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Message-ID: <565595F5.32536.DB9FE75@pageexec.freemail.hu>
Date: Wed, 25 Nov 2015 12:05:25 +0100
From: "PaX Team" <pageexec@...email.hu>
To: kernel-hardening@...ts.openwall.com,
Mathias Krause <minipli@...glemail.com>
CC: "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
On 25 Nov 2015 at 10:13, Mathias Krause wrote:
> I myself had some educating experience seeing my machine triple fault
> when resuming from a S3 sleep. The root cause was a variable that was
> annotated __read_only but that was (unnecessarily) modified during CPU
> bring-up phase. Debugging that kind of problems is sort of a PITA, you
> could imagine.
actually the kernel could silently recover from this given how the
page fault handler could easily determine that the fault address fell
into the data..read_only section and just silently undo the read-only
property, log the event to dmesg and retry the faulting access.
> So, prior extending the usage of the __read_only annotation some
> toolchain support is needed. Maybe a gcc plugin that'll warn/error on
> code that writes to such a variable but is not __init itself.
this is exactly what i suggested earlier in the constify thread ;).
note that this will produce false positives because __init* annotations
are not propagated everywhere they could be.
> The initify and checker plugins from the PaX patch might be worth to
> look at for that purpose, as they're doing similar things already.
one of our plans for initify is to add the discovery and propagation
of _init* annotations as well, it'd not only fix the false positives
mentioned above but also help reduce the kernel size (code/data/rodata).
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