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Date: Fri, 7 Apr 2017 17:22:39 +0100
From: Mark Rutland <mark.rutland@....com>
To: Andy Lutomirski <luto@...nel.org>
Cc: Mathias Krause <minipli@...glemail.com>,
Thomas Gleixner <tglx@...utronix.de>,
Kees Cook <keescook@...omium.org>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>,
Hoeun Ryu <hoeun.ryu@...il.com>, PaX Team <pageexec@...email.hu>,
Emese Revfy <re.emese@...il.com>,
Russell King <linux@...linux.org.uk>, X86 ML <x86@...nel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>,
Peter Zijlstra <peterz@...radead.org>
Subject: Re: Re: [RFC v2][PATCH 04/11] x86: Implement
__arch_rare_write_begin/unmap()
On Fri, Apr 07, 2017 at 09:14:29AM -0700, Andy Lutomirski wrote:
> I think we're approaching this all wrong, actually. The fact that x86
> has this CR0.WP thing is arguably a historical accident, and the fact
> that PaX uses it doesn't mean that PaX is doing it the best way for
> upstream Linux.
>
> Why don't we start at the other end and do a generic non-arch-specific
> implementation: set up an mm_struct that contains an RW alias of the
> relevant parts of rodata and use use_mm to access it. (That is,
> get_fs() to back up the old fs, set_fs(USER_DS),
> use_mm(&rare_write_mm), do the write using copy_to_user, undo
> everything.)
FWIW, I completely agree with this approach.
That's largely the approach arm64 would have to take regardless (as per
Hoeun's patches), and having a consistent common implementation would be
desireable.
There are a couple of other complications to handle (e.g. a perf
interrupt coming in and trying to read from the mapping), but I think we
can handle that generically.
Thanks,
Mark.
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