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Message-ID: <20160826172414.GE15779@e104818-lin.cambridge.arm.com>
Date: Fri, 26 Aug 2016 18:24:15 +0100
From: Catalin Marinas <catalin.marinas@....com>
To: David Brown <david.brown@...aro.org>
Cc: kernel-hardening@...ts.openwall.com, James Morse <james.morse@....com>,
Julien Grall <julien.grall@....com>,
Will Deacon <will.deacon@....com>,
Kees Cook <keescook@...omium.org>,
linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 0/7] arm64: Privileged Access Never
using TTBR0_EL1 switching
On Fri, Aug 26, 2016 at 11:39:04AM -0400, David Brown wrote:
> On Fri, Aug 12, 2016 at 04:27:39PM +0100, Catalin Marinas wrote:
> >This is the first (public) attempt at emulating PAN by disabling
> >TTBR0_EL1 accesses on arm64. I chose to use a per-CPU saved_ttbr0_el1
> >variable to store the actual TTBR0 as, IMO, it looks better w.r.t. the
> >context switching code, to the detriment of a slightly more complex
> >uaccess_enable() implementation. The alternative was storing the saved
> >TTBR0 in thread_info but with more complex thread switching since TTBR0
> >is normally tied to switch_mm() rather than switch_to(). The latter may
> >also get more complicated if we are to decouple the kernel stack from
> >thread_info at some point (vmalloc'ed stacks).
> >
> >The code requires more testing, especially for combinations where UAO is
> >present but PAN is not.
>
> I briefly tried to run these patches on my HiKey board and I get a
> panic on boot. Unfortunately, I've had to head off to the Linux
> Security Summit, so I haven't been able to try to figure out what is
> going on (and I don't seem to be able to even get a capture of the log
> output). But I ran into Mark Rutland who convinced me to at least
> state the failure on the list here.
Thanks for trying to test this series. Without more information, I can't
really say where the problem is or why it fails that early (in theory it
should only affect user space). Is it with recent/latest mainline?
defconfig? Anyway, I'll wait until you get back from the conference,
maybe you get some early console output.
--
Catalin
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