releases/4.4.173/kvm-x86-fix-single-step-debugging.patch

   1 From 5cc244a20b86090c087073c124284381cdf47234 Mon Sep 17 00:00:00 2001
   2 From: Alexander Popov <alex.popov@linux.com>
   3 Date: Mon, 21 Jan 2019 15:48:40 +0300
   4 Subject: KVM: x86: Fix single-step debugging
   5
   6 From: Alexander Popov <alex.popov@linux.com>
   7
   8 commit 5cc244a20b86090c087073c124284381cdf47234 upstream.
   9
  10 The single-step debugging of KVM guests on x86 is broken: if we run
  11 gdb 'stepi' command at the breakpoint when the guest interrupts are
  12 enabled, RIP always jumps to native_apic_mem_write(). Then other
  13 nasty effects follow.
  14
  15 Long investigation showed that on Jun 7, 2017 the
  16 commit c8401dda2f0a00cd25c0 ("KVM: x86: fix singlestepping over syscall")
  17 introduced the kvm_run.debug corruption: kvm_vcpu_do_singlestep() can
  18 be called without X86_EFLAGS_TF set.
  19
  20 Let's fix it. Please consider that for -stable.
  21
  22 Signed-off-by: Alexander Popov <alex.popov@linux.com>
  23 Cc: stable@vger.kernel.org
  24 Fixes: c8401dda2f0a00cd25c0 ("KVM: x86: fix singlestepping over syscall")
  25 Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
  26 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  27
  28 ---
  29  arch/x86/kvm/x86.c |    3 +--
  30  1 file changed, 1 insertion(+), 2 deletions(-)
  31
  32 --- a/arch/x86/kvm/x86.c
  33 +++ b/arch/x86/kvm/x86.c
  34 @@ -5524,8 +5524,7 @@ restart:
  35                 toggle_interruptibility(vcpu, ctxt->interruptibility);
  36                 vcpu->arch.emulate_regs_need_sync_to_vcpu = false;
  37                 kvm_rip_write(vcpu, ctxt->eip);
  38 -               if (r == EMULATE_DONE &&
  39 -                   (ctxt->tf || (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP)))
  40 +               if (r == EMULATE_DONE && ctxt->tf)
  41                         kvm_vcpu_do_singlestep(vcpu, &r);
  42                 if (!ctxt->have_exception ||
  43                     exception_type(ctxt->exception.vector) == EXCPT_TRAP)