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

[Thomas Garnier]

On Mon, May 8, 2017 at 6:53 AM, Daniel Gruss
<daniel.gruss@xxxxxxxxxxxxxx> wrote:
> On 06.05.2017 10:38, Daniel Gruss wrote:
>>
>> On 2017-05-06 06:02, David Gens wrote:
>>>
>>> Assuming that their patch indeed leaks per-cpu addresses.. it might not
>>> necessarily
>>> be required to change it.
>>
>>
>> I think we're not leaking them (unless we still have some bug in our
>> code).
>
>
> Just to correct my answer here as well: Although we experimented with fixed
> mappings for per-cpu addresses, the current patch does not incorporate this
> yet, so it indeed still leaks. However, it is not a severe problem. The
> mapping of the required (per-cpu) variables would be at a fixed location in
> the user CR3, instead of the ones that are used in the kernel.

Why do you think it should be at a fixed location in the user CR3? I
see that you just mirror the entries. You also mirror
__entry_text_start / __entry_text_end which is part of the binary so
will leak the base address of the kernel. Maybe I am missing
something.

-- 
Thomas