linux-hardening - Re: [PATCH] mm, hugetlb: Avoid double clearing for hugetlb pages

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Message-ID: <20201022085557.GK23790@dhcp22.suse.cz>
Date:   Thu, 22 Oct 2020 10:55:57 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     Mike Kravetz <mike.kravetz@...cle.com>,
        "Guilherme G. Piccoli" <gpiccoli@...onical.com>,
        linux-mm@...ck.org, kernel-hardening@...ts.openwall.com,
        linux-hardening@...r.kernel.org,
        linux-security-module@...r.kernel.org, kernel@...ccoli.net,
        cascardo@...onical.com, Alexander Potapenko <glider@...gle.com>,
        James Morris <jamorris@...ux.microsoft.com>,
        Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH] mm, hugetlb: Avoid double clearing for hugetlb pages

On Thu 22-10-20 10:04:50, David Hildenbrand wrote:
[...]
> > None of that would address the original point of this thread, the global
> > init_on_alloc parameter.
> 
> Yes, but I guess we're past that: whatever leaves the buddy shall be
> zeroed out. That's the whole point of that security hardening mechanism.

Hugetlb can control its zeroying behavior via mount option (for
MAP_HUGETLB controled by a command line parameter). If the page fault
handler can recognize the pre-initialized pages then both init_on* can
be implemented along with such a hugetlb specific mechanism.
-- 
Michal Hocko
SUSE Labs