linux-kernel - Re: [PATCH 1/2] security: Change name of CONFIG_DEBUG

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Message-ID: <CAGXu5jJRrsvRAvD99O=0teqMFn9Z2rwbm=K794cD5yXKg0OL8g@mail.gmail.com>
Date:   Thu, 19 Jan 2017 14:00:57 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Mark Rutland <mark.rutland@....com>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     Laura Abbott <labbott@...hat.com>,
        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>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        "x86@...nel.org" <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-doc@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        linux-parisc <linux-parisc@...r.kernel.org>,
        "linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
        Linux PM list <linux-pm@...r.kernel.org>,
        "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH 1/2] security: Change name of CONFIG_DEBUG_RODATA

On Thu, Jan 19, 2017 at 2:56 AM, Mark Rutland <mark.rutland@....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