linux-kernel - Re: [PATCH 1/3] KVM: x86: fix wrong return code

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Date:   Tue, 27 Aug 2019 06:42:02 -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 1/3] KVM: x86: fix wrong return code

On Tue, Aug 27, 2019 at 01:07:04PM +0000, Jan Dakinevich wrote:
> x86_emulate_instruction(), the caller of x86_decode_insn(), expects
> that x86_decode_insn()'s returning value belongs to EMULATION_* name
> space. However, this function may return value from X86EMUL_* name
> space.
> 
> Although, the code behaves properly (because both X86EMUL_CONTINUE and
> EMULATION_OK are equal to 0) this change makes code more consistent and
> it is required for further fixes.
> 
> 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, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index 718f7d9..6170ddf 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -5144,7 +5144,7 @@ int x86_decode_insn(struct x86_emulate_ctxt *ctxt, void *insn, int insn_len)
>  	else {
>  		rc = __do_insn_fetch_bytes(ctxt, 1);
>  		if (rc != X86EMUL_CONTINUE)
> -			return rc;
> +			goto done;

Funny how things go unnoticed for years and then suddenly...

https://lkml.kernel.org/r/9bf79098-703c-e82b-7e7d-1c0a6a1023c2@redhat.com

>  	}
>  
>  	switch (mode) {
> -- 
> 2.1.4
>