Re: [PATCH] x86: remove arbitrary instruction size limit in instruction decoder

From: Dave Hansen
Date: Mon Nov 17 2014 - 15:49:55 EST

On 11/13/2014 06:49 AM, Masami Hiramatsu wrote:
> (2014/11/13 7:53), Dave Hansen wrote:
>> The kprobes code probably needs to be looked at here a bit more
>> carefully. This patch still respects the MAX_INSN_SIZE limit
>> there but the kprobes code does look like it might be able to
>> be a bit more strict than it currently is.
> Would you mean kprobes can copy shorter? Maybe, but I think current
> one is enough because it is on a cold path.
> OK, at least this looks good to me.

As it stands now, if you happened to be decoding an instruction which is
short and it was *JUST* before a memory hole, I think it could oops the

This doesn't look like it is very common (or maybe even possible) in

>> Note: the v10 version of the MPX patches I just posted depends
>> on this patch.
> BTW, current insn decoder doesn't support MPX... That should be
> updated (add bnd* to x86-insn-map.txt)

I think they're in there already:

> grep -i bnd arch/x86/lib/x86-opcode-map.txt
1a: BNDCL Ev,Gv | BNDCU Ev,Gv | BNDMOV Gv,Ev | BNDLDX Gv,Ev,Gv

Or were there others you were thinking of?
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at