Re: [kernel-hardening] [RFC, PATCH] x86_64: KAISER - do not map kernel in user mode

From: Thomas Garnier
Date: Thu May 04 2017 - 11:28:58 EST

On Thu, May 4, 2017 at 3:02 AM, Daniel Gruss
<daniel.gruss@xxxxxxxxxxxxxx> wrote:
> After several recent works [1,2,3] KASLR on x86_64 was basically considered
> dead by many researchers. We have been working on an efficient but effective
> fix for this problem and found that not mapping the kernel space when
> running in user mode is the solution to this problem [4] (the corresponding
> paper [5] will be presented at ESSoS17).
> With this RFC patch we allow anybody to configure their kernel with the flag
> CONFIG_KAISER to add our defense mechanism.
> If there are any questions we would love to answer them.
> We also appreciate any comments!
> Cheers,
> Daniel (+ the KAISER team from Graz University of Technology)
> [1]
> [2]
> [3]
> [4]
> [5]

Please read the documentation on submitting patches [1] and coding style [2].

I have two questions:

- How this approach prevent the hardware attacks you mentioned? You
still have to keep a part of _text in the pagetable and an attacker
could discover it no? (and deduce the kernel base address). You also
need to make it clear that btb attacks are still possible.
- What is the perf impact?