linux-kernel - Re: [RFCv2] arm64: support HAVE_ARCH_RARE_WRITE and HAVE_ARCH_RARE_WRITE

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Message-ID: <20170330194528.GJ7909@n2100.armlinux.org.uk>
Date:   Thu, 30 Mar 2017 20:45:28 +0100
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     Kees Cook <keescook@...omium.org>
Cc:     Hoeun Ryu <hoeun.ryu@...il.com>,
        "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>,
        Andy Lutomirski <luto@...nel.org>,
        PaX Team <pageexec@...email.hu>,
        Emese Revfy <re.emese@...il.com>,
        "x86@...nel.org" <x86@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Christoffer Dall <christoffer.dall@...aro.org>,
        Mark Rutland <mark.rutland@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Laura Abbott <labbott@...hat.com>,
        Hugh Dickins <hughd@...gle.com>,
        Steve Capper <steve.capper@....com>,
        Ganapatrao Kulkarni <gkulkarni@...iumnetworks.com>,
        James Morse <james.morse@....com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFCv2] arm64: support HAVE_ARCH_RARE_WRITE and
 HAVE_ARCH_RARE_WRITE_MEMCPY

On Thu, Mar 30, 2017 at 12:38:15PM -0700, Kees Cook wrote:
> Great work! I think this will need some further changes, though, since
> it doesn't look to me like this would pass LKDTM's tests if it was
> built as a module. (This is missing from my ARM attempt too... I
> haven't figured out how to set the domain on the kernel modules...)

You're not going to be able to do it very easily.  The only way I can
think of achieving it would be to split the module area into one
chunk for text, one chunk for write-rare and one chunk for data.

I still think that using domains is a mistake for this - it's a good
solution for things that are contiguous and big (like userspace), but
not for small amounts of data (like module sections.)

-- 
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