linux-kernel - Re: [PATCH 0/2] mm,fork,security: introduce MADV

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Date:   Sat, 05 Aug 2017 11:21:44 -0400
From:   Rik van Riel <riel@...hat.com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        fweimer@...hat.com, colm@...costs.net, akpm@...ux-foundation.org,
        rppt@...ux.vnet.ibm.com, keescook@...omium.org,
        luto@...capital.net, wad@...omium.org, mingo@...nel.org
Subject: Re: [PATCH 0/2] mm,fork,security: introduce MADV_WIPEONFORK

On Sat, 2017-08-05 at 02:44 +0300, Kirill A. Shutemov wrote:
> On Fri, Aug 04, 2017 at 03:07:28PM -0400, riel@...hat.com wrote:
> > [resend because half the recipients got dropped due to IPv6
> > firewall issues]
> > 
> > Introduce MADV_WIPEONFORK semantics, which result in a VMA being
> > empty in the child process after fork. This differs from
> > MADV_DONTFORK
> > in one important way.
> > 
> > If a child process accesses memory that was MADV_WIPEONFORK, it
> > will get zeroes. The address ranges are still valid, they are just
> > empty.
> 
> I feel like we are repeating mistake we made with MADV_DONTNEED.
> 
> MADV_WIPEONFORK would require a specific action from kernel, ignoring
> the /advise/ would likely lead to application misbehaviour.
> 
> Is it something we really want to see from madvise()?

We already have various mandatory madvise behaviors in Linux,
including MADV_REMOVE, MADV_DONTFORK, and MADV_DONTDUMP.