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Date: Wed, 25 Jan 2017 12:37:14 +0100
From: Laura Abbott <labbott@...hat.com>
To: Heiko Carstens <heiko.carstens@...ibm.com>,
Mark Rutland <mark.rutland@....com>
Cc: Kees Cook <keescook@...omium.org>,
Jason Wessel <jason.wessel@...driver.com>, Jonathan Corbet <corbet@....net>,
Russell King <linux@...linux.org.uk>,
Catalin Marinas <catalin.marinas@....com>, Will Deacon
<will.deacon@....com>, "James E.J. Bottomley" <jejb@...isc-linux.org>,
Helge Deller <deller@....de>, Martin Schwidefsky <schwidefsky@...ibm.com>,
Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
Rob Herring <robh@...nel.org>, "Rafael J. Wysocki" <rjw@...ysocki.net>,
Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
Jessica Yu <jeyu@...hat.com>, linux-doc@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
linux-parisc@...r.kernel.org, linux-s390@...r.kernel.org,
linux-pm@...r.kernel.org, kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH 1/2] security: Change name of CONFIG_DEBUG_RODATA
On 01/19/2017 12:33 PM, Heiko Carstens wrote:
> On Thu, Jan 19, 2017 at 10:56:46AM +0000, Mark Rutland wrote:
>>> +config HARDENED_PAGE_MAPPINGS
>>> + bool "Mark kernel mappings with stricter permissions (RO/W^X)"
>>> + default y
>>> + depends on ARCH_HAS_HARDENED_MAPPINGS
>>> + help
>>> + If this is set, kernel text and rodata memory will be made read-only,
>>> + and non-text memory will be made non-executable. This provides
>>> + protection against certain security attacks (e.g. executing the heap
>>> + or modifying text).
>>> +
>>> + Unless your system has known restrictions or performance issues, it
>>> + is recommended to say Y here.
>>
>> It's somewhat unfortunate that this means the feature is no longer
>> mandatory on arm64 (and s390+x86). We have a boot-time switch to turn
>> the protections off, so I was hoping we could make this mandatory on all
>> architectures with support.
>>
>> It would be good to see if we could make this mandatory for arm and
>> parisc, or if it really needs to be optional for either of those.
>
> Looks like the config option is a no-op on parisc just like it is on
> s390. Irrelavant of the config option at least on s390 the page tables for
> kernel text and rodata will be read-only anyway.
>
> This works since ages and I don't see a reason why this should be
> changed. Also trying to disable this with the "rodata=" command line option
> does not work at least on s390, and I guess this is true for parisc as
> well.
>
> The only thing implemented with CONFIG_DEBUG_RODATA on both architectures
> is to emit a message that states memory has been protected
> (mark_rodata_ro).
> This just avoids a wrong "Kernel memory protection disabled." message.
>
> So yes, I'd really like to keep this option mandatory.
>
(Apologies, my SMTP server was set up incorrectly so this didn't get
sent out when I thought it did)
Okay, that's useful to know. I think I'm going to add a
'select HARDENED_MAPPINGS' (or whatever it gets changed to) to arches
that were previously def_bool. This is a slight Kconfig semantic change
but as has been pointed out we now have the command line option.
Thanks,
Laura
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