On Thu, Apr 4, 2013 at 2:01 PM, H. Peter Anvin <h...@zytor.com> wrote: > What system monitoring? Most systems don't have much...
The security of an unmonitored system is going to be much lower than of a well-monitored system. That's true independent of whether kASLR is deployed. > > Kees Cook <keesc...@chromium.org> wrote: > >>On Thu, Apr 4, 2013 at 1:58 PM, H. Peter Anvin <h...@zytor.com> wrote: >>> It seems to me that you are assuming that the attacker is targeting a >>specific system, but a bot might as well target 256 different systems >>and see what sticks... >> >>Certainly, but system monitoring will show 255 crashed machines, which >>is a huge blip on any radar. :) >> >>-Kees >> >>> >>> Kees Cook <keesc...@chromium.org> wrote: >>> >>>>On Thu, Apr 4, 2013 at 1:12 PM, H. Peter Anvin <h...@zytor.com> wrote: >>>>> On 04/04/2013 01:07 PM, Kees Cook wrote: >>>>>> However, the benefits of >>>>>> this feature in certain environments exceed the perceived >>>>weaknesses[2]. >>>>> >>>>> Could you clarify? >>>> >>>>I would summarize the discussion of KASLR weaknesses into to two >>>>general observations: >>>>1- it depends on address location secrecy and leaks are common/easy. >>>>2- it has low entropy so attack success rates may be high. >>>> >>>>For "1", as Julien mentions, remote attacks and attacks from a >>>>significantly contained process (via seccomp-bpf) minimizes the leak >>>>exposure. For local attacks, cache timing attacks and other things >>>>also exist, but the ASLR can be improved to defend against that too. >>>>So, KASLR is useful on systems that are virtualization hosts, >>>>providing remote services, or running locally confined processes. >>>> >>>>For "2", I think that the comparison to userspace ASLR entropy isn't >>>>as direct. For userspace, most systems don't tend to have any kind of >>>>watchdog on segfaulting processes, so a remote attacker could just >>>>keep trying an attack until they got lucky, in which case low entropy >>>>is a serious problem. In the case of KASLR, a single attack failure >>>>means the system goes down, which makes mounting an attack much more >>>>difficult. I think 8 bits is fine to start with, and I think start >>>>with a base offset ASLR is a good first step. We can improve things >>in >>>>the future. >>>> >>>>-Kees >>>> >>>>-- >>>>Kees Cook >>>>Chrome OS Security >>> >>> -- >>> Sent from my mobile phone. Please excuse brevity and lack of >>formatting. >> >> >> >>-- >>Kees Cook >>Chrome OS Security > > -- > Sent from my mobile phone. Please excuse brevity and lack of formatting. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
