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

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Message-ID: <634a44b5-5947-df02-be63-a68f7b317949@redhat.com>
Date:   Fri, 23 Oct 2020 10:23:07 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Michal Hocko <mhocko@...e.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 22.10.20 10:55, Michal Hocko wrote:
> 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

Right, looking at init_on_alloc tells you if you have to zero after
alloc or if it's already been done even though you didn't pass GFP_ZERO.

-- 
Thanks,

David / dhildenb