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

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Date:   Mon, 21 Jan 2019 15:24:27 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Alexander Popov <alex.popov@...ux.com>
Cc:     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
Subject: Re: [PATCH v2] KVM: x86: Fix single-step debugging

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@...ux.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>