From: Laurent Dufour <ldufour@linux•vnet.ibm.com>
To: Ingo Molnar <mingo@kernel•org>,
Benjamin Herrenschmidt <benh@kernel•crashing.org>
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>,
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 11:13:53 +0100 [thread overview]
Message-ID: <5513DBE1.4070404@linux.vnet.ibm.com> (raw)
In-Reply-To: <20150326094844.GB15407@gmail.com>
On 26/03/2015 10:48, Ingo Molnar wrote:
>
> * Benjamin Herrenschmidt <benh@kernel•crashing.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.
>>>
>>> In particular, what happens if an mremap() is done with
>>> old_start == vdso_base, but a shorter end than the end of the vDSO?
>>> (i.e. a partial mremap() with fewer pages than the vDSO size)
>>
>> Is there a way to forbid splitting ? Does x86 deal with that case at
>> all or it doesn't have to for some other reason ?
>
> So we use _install_special_mapping() - maybe PowerPC does that too?
> That adds VM_DONTEXPAND which ought to prevent some - but not all - of
> the VM API weirdnesses.
The same is done on PowerPC. So calling mremap() to extend the vDSO is
failing but splitting it or unmapping a part of it is allowed but lead
to an unusable vDSO.
> On x86 we'll just dump core if someone unmaps the vdso.
On PowerPC, you'll get the same result.
Should we prevent the user to break its vDSO ?
Thanks,
Laurent.
next prev parent reply other threads:[~2015-03-26 10:14 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
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 [this message]
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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