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...
The alarm signal from the ones that don't stick is, in my opinion, the primary benefit from this work -- it makes certain classes of attack much less economical. A crash dump from a panic'd machine may include enough information to diagnose the exploited vulnerability - and once diagnosed and fixed, knowledge about the vulnerability is much less valuable. > > 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. -- 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/
