Messages in this thread | | | Date | Sun, 21 Jun 2015 08:55:23 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH 2/2] x86: fix incomplete clear by clear_user() |
| |
* Alexey Dobriyan <adobriyan@gmail.com> wrote:
> clear_user() used MOVQ+MOVB and if MOVQ faults, code simply exits and > honestly returns remaining length. In case of unaligned area, unaligned > remainder would count towards return value (correctly) but not cleared > (lazy code at least): > > clear_user(p + 4096 - 4, 8) = 8 > > No one would have noticed but REP MOVSB addition to clear_user() > repertoire creates a problem: REP MOVSB does everything correctly, > clears and counts to the last possible byte, but REP STOSQ and MOVQ > variants DO NOT: > > MOVQ clear_user(p + 4096 - 4, 8) = 8 > REP STOSQ clear_user(p + 4096 - 4, 8) = 8 > REP STOSB clear_user(p + 4096 - 4, 8) = 4 > > Patch fixes incomplete clear on 32-bit and 64-bit REP STOSQ, MOVQ.
So please flip the order of the changes around so that we never have this inconsistency observable: i.e. first update the existing clearing method, then move it and introduce the new variants without having to patch them.
Thanks,
Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in Please read the FAQ at http://www.tux.org/lkml/
| |