From: Ingo Molnar <mingo@kernel•org>
To: Benjamin Herrenschmidt <benh@kernel•crashing.org>
Cc: linux-arch@vger•kernel.org, linux-s390@vger•kernel.org,
Laurent Dufour <ldufour@linux•vnet.ibm.com>,
user-mode-linux-devel@lists•sourceforge.net,
Arnd Bergmann <arnd@arndb•de>, Jeff Dike <jdike@addtoit•com>,
"H. Peter Anvin" <hpa@zytor•com>,
x86@kernel•org, linux-kernel@vger•kernel.org, criu@openvz•org,
linux-mm@kvack•org, Ingo Molnar <mingo@redhat•com>,
Paul Mackerras <paulus@samba•org>,
cov@codeaurora•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
Subject: Re: [PATCH v3 2/2] powerpc/mm: Tracking vDSO remap
Date: Thu, 26 Mar 2015 10:43:30 +0100 [thread overview]
Message-ID: <20150326094330.GA15407@gmail.com> (raw)
In-Reply-To: <1427317867.6468.87.camel@kernel.crashing.org>
* Benjamin Herrenschmidt <benh@kernel•crashing.org> wrote:
> On Wed, 2015-03-25 at 19:36 +0100, Ingo Molnar wrote:
> > * Ingo Molnar <mingo@kernel•org> wrote:
> >
> > > > +#define __HAVE_ARCH_REMAP
> > > > +static inline void arch_remap(struct mm_struct *mm,
> > > > + unsigned long old_start, unsigned long old_end,
> > > > + unsigned long new_start, unsigned long new_end)
> > > > +{
> > > > + /*
> > > > + * mremap() doesn't allow moving multiple vmas so we can limit the
> > > > + * check to old_start == vdso_base.
> > > > + */
> > > > + if (old_start == mm->context.vdso_base)
> > > > + mm->context.vdso_base = new_start;
> > > > +}
> > >
> > > mremap() doesn't allow moving multiple vmas, but it allows the
> > > movement of multi-page vmas and it also allows partial mremap()s,
> > > where it will split up a vma.
> >
> > I.e. mremap() supports the shrinking (and growing) of vmas. In that
> > case mremap() will unmap the end of the vma and will shrink the
> > remaining vDSO vma.
> >
> > Doesn't that result in a non-working vDSO that should zero out
> > vdso_base?
>
> Right. Now we can't completely prevent the user from shooting itself
> in the foot I suppose, though there is a legit usage scenario which
> is to move the vDSO around which it would be nice to support. I
> think it's reasonable to put the onus on the user here to do the
> right thing.
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 ...
There's also the question of mprotect(): can users mprotect() the vDSO
on PowerPC?
Thanks,
Ingo
next prev parent reply other threads:[~2015-03-26 9:43 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 [this message]
2015-03-26 10:37 ` Laurent Dufour
2015-03-26 14:17 ` Ingo Molnar
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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