linux-kernel - Re: [PATCH 2/3] KVM: x86: set ctxt->have_exception in x86_decode

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Date:   Wed, 28 Aug 2019 10:19:30 +0000
From:   Jan Dakinevich <jan.dakinevich@...tuozzo.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Denis Lunev <den@...tuozzo.com>,
        Roman Kagan <rkagan@...tuozzo.com>,
        Denis Plotnikov <dplotnikov@...tuozzo.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>
Subject: Re: [PATCH 2/3] KVM: x86: set ctxt->have_exception in
 x86_decode_insn()

On Tue, 27 Aug 2019 07:53:58 -0700
Sean Christopherson <sean.j.christopherson@...el.com> wrote:

> On Tue, Aug 27, 2019 at 01:07:08PM +0000, Jan Dakinevich wrote:
> > x86_emulate_instruction() takes into account ctxt->have_exception flag
> > during instruction decoding, but in practice this flag is never set in
> > x86_decode_insn().
> > 
> > Fixes: 6ea6e84 ("KVM: x86: inject exceptions produced by x86_decode_insn")
> > Cc: Denis Lunev <den@...tuozzo.com>
> > Cc: Roman Kagan <rkagan@...tuozzo.com>
> > Cc: Denis Plotnikov <dplotnikov@...tuozzo.com>
> > Signed-off-by: Jan Dakinevich <jan.dakinevich@...tuozzo.com>
> > ---
> >  arch/x86/kvm/emulate.c | 2 ++
> >  1 file changed, 2 insertions(+)
> > 
> > diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> > index 6170ddf..f93880f 100644
> > --- a/arch/x86/kvm/emulate.c
> > +++ b/arch/x86/kvm/emulate.c
> > @@ -5395,6 +5395,8 @@ int x86_decode_insn(struct x86_emulate_ctxt *ctxt, void *insn, int insn_len)
> >  					ctxt->memopp->addr.mem.ea + ctxt->_eip);
> >  
> >  done:
> > +	if (rc == X86EMUL_PROPAGATE_FAULT)
> > +		ctxt->have_exception = true;
> 
> We should add a sanity check or two on the vector since the emulator code
> goes all over the place, e.g. #UD should not be injected/propagated, and
> trap-like exceptions should not be handled/encountered during decode.
> Note, exception_type() also warns on illegal vectors.
> 
>   WARN_ON_ONCE(ctxt->exception.vector == UD_VECTOR ||
> 	       exception_type(ctxt->exception.vector) == EXCPT_TRAP);

Ok.

> 
> >  	return (rc != X86EMUL_CONTINUE) ? EMULATION_FAILED : EMULATION_OK;
> >  }
> >  
> > -- 
> > 2.1.4
> > 


-- 
Best regards
Jan Dakinevich