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...
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/
