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Commit 6d3dabbd authored by Alexander Popov's avatar Alexander Popov Committed by Greg Kroah-Hartman
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KVM: x86: Fix single-step debugging 



commit 5cc244a20b86090c087073c124284381cdf47234 upstream.

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 on Jun 7, 2017 the
commit c8401dda ("KVM: x86: fix singlestepping over syscall")
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.

Signed-off-by: default avatarAlexander Popov <alex.popov@linux.com>
Cc: stable@vger.kernel.org
Fixes: c8401dda ("KVM: x86: fix singlestepping over syscall")
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent c1bfae34

arch/x86/kvm/x86.c

+1 −2
Original line number Original line Diff line number Diff line
@@ -6277,8 +6277,7 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu, 
		toggle_interruptibility(vcpu, ctxt->interruptibility);

		toggle_interruptibility(vcpu, ctxt->interruptibility);

		vcpu->arch.emulate_regs_need_sync_to_vcpu = false;

		vcpu->arch.emulate_regs_need_sync_to_vcpu = false;

		kvm_rip_write(vcpu, ctxt->eip);

		kvm_rip_write(vcpu, ctxt->eip);

		if (r == EMULATE_DONE &&

		if (r == EMULATE_DONE && ctxt->tf)

		    (ctxt->tf || (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP)))

			kvm_vcpu_do_singlestep(vcpu, &r);

			kvm_vcpu_do_singlestep(vcpu, &r);

		if (!ctxt->have_exception ||

		if (!ctxt->have_exception ||

		    exception_type(ctxt->exception.vector) == EXCPT_TRAP)

		    exception_type(ctxt->exception.vector) == EXCPT_TRAP)