Messages in this thread | | | Subject | Re: [kernel-hardening] [RFC, PATCH] x86_64: KAISER - do not map kernel in user mode | From | Daniel Gruss <> | Date | Fri, 5 May 2017 10:23:50 +0200 |
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On 04.05.2017 17:28, Thomas Garnier wrote: > Please read the documentation on submitting patches [1] and coding style [2].
I will have a closer look at that.
> - 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).
These parts are moved to a different section (.user_mapped) which is at a possibly predictable location - the location of the randomized parts of the kernel is independent of the location of .user_mapped. The code/data footprint for .user_mapped is quite small, helping to reduce or eliminate the attack surface...
> You also need to make it clear that btb attacks are still possible.
By just increasing the KASLR randomization range, btb attacks can be mitigated (for free).
> - What is the perf impact?
It will vary for different machines. We have promising results (<1%) for an i7-6700K with representative benchmarks. However, for older systems or for workloads with a lot of pressure on some TLB levels, the performance may be much worse.
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