linux-kernel - Re: [RFC PATCH v0 00/19] x86/insn: Add an insn

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Date:   Wed, 25 Nov 2020 17:03:10 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Andy Lutomirski <luto@...capital.net>, X86 ML <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v0 00/19] x86/insn: Add an insn_decode() API

On Tue, 24 Nov 2020 18:46:47 +0100
Borislav Petkov <bp@...en8.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.

Yes, currently the buf_size is only for checking the maximum length of
the buffer, because we expect the user doesn't know the actual length of
the instruction before calling insn_get_length().
But yes, for the insn_sanity.c, the return length should be compared.

Thank you,

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


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