Re: [GIT PULL] x86/kaslr for v3.14

From: Kees Cook
Date: Tue Jan 21 2014 - 13:37:09 EST

On Tue, Jan 21, 2014 at 6:20 AM, H. Peter Anvin <hpa@xxxxxxxxx> wrote:
> On 01/21/2014 01:00 AM, Peter Zijlstra wrote:
>>> So this is presumably something that needs to be fixed in perf?
>> Where do we learn about the offset from userspace?
> Now this is tricky... if this offset is too easy to get it completely
> defeats kASLR. On the other hand, I presume that if we are exporting
> /proc/kcore we're not secure anyway. Kees, I assume that in "secure"
> mode perf annotations simply wouldn't work anyway?

The goal scope of the kernel base address randomization is to keep it
secret from non-root users, confined processes, and/or remote systems.
For local secrecy, if you're running with kaslr and you haven't set
kptr_restrict, dmesg_restrict, and perf_event_paranoid, that's a
problem since you're likely leaking things trivially through
/proc/kallsyms, dmesg, and/or perf.


Kees Cook
Chrome OS Security
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