From: Paolo Bonzini <pbonzini@redhat.com>
To: Alexander Popov <alex.popov@linux.com>,
Radim Krcmar <rkrcmar@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Nadav Amit <nadav.amit@gmail.com>,
Andy Lutomirski <luto@kernel.org>,
Stefan Hajnoczi <stefanha@redhat.com>,
H Peter Anvin <hpa@zytor.com>,
x86@kernel.org, kvm@vger.kernel.org,
kernel-hardening@lists.openwall.com,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] KVM: x86: Fix single-step debugging
Date: Fri, 25 Jan 2019 18:52:15 +0100 [thread overview]
Message-ID: <2cf80ef9-cacc-c730-7a9e-301703ddc80d@redhat.com> (raw)
In-Reply-To: <1548074920-10651-1-git-send-email-alex.popov@linux.com>
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
next prev parent reply other threads:[~2019-01-25 17:52 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-21 12:48 [PATCH v2] KVM: x86: Fix single-step debugging Alexander Popov
2019-01-21 14:24 ` Greg KH
2019-01-25 17:38 ` Paolo Bonzini
2019-01-24 8:41 ` Alexander Popov
2019-01-25 17:52 ` Paolo Bonzini [this message]
2019-02-05 22:55 ` Jim Mattson
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