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Date:   Sun, 29 Nov 2020 17:50:05 +0900
From:   Masami Hiramatsu <mhiramat@kernel.org>
To:     Andy Lutomirski <luto@amacapital.net>
Cc:     Borislav Petkov <bp@alien8.de>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        X86 ML <x86@kernel.org>, LKML <linux-kernel@vger.kernel.org>
Subject: Re: [RFC PATCH v0 00/19] x86/insn: Add an insn_decode() API
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On Fri, 27 Nov 2020 09:45:39 -0800
Andy Lutomirski <luto@amacapital.net> wrote:

> On Tue, Nov 24, 2020 at 9:46 AM Borislav Petkov <bp@alien8.de> wrote:
> >
> > On Tue, Nov 24, 2020 at 11:19:33AM +0100, Borislav Petkov wrote:
> > > In any case, at least the case where I give it
> > >
> > > 0x48 0xcf 0x48 0x83
> > >
> > > and say that buf size is 4, should return an error because the second
> > > insn is incomplete. So I need to go look at that now.
> >
> > Ok, got it:
> >
> > ./arch/x86/tools/insn_sanity: Success: decoded and checked 10000 random instructions with 0 errors (seed:0x826fdf9c)
> > insn buffer:
> > 0x48 0xcf 0x48 0x83 0x90 0x90 0x90 0x90 0x90 0x90 0x90 0x90 0x90 0x90 0x90
> > supplied buf size: 15, ret 0
> > supplied buf size: 2, ret 0
> > supplied buf size: 3, ret 0
> > supplied buf size: 4, ret 0
> > supplied buf size: 1, ret -22
> >
> > the current decoder simply decodes the *first* insn in the buffer it
> > encounters and that's it.
> >
> > When you give it a buffer of size smaller than the first instruction:
> >
> > supplied buf size: 1, ret -22
> >
> > while the first insn is 2 bytes long:
> >
> > 0x48 0xcf (IRETQ)
> >
> > then it signals an error.
> >
> > Andy, does that work for your use cases?
> 
> Is -22 (-EINVAL) the same error it returns if you pass in garbage?
> How hard would it be to teach it to return a different error code when
> the buffer is too small?
> 

Good point. I think we can return, e.g. -EFAULT if we failed in get_next(). Then, we can read out next page, for example.

Thank you,

-- 
Masami Hiramatsu <mhiramat@kernel.org>