On Thu, Jan 15, 2015 at 5:02 PM, Masami Hiramatsu <[email protected]> wrote: > (2015/01/16 0:22), Andy Lutomirski wrote: >> On Jan 15, 2015 4:37 AM, "Masami Hiramatsu" >> <[email protected]> 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 <[email protected]> >>>> --- >>>> 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? > > Yes, what I meant about "15" was the the "15" in the comment. > So > > + /* > + * Instructions longer than MAX_INSN_SIZE bytes are invalid even if the > + * input buffer is long enough to hold them. > + */ > + if (buf_len > MAX_INSN_SIZE) > + buf_len = MAX_INSN_SIZE; > > is acceptable. > >> If you think the current code is okay for 3.19, I can fold the two >> patches together and send for 3.20. > > If it does really cause a bug or a real problem, it must fix asap. > If not, I'd like to fix this issue with changing MAX_INSN_SIZE to 15. >
Since this has waited for quite a while and there's no known urgent problem, I'll just send a combined patch. --Andy > Thank you, > > -- > Masami HIRAMATSU > Software Platform Research Dept. Linux Technology Research Center > Hitachi, Ltd., Yokohama Research Laboratory > E-mail: [email protected] > > -- Andy Lutomirski AMA Capital Management, LLC -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
