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

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Message-ID: <20190827145358.GD27459@linux.intel.com>
Date:   Tue, 27 Aug 2019 07:53:58 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Jan Dakinevich <jan.dakinevich@...tuozzo.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, 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);

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