Commit 5cc244a2 authored Jan 21, 2019 by Alexander Popov Committed by Paolo Bonzini Jan 25, 2019

KVM: x86: Fix single-step debugging



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: Alexander Popov <alex.popov@linux.com>
Cc: stable@vger.kernel.org
Fixes: c8401dda ("KVM: x86: fix singlestepping over syscall")
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

parent 9699f970

arch/x86/kvm/x86.c

+1 −2

Original line number	Diff line number	Diff line
		@@ -6480,8 +6480,7 @@ restart:
		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)

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