linux-kernel - Re: [PATCH v2 1/4] init: create cmdline param to disable readonly

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Message-ID: <20151201072403.GA28270@gmail.com>
Date:	Tue, 1 Dec 2015 08:24:03 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Kees Cook <keescook@...omium.org>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Michael Ellerman <mpe@...erman.id.au>,
	"James E.J. Bottomley" <jejb@...isc-linux.org>,
	Catalin Marinas <catalin.marinas@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	Andy Lutomirski <luto@...capital.net>,
	"H. Peter Anvin" <hpa@...or.com>,
	Mathias Krause <minipli@...glemail.com>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"x86@...nel.org" <x86@...nel.org>, Arnd Bergmann <arnd@...db.de>,
	PaX Team <pageexec@...email.hu>,
	Emese Revfy <re.emese@...il.com>,
	"kernel-hardening@...ts.openwall.com" 
	<kernel-hardening@...ts.openwall.com>,
	linux-arch <linux-arch@...r.kernel.org>
Subject: Re: [PATCH v2 1/4] init: create cmdline param to disable readonly


* Russell King - ARM Linux <linux@....linux.org.uk> wrote:

> On Mon, Nov 30, 2015 at 01:52:10PM -0800, Kees Cook wrote:
> > On Wed, Nov 25, 2015 at 11:51 PM, Ingo Molnar <mingo@...nel.org> wrote:
> > > * Kees Cook <keescook@...omium.org> wrote:
> > >> +#ifdef CONFIG_DEBUG_RODATA
> > >
> > > Btw., could you please remove the Kconfig option altogether in an additional patch
> > > and make read-only sections an always-on feature? It has been default-y for years
> > > and all distros have it enabled.
> > 
> > Yeah, this is something I've wanted to do for a while, but I would
> > point out that only a few architectures have actually implemented it,
> > and for arm and arm64 it was very recent:
> 
> I don't think it can entirely be a kernel command line option.  On ARM,
> enabling DEBUG_RODATA has a substantial effect on the size of the kernel
> image - we have to pad various sections to 1MB boundaries so we can
> set the appropriate permissions.
> 
> Forcing this layout on everyone won't work.

Yeah, so I'd suggest to have it always-on on x86 (after adding the boot option), 
to simplify the x86 code and to make it more obvious that we rely on this.

There's a moderate amount of #ifdeffery around this:

  triton:~/tip> git grep -w CONFIG_DEBUG_RODATA arch/x86/  | grep \# | wc -l
  15

Thanks,

	Ingo
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