linux-kernel - Re: [patch] mremap.2: Add description of old

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Mon, 25 Sep 2017 14:35:08 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Florian Weimer <fweimer@...hat.com>
Cc:     Mike Kravetz <mike.kravetz@...cle.com>, mtk.manpages@...il.com,
        linux-man@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-api@...r.kernel.org, Andrea Arcangeli <aarcange@...hat.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Anshuman Khandual <khandual@...ux.vnet.ibm.com>,
        linux-mm@...ck.org
Subject: Re: [patch] mremap.2: Add description of old_size == 0 functionality

On Tue 19-09-17 14:11:19, Florian Weimer wrote:
> On 09/18/2017 07:11 PM, Mike Kravetz wrote:
[...]
> > I can drop this wording, but would still like to suggest memfd_create as
> > the preferred method of creating duplicate mappings.  It would be good if
> > others on Cc: could comment as well.
> 
> mremap seems to work with non-anonymous mappings, too:

only for shared mappings in fact. Because once we have CoW then mremap
will not provide you with the same content as the original mapping.

[...]

> > Just curious, does glibc make use of this today?  Or, is this just something
> > that you think may be useful.
> 
> To my knowledge, we do not use this today.  But it certainly looks very
> useful.

What would be the usecase. I mean why don't you simply create a new
mapping by a plain mmap when you have no guarantee about the same
content?
-- 
Michal Hocko
SUSE Labs