linux-kernel - Re: [PATCH v2] KVM: x86: Fix single-step debugging

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Message-ID: <845b834f-3529-056d-4373-312f7c6fc794@linux.com>
Date:   Thu, 24 Jan 2019 11:41:22 +0300
From:   Alexander Popov <alex.popov@...ux.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krcmar <rkrcmar@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Nadav Amit <nadav.amit@...il.com>,
        Andy Lutomirski <luto@...nel.org>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        H Peter Anvin <hpa@...or.com>, x86@...nel.org,
        kvm@...r.kernel.org, kernel-hardening@...ts.openwall.com,
        linux-kernel@...r.kernel.org
Cc:     Greg KH <gregkh@...uxfoundation.org>
Subject: Re: [PATCH v2] KVM: x86: Fix single-step debugging

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