Re: [PATCH 1/2] security: Change name of CONFIG_DEBUG_RODATA

From: Kees Cook <keescook@chromium.org>
To: Mark Rutland <mark.rutland@arm.com>,
	Michael Ellerman <mpe@ellerman.id.au>
Cc: Laura Abbott <labbott@redhat.com>,
	Jason Wessel <jason.wessel@windriver.com>,
	Jonathan Corbet <corbet@lwn.net>,
	Russell King <linux@armlinux.org.uk>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will.deacon@arm.com>,
	"James E.J. Bottomley" <jejb@parisc-linux.org>,
	Helge Deller <deller@gmx.de>,
	Martin Schwidefsky <schwidefsky@de.ibm.com>,
	Heiko Carstens <heiko.carstens@de.ibm.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
	"x86@kernel.org" <x86@kernel.org>, Rob Herring <robh@kernel.org>,
	"Rafael J. Wysocki" <rjw@rjwysocki.net>,
	Len Brown <len.brown@intel.com>, Pavel Machek <pavel@ucw.cz>,
	Jessica Yu <jeyu@redhat.com>,
	"linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	"linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>,
	linux-parisc <linux-parisc@vger.kernel.org>,
	"linux-s390@vger.kernel.org" <linux-s390@vger.kernel.org>,
	Linux PM list <linux-pm@vger.kernel.org>,
	"kernel-hardening@lists.openwall.com" 
	<kernel-hardening@lists.openwall.com>
Subject: Re: [PATCH 1/2] security: Change name of CONFIG_DEBUG_RODATA
Date: Thu, 19 Jan 2017 14:00:57 -0800	[thread overview]
Message-ID: <CAGXu5jJRrsvRAvD99O=0teqMFn9Z2rwbm=K794cD5yXKg0OL8g@mail.gmail.com> (raw)
In-Reply-To: <20170119105646.GA11176@leverpostej>

On Thu, Jan 19, 2017 at 2:56 AM, Mark Rutland <mark.rutland@arm.com> wrote:
> Hi Laura,
>
> On Wed, Jan 18, 2017 at 05:29:05PM -0800, Laura Abbott wrote:
>> diff --git a/security/Kconfig b/security/Kconfig
>> index 118f454..ad6ce82 100644
>> --- a/security/Kconfig
>> +++ b/security/Kconfig
>> @@ -158,6 +158,22 @@ config HARDENED_USERCOPY_PAGESPAN
>>         been removed. This config is intended to be used only while
>>         trying to find such users.
>>
>> +config ARCH_HAS_HARDENED_MAPPINGS
>> +     def_bool n
>> +
>> +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.

Oh, I totally missed this. Yes, we need it to stay mandatory. It
should be possible by just adding "select HARDENED_PAGE_MAPPINGS" to
the arch Kconfig, yes?

> 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.

(Adding mpe to CC...) Michael, what's needed to get this working on powerpc too?

-Kees

-- 
Kees Cook
Nexus Security