| Message ID | 1548074920-10651-1-git-send-email-alex.popov@linux.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2] KVM: x86: Fix single-step debugging | expand |
On Mon, Jan 21, 2019 at 03:48:40PM +0300, Alexander Popov wrote: > 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 c8401dda2f0a00cd25c0 ("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> > --- > arch/x86/kvm/x86.c | 3 +-- > 1 file changed, 1 insertion(+), 2 deletions(-) <formletter> This is not the correct way to submit patches for inclusion in the stable kernel tree. Please read: https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html for how to do this properly. </formletter>
On 21.01.2019 15:48, Alexander Popov wrote: > 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 c8401dda2f0a00cd25c0 ("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. Hello everyone! Just a friendly ping about this fix. Looking forward to the feedback. Best regards, Alexander
On 21/01/19 15:24, Greg KH wrote: > On Mon, Jan 21, 2019 at 03:48:40PM +0300, Alexander Popov wrote: >> 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 c8401dda2f0a00cd25c0 ("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> >> --- >> arch/x86/kvm/x86.c | 3 +-- >> 1 file changed, 1 insertion(+), 2 deletions(-) > > <formletter> > > This is not the correct way to submit patches for inclusion in the > stable kernel tree. Please read: > https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html > for how to do this properly. > > </formletter> > Yup, will take care of doing this properly. :) Paolo
On 21/01/19 13:48, Alexander Popov wrote: > 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 c8401dda2f0a00cd25c0 ("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> > --- > 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) > Queued, with Cc to stable and the right "Fixes" trailer. Paolo
On Fri, Jan 25, 2019 at 9:52 AM Paolo Bonzini <pbonzini@redhat.com> wrote: > > On 21/01/19 13:48, Alexander Popov wrote: > > 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 c8401dda2f0a00cd25c0 ("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> > > --- > > 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) > > > > Queued, with Cc to stable and the right "Fixes" trailer. > > Paolo This patch seems to imply that userspace is expected to set the guest's RFLAGS.TF when requesting KVM_GUEST_SINGLESTEP, but the documentation for KVM_GUEST_SINGLESTEP is not clear about this. Can someone clarify how KVM_GUEST_SINGLESTEP is supposed to work?
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)
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 c8401dda2f0a00cd25c0 ("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> --- arch/x86/kvm/x86.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-)