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    SubjectRe: [RFC PATCH v0 00/19] x86/insn: Add an insn_decode() API
    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>

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