linux-kernel - Re: [PATCH V2] mm: Allow userland to request that the kernel clear memory on release

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Message-ID: <CACdnJuvU4jZJwtpcZq4_t+qujV3X_YLwo=FoDKoNmP74=z7Hng@mail.gmail.com>
Date:   Thu, 25 Apr 2019 13:45:42 -0700
From:   Matthew Garrett <mjg59@...gle.com>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Michal Hocko <mhocko@...nel.org>, Linux-MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>
Subject: Re: [PATCH V2] mm: Allow userland to request that the kernel clear
 memory on release

On Thu, Apr 25, 2019 at 5:44 AM Vlastimil Babka <vbabka@...e.cz> wrote:
>
> On 4/25/19 2:14 PM, Michal Hocko wrote:
> > Please cc linux-api for user visible API proposals (now done). Keep the
> > rest of the email intact for reference.
> >
> > On Wed 24-04-19 14:10:39, Matthew Garrett wrote:
> >> From: Matthew Garrett <mjg59@...gle.com>
> >>
> >> Applications that hold secrets and wish to avoid them leaking can use
> >> mlock() to prevent the page from being pushed out to swap and
> >> MADV_DONTDUMP to prevent it from being included in core dumps. Applications
>
> So, do we really need a new madvise() flag and VMA flag, or can we just
> infer this page clearing from mlock+MADV_DONTDUMP being both applied?

I think the combination would probably imply that this is the
behaviour you want, but I'm a little concerned about changing the
semantics given the corner cases described earlier in the thread. If
we can figure those out in a way that won't break any existing code, I
could buy this.