linux-kernel - Re: [PATCH v2] tile: handle __ro_after

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Message-Id: <20161115074152.GA3929@osiris>
Date:   Tue, 15 Nov 2016 08:41:52 +0100
From:   Heiko Carstens <heiko.carstens@...ibm.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Chris Metcalf <cmetcalf@...lanox.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] tile: handle __ro_after_init like parisc does

On Mon, Nov 14, 2016 at 01:12:05PM -0800, Kees Cook wrote:
> At some point here, I want to collect all the arch maintainers and
> discuss the options for correctly reflecting the three data
> memory-protection needs we have:
> 
> - always read-only
> - read-only after init
> - read-only except during rare updates
> 
> (The latter one doesn't exist all yet...)
> 
> x86, arm, and arm64 use mark_rodata_ro() after init finishes, so they
> don't technically implement "always read-only". parisc, tile, powerpc,
> others have "always read-only", but disable read-only-after-init since
> they don't use mark_rodata_ro(). I think s390 has recently implemented
> both, but I have to double-check...

Yes, s390 has both: an early always read-only support, which is effective
as soon as paging_init() has set up and enabled page tables.
Our mark_rodata_ro() implementation only makes the ro_after_init section
read-only.