[Query] ARM64 kaslr support - randomness, seeding and kdump

From: bhsharma@redhat.com (Bhupesh Sharma)
To: linux-arm-kernel@lists.infradead.org
Subject: [Query] ARM64 kaslr support - randomness, seeding and kdump
Date: Fri, 16 Mar 2018 15:05:10 +0530	[thread overview]
Message-ID: <CACi5LpNyx5VKO6mYB1yXNPENPKhAfAJ7cUSBeVzVtXfF6+EPwg@mail.gmail.com> (raw)
In-Reply-To: <20180314182448.bnvjtgyzipsuxcbe@lakrids.cambridge.arm.com>

On Wed, Mar 14, 2018 at 11:54 PM, Mark Rutland <mark.rutland@arm.com> wrote:
> On Wed, Mar 14, 2018 at 11:10:53AM +0900, AKASHI Takahiro wrote:
>> If kaslr-seed has a critical value in terms of security, is kexec-tools
>> a right place? It is exposed to user space albeit for a short time of period.
>
> The kernel zeroes the seed in the DT at boot time, so the current seed
> isn't visible to userspace.
>
> If kexec-tools generates a seed, and inserts it into the DTB that it
> loads, this is only visible to kexec tools or other applications which
> can inspect its memory, so I don't think this is much of a concern.
> Anything with such privilege can presumably kexec() to arbitrary code
> anyhow.
>
> The next kernel will then zero its seed in the DT at boot time, so
> similarly this won't be visible to userspace on the new kernel.
>
> FWIW, having kexec tools generate a seed for the kexec_load() case makes
> sense to me.

Fair enough. I will try to take a stab at the same and come back with
my findings on this thread.

Thanks,
Bhupesh