From: Ingo Molnar <mingo@kernel•org>
To: Laurent Dufour <ldufour@linux•vnet.ibm.com>
Cc: linux-arch@vger•kernel.org, linux-s390@vger•kernel.org,
x86@kernel•org, user-mode-linux-devel@lists•sourceforge.net,
Arnd Bergmann <arnd@arndb•de>, Jeff Dike <jdike@addtoit•com>,
"H. Peter Anvin" <hpa@zytor•com>,
linux-kernel@vger•kernel.org, criu@openvz•org,
linux-mm@kvack•org, Ingo Molnar <mingo@redhat•com>,
Paul Mackerras <paulus@samba•org>,
user-mode-linux-user@lists•sourceforge.net,
Richard Weinberger <richard@nod•at>,
Thomas Gleixner <tglx@linutronix•de>,
Guan Xuetao <gxt@mprc•pku.edu.cn>,
linuxppc-dev@lists•ozlabs.org, cov@codeaurora•org
Subject: Re: [PATCH v3 2/2] powerpc/mm: Tracking vDSO remap
Date: Thu, 26 Mar 2015 15:17:31 +0100 [thread overview]
Message-ID: <20150326141730.GA23060@gmail.com> (raw)
In-Reply-To: <5513E16D.1030101@linux.vnet.ibm.com>
* Laurent Dufour <ldufour@linux•vnet.ibm.com> wrote:
> > I argue we should use the right condition to clear vdso_base: if
> > the vDSO gets at least partially unmapped. Otherwise there's
> > little point in the whole patch: either correctly track whether
> > the vDSO is OK, or don't ...
>
> That's a good option, but it may be hard to achieve in the case the
> vDSO area has been splitted in multiple pieces.
>
> Not sure there is a right way to handle that, here this is a best
> effort, allowing a process to unmap its vDSO and having the
> sigreturn call done through the stack area (it has to make it
> executable).
>
> Anyway I'll dig into that, assuming that the vdso_base pointer
> should be clear if a part of the vDSO is moved or unmapped. The
> patch will be larger since I'll have to get the vDSO size which is
> private to the vdso.c file.
At least for munmap() I don't think that's a worry: once unmapped
(even if just partially), vdso_base becomes zero and won't ever be set
again.
So no need to track the zillion pieces, should there be any: Humpty
Dumpty won't be whole again, right?
> > There's also the question of mprotect(): can users mprotect() the
> > vDSO on PowerPC?
>
> Yes, mprotect() the vDSO is allowed on PowerPC, as it is on x86, and
> certainly all the other architectures. Furthermore, if it is done on
> a partial part of the vDSO it is splitting the vma...
btw., CRIU's main purpose here is to reconstruct a vDSO that was
originally randomized, but whose address must now be reproduced as-is,
right?
In that sense detecting the 'good' mremap() as your patch does should
do the trick and is certainly not objectionable IMHO - I was just
wondering whether we could make a perfect job very simply.
Thanks,
Ingo
next prev parent reply other threads:[~2015-03-26 14:17 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-03-20 15:53 [PATCH 0/2] Tracking user space vDSO remaping Laurent Dufour
2015-03-20 15:53 ` [PATCH 1/2] mm: Introducing arch_remap hook Laurent Dufour
2015-03-20 23:19 ` Richard Weinberger
2015-03-23 8:52 ` Ingo Molnar
2015-03-23 9:11 ` Laurent Dufour
2015-03-25 11:06 ` [PATCH v2 0/2] Tracking user space vDSO remaping Laurent Dufour
2015-03-25 11:06 ` [PATCH v2 1/2] mm: Introducing arch_remap hook Laurent Dufour
2015-03-25 11:06 ` [PATCH v2 2/2] powerpc/mm: Tracking vDSO remap Laurent Dufour
2015-03-25 12:11 ` Ingo Molnar
2015-03-25 13:25 ` Laurent Dufour
2015-03-25 13:53 ` [PATCH v3 0/2] Tracking user space vDSO remaping Laurent Dufour
2015-03-25 13:53 ` [PATCH v3 1/2] mm: Introducing arch_remap hook Laurent Dufour
2015-03-25 13:53 ` [PATCH v3 2/2] powerpc/mm: Tracking vDSO remap Laurent Dufour
2015-03-25 18:33 ` Ingo Molnar
2015-03-25 18:36 ` Ingo Molnar
2015-03-25 21:11 ` Benjamin Herrenschmidt
2015-03-26 9:43 ` Ingo Molnar
2015-03-26 10:37 ` Laurent Dufour
2015-03-26 14:17 ` Ingo Molnar [this message]
2015-03-26 14:32 ` Laurent Dufour
2015-03-26 17:37 ` [PATCH v4 0/2] Tracking user space vDSO remaping Laurent Dufour
2015-03-26 17:37 ` [PATCH v4 1/2] mm: Introducing arch_remap hook Laurent Dufour
2015-03-26 17:37 ` [PATCH v4 2/2] powerpc/mm: Tracking vDSO remap Laurent Dufour
2015-03-26 18:55 ` Ingo Molnar
2015-03-27 11:02 ` Laurent Dufour
2015-03-26 23:23 ` [PATCH v3 " Benjamin Herrenschmidt
2015-03-25 21:09 ` Benjamin Herrenschmidt
2015-03-26 9:48 ` Ingo Molnar
2015-03-26 10:13 ` Laurent Dufour
2015-03-20 15:53 ` [PATCH " Laurent Dufour
2016-03-02 12:13 ` [PATCH 0/2] Tracking user space vDSO remaping Christopher Covington
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