kernel-hardening - Re: [PATCH 0/2] introduce post-init read-only memory

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Message-ID: <20151129153918.GA12215@gmail.com>
Date: Sun, 29 Nov 2015 16:39:18 +0100
From: Ingo Molnar <mingo@...nel.org>
To: PaX Team <pageexec@...email.hu>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
	kernel-hardening@...ts.openwall.com,
	Mathias Krause <minipli@...glemail.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Kees Cook <keescook@...omium.org>,
	Andy Lutomirski <luto@...capital.net>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, x86-ml <x86@...nel.org>,
	Arnd Bergmann <arnd@...db.de>,
	Michael Ellerman <mpe@...erman.id.au>, linux-arch@...r.kernel.org,
	Emese Revfy <re.emese@...il.com>
Subject: Re: [PATCH 0/2] introduce post-init read-only
 memory


* PaX Team <pageexec@...email.hu> wrote:

> On 29 Nov 2015 at 9:08, Ingo Molnar wrote:
> 
> > 
> > * PaX Team <pageexec@...email.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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