linux-kernel - Re: [kernel-hardening] [PATCH v4 0/8] introduce post-init read-only memory

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Date:	Sat, 23 Jan 2016 10:49:15 +0100
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Kees Cook <keescook@...omium.org>
Cc:	Laura Abbott <laura@...bott.name>,
	"kernel-hardening@...ts.openwall.com" 
	<kernel-hardening@...ts.openwall.com>,
	Ingo Molnar <mingo@...hat.com>,
	Andy Lutomirski <luto@...capital.net>,
	"H. Peter Anvin" <hpa@...or.com>,
	Michael Ellerman <mpe@...erman.id.au>,
	Mathias Krause <minipli@...glemail.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>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-arch <linux-arch@...r.kernel.org>
Subject: Re: [kernel-hardening] [PATCH v4 0/8] introduce post-init read-only memory

Hi Kees,

On Fri, Jan 22, 2016 at 8:57 PM, Kees Cook <keescook@...omium.org> wrote:
> On Fri, Jan 22, 2016 at 11:16 AM, Laura Abbott <laura@...bott.name> wrote:
>> Kees had previously pushed a patch to do so but it exposed a couple of
>> underlying issues, mostly with low power paths
>> (c.f. http://article.gmane.org/gmane.linux.ports.arm.kernel/471199,
>> http://article.gmane.org/gmane.linux.kernel.mm/143489)
>> Those will need to be all fixed up before this could be made default.

I'm working on fixing that...

BTW, making the sections read-only is done quite late in the kernel startup
process, which means it doesn't trigger for the writes to the text segment in
secondary CPU bringup, but only for suspend/resume.

> Yeah, I've got a patch waiting to reorganize CONFIG_ARM_KERNMEM_PERMS
> to look more like arm64 (and x86) and get the feature correctly under
> CONFIG_DEBUG_RODATA. I made it default=y on v7+. rmk asked me to wait
> until -rc1 before resubmitting it.
>
> http://git.kernel.org/cgit/linux/kernel/git/kees/linux.git/commit/?h=kspp/arm-rodata&id=08bebfd2e7fb8a9f364ced74c356642d64e1f43e

One other concern is indeed memory usage ("ALIGN(1<<SECTION_SHIFT)"?).
Enabling CONFIG_ARM_KERNMEM_PERMS and CONFIG_DEBUG_RODATA in my test kernel
configs make the kernel too big to boot (overwritten DTB?) for 3 out of 4 arm
shmobile targets...

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds