linux-kernel - Re: [PATCH] sysctl: add config to make randomize_va

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Date:   Fri, 5 May 2023 11:23:24 -0400
From:   Paul Moore <paul@...l-moore.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     Sam James <sam@...too.org>,
        Michael McCracken <michael.mccracken@...il.com>,
        linux-kernel@...r.kernel.org, serge@...lyn.com, tycho@...ho.pizza,
        Luis Chamberlain <mcgrof@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Iurii Zaikin <yzaikin@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH] sysctl: add config to make randomize_va_space RO

On Fri, May 5, 2023 at 11:15 AM David Hildenbrand <david@...hat.com> wrote:
> On 05.05.23 09:46, Sam James wrote:
> > David Hildenbrand <david@...hat.com> writes:
> >> On 04.05.23 23:30, Michael McCracken wrote:
> >>> Add config RO_RANDMAP_SYSCTL to set the mode of the randomize_va_space
> >>> sysctl to 0444 to disallow all runtime changes. This will prevent
> >>> accidental changing of this value by a root service.
> >>> The config is disabled by default to avoid surprises.

...

> If we really care, not sure what's better: maybe we want to disallow
> disabling it only in a security lockdown kernel?

If we're bringing up the idea of Lockdown, controlling access to
randomize_va_space is possible with the use of LSMs.  One could easily
remove write access to randomize_va_space, even for tasks running as
root.

(On my Rawhide system with SELinux enabled)
% ls -Z /proc/sys/kernel/randomize_va_space
system_u:object_r:proc_security_t:s0 /proc/sys/kernel/randomize_va_space

-- 
paul-moore.com