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

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


-- 
Andy Lutomirski
AMA Capital Management, LLC