Re: [tip:x86/boot] x86/mm: Enable KASLR for physical mapping memory regions

[Brian Gerst <brgerst@gmail.com>]

On Fri, Jul 8, 2016 at 4:35 PM, tip-bot for Thomas Garnier
<tipbot@zytor.com> wrote:
> Commit-ID:  021182e52fe01c1f7b126f97fd6ba048dc4234fd
> Gitweb:     http://git.kernel.org/tip/021182e52fe01c1f7b126f97fd6ba048dc4234fd
> Author:     Thomas Garnier <thgarnie@google.com>
> AuthorDate: Tue, 21 Jun 2016 17:47:03 -0700
> Committer:  Ingo Molnar <mingo@kernel.org>
> CommitDate: Fri, 8 Jul 2016 17:35:15 +0200
>
> x86/mm: Enable KASLR for physical mapping memory regions
>
> Add the physical mapping in the list of randomized memory regions.
>
> The physical memory mapping holds most allocations from boot and heap
> allocators. Knowing the base address and physical memory size, an attacker
> can deduce the PDE virtual address for the vDSO memory page. This attack
> was demonstrated at CanSecWest 2016, in the following presentation:
>
>   "Getting Physical: Extreme Abuse of Intel Based Paged Systems":
>   https://github.com/n3k/CansecWest2016_Getting_Physical_Extreme_Abuse_of_Intel_Based_Paging_Systems/blob/master/Presentation/CanSec2016_Presentation.pdf
>
> (See second part of the presentation).
>
> The exploits used against Linux worked successfully against 4.6+ but
> fail with KASLR memory enabled:
>
>   https://github.com/n3k/CansecWest2016_Getting_Physical_Extreme_Abuse_of_Intel_Based_Paging_Systems/tree/master/Demos/Linux/exploits
>
> Similar research was done at Google leading to this patch proposal.
>
> Variants exists to overwrite /proc or /sys objects ACLs leading to
> elevation of privileges. These variants were tested against 4.6+.
>
> The page offset used by the compressed kernel retains the static value
> since it is not yet randomized during this boot stage.

This patch is causing my system to fail to boot.  The last messages
that are printed before it hangs are:

[    0.195652] smpboot: CPU0: AMD Phenom(tm) II X6 1055T Processor
(family: 0x10, model: 0xa, stepping: 0x0)
[    0.195656] Performance Events: AMD PMU driver.
[    0.195659] ... version:                0
[    0.195660] ... bit width:              48
[    0.195660] ... generic registers:      4
[    0.195661] ... value mask:             0000ffffffffffff
[    0.195662] ... max period:             00007fffffffffff
[    0.195663] ... fixed-purpose events:   0
[    0.195664] ... event mask:             000000000000000f
[    0.196185] NMI watchdog: enabled on all CPUs, permanently consumes
one hw-PMU counter.
[    0.196291] x86: Booting SMP configuration:
[    0.196292] .... node  #0, CPUs:      #1

I'm taking a guess here, but it may be that this is interfering with
the APIC accesses.

--
Brian Gerst