linux-kernel - Re: KASLR support on ARM with Kernel 4.9 and 4.14

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Message-ID: <CAOuPNLijjua222eV-6bnLyidsuY49-KuQSERUSXLpc+u+qeqLg@mail.gmail.com>
Date:   Wed, 30 Sep 2020 19:28:02 +0530
From:   Pintu Agarwal <pintu.ping@...il.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Ard Biesheuvel <ardb@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Arnd Bergmann <arnd@...db.de>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Marc Zyngier <marc.zyngier@....com>,
        Dave Martin <dave.martin@....com>,
        Kernelnewbies <kernelnewbies@...nelnewbies.org>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        open list <linux-kernel@...r.kernel.org>,
        Tony Lindgren <tony@...mide.com>, matt@...eblueprint.co.uk,
        nico@...aro.org, Thomas Garnier <thgarnie@...gle.com>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: KASLR support on ARM with Kernel 4.9 and 4.14

On Tue, 29 Sep 2020 at 01:20, Kees Cook <keescook@...omium.org> wrote:

> Note that I still can't explain what you're seeing. /proc/kallsyms
> shouldn't be affected by these patches -- I would expect it to either
> report the true value or 00s.
>
> > I will disable kptr_restrict and check or, I will enable
> > CONFIG_DEBUG_CONSOLE_UNHASHED_POINTERS and check.
>
> I would start with kptr_restrict=0 and see if that changes the contents
> of /proc/kallsyms. If it does, then it is the hashing. If it doesn't,
> well, we're back to square one. :)

Actually in that board, the kptr_restrict=0 already in both case: 4.9
and 4.14 Kernel boards.
In another board with 4.14 and kptr_restrict=2, I see that the
addresses are 00 always.

I further checked that when I enable this config:
CONFIG_DEBUG_CONSOLE_UNHASHED_POINTERS,
then the addresses are remaining the same in every boot.
But this particular config is not present in 4.9 Kernel.
So, I think it is controlled using this config.

--
Pintu