Re: [PATCH v2 0/2] mm,fork,security: introduce MADV_WIPEONFORK

From: Rik van Riel <riel@redhat.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: linux-kernel@vger.kernel.org, mike.kravetz@oracle.com,
	linux-mm@kvack.org, fweimer@redhat.com, colm@allcosts.net,
	akpm@linux-foundation.org, keescook@chromium.org,
	luto@amacapital.net, wad@chromium.org, mingo@kernel.org,
	kirill@shutemov.name, dave.hansen@intel.com,
	linux-api@vger.kernel.org
Subject: Re: [PATCH v2 0/2] mm,fork,security: introduce MADV_WIPEONFORK
Date: Mon, 07 Aug 2017 10:59:51 -0400	[thread overview]
Message-ID: <1502117991.6577.13.camel@redhat.com> (raw)
In-Reply-To: <20170807134648.GI32434@dhcp22.suse.cz>

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.

I wonder if that was done because MAP_* flags are a
bitmap, with a very limited number of values as a result,
while MADV_* constants have an essentially unlimited
numerical namespace available.