linux-kernel - Re: [RFC] Have insn decoder functions return success/failure

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Date:   Wed, 21 Oct 2020 23:26:13 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     x86-ml <x86@...nel.org>, Joerg Roedel <jroedel@...e.de>,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] Have insn decoder functions return success/failure

On Wed, 21 Oct 2020 11:27:50 +0200
Borislav Petkov <bp@...en8.de> wrote:

> On Wed, Oct 21, 2020 at 09:50:13AM +0900, Masami Hiramatsu wrote:
> > Agreed. So I'm OK for returning the result of "decoding".
> > But we also need to note that the returning success doesn't
> > mean the instruction is valid. That needs another validator.
> >
> ...
> 
> >
> > Yes, so let's add the return value (with a note, so that someone
> > does not try to use it for validation).
> 
> Ok, I'm unclear on that "validation" you talk about. What exactly do
> you mean? Can you give an example of how one would determine whether an
> instruction is valid? And valid how?

Hmm, I meant someone might think it can be used for filtering the
instruction something like,

insn_init(insn, buf, buflen, 1);
ret = insn_get_length(insn);
if (!ret) {
	/* OK, this is safe */
	patch_text(buf, trampoline);
}

No, we need another validator for such usage.

Thank you,
 
> 
> Thx.
> 
> -- 
> Regards/Gruss,
>     Boris.
> 
> https://people.kernel.org/tglx/notes-about-netiquette


-- 
Masami Hiramatsu <mhiramat@...nel.org>