On Jan 15, 2015 4:37 AM, "Masami Hiramatsu"
<masami.hiramatsu...@hitachi.com> wrote:
>
> (2015/01/14 6:49), Andy Lutomirski wrote:
> > x86 instructions cannot exceed 15 bytes, and the instruction decoder
> > should enforce that. Prior to 6ba48ff46f76, the instruction length
> > limit was implicitly set to 16, which was an approximation of 15,
> > but there is currently no limit at all.
> >
> > Fix the decoder to reject instructions that exceed 15 bytes.
> > A subsequent patch (targetted for 3.20) will fix MAX_INSN_SIZE.
>
> Hmm, is there any problem to just change MAX_INSN_SIZE to 15?
I don't want to do that for 3.19. It's kind of late.
>
> > Other than potentially confusing some of the decoder sanity checks,
> > I'm not aware of any actual problems that omitting this check would
> > cause.
> >
> > Fixes: 6ba48ff46f76 x86: Remove arbitrary instruction size limit in
> > instruction decoder
> > Signed-off-by: Andy Lutomirski <l...@amacapital.net>
> > ---
> > arch/x86/lib/insn.c | 7 +++++++
> > 1 file changed, 7 insertions(+)
> >
> > diff --git a/arch/x86/lib/insn.c b/arch/x86/lib/insn.c
> > index 2480978b31cc..7b80745d2c5a 100644
> > --- a/arch/x86/lib/insn.c
> > +++ b/arch/x86/lib/insn.c
> > @@ -52,6 +52,13 @@
> > */
> > void insn_init(struct insn *insn, const void *kaddr, int buf_len, int
> > x86_64)
> > {
> > + /*
> > + * Instructions longer than 15 bytes are invalid even if the
> > + * input buffer is long enough to hold them.
> > + */
> > + if (buf_len > 15)
> > + buf_len = 15;
> > +
>
> Without changing the MAX_INSN_SIZE, this looks very odd, since all other
> code suppose that the max length of an instruction is 16 (MAX_INSN_SIZE)
> except here.
I thought this was your suggestion. Did I misunderstand?
If you think the current code is okay for 3.19, I can fold the two
patches together and send for 3.20.
--Andy
>
> Thank you,
>
> > memset(insn, 0, sizeof(*insn));
> > insn->kaddr = kaddr;
> > insn->end_kaddr = kaddr + buf_len;
> >
>
>
> --
> Masami HIRAMATSU
> Software Platform Research Dept. Linux Technology Research Center
> Hitachi, Ltd., Yokohama Research Laboratory
> E-mail: masami.hiramatsu...@hitachi.com
>
>
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