linux-kernel - Re: [PATCH v2 0/2] mm,fork,security: introduce MADV

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Message-ID: <20170809095957.kv47or2w4obaipkn@node.shutemov.name>
Date:   Wed, 9 Aug 2017 12:59:57 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Rik van Riel <riel@...hat.com>
Cc:     Michal Hocko <mhocko@...nel.org>, linux-kernel@...r.kernel.org,
        mike.kravetz@...cle.com, linux-mm@...ck.org, fweimer@...hat.com,
        colm@...costs.net, akpm@...ux-foundation.org,
        keescook@...omium.org, luto@...capital.net, wad@...omium.org,
        mingo@...nel.org, dave.hansen@...el.com, linux-api@...r.kernel.org
Subject: Re: [PATCH v2 0/2] mm,fork,security: introduce MADV_WIPEONFORK

On Mon, Aug 07, 2017 at 10:59:51AM -0400, Rik van Riel wrote:
> On Mon, 2017-08-07 at 15:46 +0200, Michal Hocko wrote:
> > On Mon 07-08-17 15:22:57, Michal Hocko wrote:
> > > This is an user visible API so make sure you CC linux-api (added)
> > > 
> > > On Sun 06-08-17 10:04:23, Rik van Riel wrote:
> > > > 
> > > > A further complication is the proliferation of clone flags,
> > > > programs bypassing glibc's functions to call clone directly,
> > > > and programs calling unshare, causing the glibc pthread_atfork
> > > > hook to not get called.
> > > > 
> > > > It would be better to have the kernel take care of this
> > > > automatically.
> > > > 
> > > > This is similar to the OpenBSD minherit syscall with
> > > > MAP_INHERIT_ZERO:
> > > > 
> > > >     https://man.openbsd.org/minherit.2
> > 
> > I would argue that a MAP_$FOO flag would be more appropriate. Or do
> > you
> > see any cases where such a special mapping would need to change the
> > semantic and inherit the content over the fork again?
> > 
> > I do not like the madvise because it is an advise and as such it can
> > be
> > ignored/not implemented and that shouldn't have any correctness
> > effects
> > on the child process.
> 
> Too late for that. VM_DONTFORK is already implemented
> through MADV_DONTFORK & MADV_DOFORK, in a way that is
> very similar to the MADV_WIPEONFORK from these patches.

It's not obvious to me what would break if kernel would ignore
MADV_DONTFORK or MADV_DONTDUMP.

-- 
 Kirill A. Shutemov