Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
From:   Pintu Agarwal <pintu.ping@gmail.com>
Date:   Fri, 25 Sep 2020 20:33:59 +0530
Message-ID: <CAOuPNLjtG_VHL1M8-=pKNNRmWQg_8oC0YG7C8H3gQcbJ+0B3=A@mail.gmail.com>
Subject: KASLR support on ARM with Kernel 4.9 and 4.14
To:     open list <linux-kernel@vger.kernel.org>,
        Kernelnewbies <kernelnewbies@kernelnewbies.org>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@lists.infradead.org>,
        Russell King - ARM Linux <linux@armlinux.org.uk>,
        ard.biesheuvel@linaro.org, arnd@arndb.de, nico@linaro.org,
        keescook@chromium.org, thgarnie@google.com, marc.zyngier@arm.com,
        Mark Rutland <mark.rutland@arm.com>, tony@atomide.com,
        matt@codeblueprint.co.uk, dave.martin@arm.com
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

Hi All,

This is regarding the KASLR feature support on ARM for the kernel
version 4.9 and 4.14.

Is KASLR supported on ARM-32 Linux 4.9 and above ?
Is it dependent on CONFIG_RANDOMIZE_BASE or
/proc/sys/kernel/randomize_va_space ?
Is there any relation between these two?
Is the changing kernel symbols (in every boot), only possible if KASLR
is enabled, or there is another way it can happen?

I have these queries because,
In one of the arm-32 devices with Kernel 4.14, I observed that
CONFIG_RANDOMIZE_BASE is not available.
But /proc/sys/kernel/randomize_va_space is set to 2.
However, I also observed that symbol addresses are changing in every boot.

1st boot cycle:
[root ~]# cat /proc/kallsyms | grep "sys_open"
a5b4de92 T sys_open
[root@sa515m ~]#

2nd boot cycle:
[root ~]# cat /proc/kallsyms | grep "sys_open"
f546ed66 T sys_open

So, I am wondering how this is possible without KASLR
(CONFIG_RANDOMIZE_BASE) support in Kernel ?

Similarly, with Kernel 4.9 and CONFIG_RANDOMIZE_BASE is not available
but /proc/sys/kernel/randomize_va_space is set to 2.
But here, the addresses are remaining same.

1st Run:
[root~]# cat /proc/kallsyms | grep "sys_open"
c01ed68c T sys_open
[root ~]#

*** reboot ***
[root ~]# cat /proc/kallsyms | grep "sys_open"
c01ed68c T sys_open


Is there any other difference between these two kernel versions with
respect to changing symbol addresses ?

Thanks,
Pintu