 siblings, 1 reply; 2+ messages in thread
From: Alexander Popov @ 2019-01-21 12:20 UTC (permalink / raw)
To: Paolo Bonzini, Radim Krcmar, Thomas Gleixner, Ingo Molnar,
Borislav Petkov, Nadav Amit, Andy Lutomirski, Stefan Hajnoczi,
H Peter Anvin, x86, kvm, kernel-hardening, linux-kernel,
Alexander Popov
The single-step debugging of KVM guests on x86 is broken: if we run
gdb 'stepi' command at the breakpoint when the guest interrupts are
enabled, RIP always jumps to native_apic_mem_write(). Then other
nasty effects follow.
Long investigation showed that the commit c8401dda2f0a00cd25c0 (Jun 7 2017)
introduced the kvm_run.debug corruption: kvm_vcpu_do_singlestep() can
be called without X86_EFLAGS_TF set.
Let's fix it. Please consider that for -stable.
---
arch/x86/kvm/x86.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index f049ecf..9686068 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6407,8 +6407,7 @@ int x86_emulate_instruction(struct kvm_vcpu *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 || (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP)))
+ if (r == EMULATE_DONE && ctxt->tf)
kvm_vcpu_do_singlestep(vcpu, &r);
if (!ctxt->have_exception ||
exception_type(ctxt->exception.vector) == EXCPT_TRAP)
--
2.7.4
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] KVM: x86: Fix single-step debugging
2019-01-21 12:20 [PATCH] KVM: x86: Fix single-step debugging Alexander Popov
@ 2019-01-21 12:47 ` Alexander Popov
0 siblings, 0 replies; 2+ messages in thread
From: Alexander Popov @ 2019-01-21 12:47 UTC (permalink / raw)
To: Paolo Bonzini, Radim Krcmar, Thomas Gleixner, Ingo Molnar,
Borislav Petkov, Nadav Amit, Andy Lutomirski, Stefan Hajnoczi,
H Peter Anvin, x86, kvm, kernel-hardening, linux-kernel
Cc: Alexander Popov
Oops. I've forgotten about checkpatch.pl.
I've fixed the commit message and will resend the patch shortly.
--
Alexander
^ permalink raw reply [flat|nested] 2+ messages in thread
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