Date: Sun, 29 Nov 2015 16:39:18 +0100
From: Ingo Molnar <mingo@kernel.org>
To: PaX Team <pageexec@freemail.hu>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        kernel-hardening@lists.openwall.com,
        Mathias Krause <minipli@googlemail.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Kees Cook <keescook@chromium.org>,
        Andy Lutomirski <luto@amacapital.net>, Ingo Molnar <mingo@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>, "H. Peter Anvin" <hpa@zytor.com>,
        x86-ml <x86@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
        Michael Ellerman <mpe@ellerman.id.au>, linux-arch@vger.kernel.org,
        Emese Revfy <re.emese@gmail.com>
Subject: Re: [kernel-hardening] [PATCH 0/2] introduce post-init read-only
 memory
Message-ID: <20151129153918.GA12215@gmail.com>
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* PaX Team <pageexec@freemail.hu> wrote:

> On 29 Nov 2015 at 9:08, Ingo Molnar wrote:
> 
> > 
> > * PaX Team <pageexec@freemail.hu> wrote:
> > 
> > > i don't see the compile time vs. runtime detection as 'competing' approaches, 
> > > both have their own role. [...]
> > 
> > That's true - but only as long as 'this can be solved in tooling!' is not used as 
> > an excuse to oppose the runtime solution and we end up doing neither.
> 
> actually, i already voiced my opinion elsewhere in the constify thread on the 
> kernel hardening list that adding/using __read_only is somewhat premature 
> without also adding the compile time verification part (as part of the constify 
> plugin for example). right now its use on the embedded vdso image is simple and 
> easy to verify but once people begin to add it to variables that the compiler 
> knows and cares about (say, the ops structures) then things can become fragile 
> without compile checking. so yes, i'd also advise to get such tooling in 
> *before* more __read_only usage is added.

I think you are mistaken there: if we add the page fault fixup to make sure we 
don't crash if a read-only variable is accessed, then we'll have most of the 
benefits of read-only mappings and no fragility - without having to wait for 
tooling.

Thanks,

	Ingo
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