From: Laurent Dufour <ldufour@linux.vnet.ibm.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Michael Ellerman <mpe@ellerman.id.au>,
Dave Hansen <dave.hansen@linux.intel.com>,
LKML <linux-kernel@vger.kernel.org>,
rguenther@suse.de, mhocko@suse.com, vbabka@suse.cz,
luto@amacapital.net, x86@kernel.org,
Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org, stable@vger.kernel.org
Subject: bos
Date: Tue, 23 Apr 2019 15:36:56 +0200 [thread overview]
Message-ID: <4791a72f-901c-59cb-0553-5c32e26423f7@linux.vnet.ibm.com> (raw)
In-Reply-To: <alpine.DEB.2.21.1904231533190.9956@nanos.tec.linutronix.de>
Le 23/04/2019 à 15:34, Thomas Gleixner a écrit :
> On Tue, 23 Apr 2019, Laurent Dufour wrote:
>> Le 20/04/2019 à 12:31, Michael Ellerman a écrit :
>>> Thomas Gleixner <tglx@linutronix.de> writes:
>>>> Aside of that the powerpc variant looks suspicious:
>>>>
>>>> static inline void arch_unmap(struct mm_struct *mm,
>>>> unsigned long start, unsigned long end)
>>>> {
>>>> if (start <= mm->context.vdso_base && mm->context.vdso_base < end)
>>>> mm->context.vdso_base = 0;
>>>> }
>>>>
>>>> Shouldn't that be:
>>>>
>>>> if (start >= mm->context.vdso_base && mm->context.vdso_base < end)
>>>>
>>>> Hmm?
>>>
>>> Yeah looks pretty suspicious. I'll follow-up with Laurent who wrote it.
>>> Thanks for spotting it!
>>
>> I've to admit that I had to read that code carefully before answering.
>>
>> There are 2 assumptions here:
>> 1. 'start' and 'end' are page aligned (this is guaranteed by __do_munmap().
>> 2. the VDSO is 1 page (this is guaranteed by the union vdso_data_store on
>> powerpc).
>>
>> The idea is to handle a munmap() call surrounding the VDSO area:
>> | VDSO |
>> ^start ^end
>>
>> This is covered by this test, as the munmap() matching the exact boundaries of
>> the VDSO is handled too.
>>
>> Am I missing something ?
>
> Well if this is the intention, then you missed to add a comment explaining it :)
>
> Thanks,
>
> tglx
You're right, and I was thinking the same when I read that code this
morning ;)
I'll propose a patch to a add an explicit comment.
Thanks,
Laurent.
next prev parent reply other threads:[~2019-04-23 13:37 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-01 14:15 [PATCH] x86/mpx: fix recursive munmap() corruption Dave Hansen
2019-04-19 10:55 ` Thomas Gleixner
2019-04-20 10:31 ` Michael Ellerman
2019-04-23 11:16 ` Laurent Dufour
2019-04-23 13:34 ` Thomas Gleixner
2019-04-23 13:36 ` Laurent Dufour [this message]
2019-04-23 16:04 ` Dave Hansen
2019-04-23 17:07 ` Laurent Dufour
2019-05-01 10:32 ` Michael Ellerman
2019-05-07 16:35 ` Laurent Dufour
2020-10-23 12:28 ` Christophe Leroy
2020-11-03 17:11 ` Laurent Dufour
2020-11-03 21:08 ` Dmitry Safonov
2020-11-04 9:41 ` Laurent Dufour
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