Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH v8 2/8] powerpc/vdso: Remove __kernel_datapage_offset and
 simplify __get_datapage()
To:     Christophe Leroy <christophe.leroy@csgroup.eu>,
        Will Deacon <will@kernel.org>,
        Michael Ellerman <mpe@ellerman.id.au>
Cc:     Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>, nathanl@linux.ibm.com,
        linux-arch <linux-arch@vger.kernel.org>,
        Arnd Bergmann <arnd@arndb.de>,
        open list <linux-kernel@vger.kernel.org>,
        Andy Lutomirski <luto@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Vincenzo Frascino <vincenzo.frascino@arm.com>,
        linuxppc-dev@lists.ozlabs.org
References: <cover.1588079622.git.christophe.leroy@c-s.fr>
 <0d2201efe3c7727f2acc718aefd7c5bb22c66c57.1588079622.git.christophe.leroy@c-s.fr>
 <87wo34tbas.fsf@mpe.ellerman.id.au>
 <2f9b7d02-9e2f-4724-2608-c5573f6507a2@csgroup.eu>
 <6862421a-5a14-2e38-b825-e39e6ad3d51d@csgroup.eu>
 <87imd5h5kb.fsf@mpe.ellerman.id.au>
 <CAJwJo6ZANqYkSHbQ+3b+Fi_VT80MtrzEV5yreQAWx-L8j8x2zA@mail.gmail.com>
 <87a6yf34aj.fsf@mpe.ellerman.id.au> <20200921112638.GC2139@willie-the-truck>
 <ad72ffd3-a552-cc98-7545-d30285fd5219@csgroup.eu>
From:   Dmitry Safonov <0x7f454c46@gmail.com>
Message-ID: <542145eb-7d90-0444-867e-c9cbb6bdd8e3@gmail.com>
Date:   Mon, 28 Sep 2020 16:08:03 +0100
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101
 Thunderbird/68.12.0
MIME-Version: 1.0
In-Reply-To: <ad72ffd3-a552-cc98-7545-d30285fd5219@csgroup.eu>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 8bit
Precedence: bulk

On 9/27/20 8:43 AM, Christophe Leroy wrote:
> 
> 
> Le 21/09/2020 à 13:26, Will Deacon a écrit :
>> On Fri, Aug 28, 2020 at 12:14:28PM +1000, Michael Ellerman wrote:
>>> Dmitry Safonov <0x7f454c46@gmail.com> writes:
[..]
>>>> I'll cook a patch for vm_special_mapping if you don't mind :-)
>>>
>>> That would be great, thanks!
>>
>> I lost track of this one. Is there a patch kicking around to resolve
>> this,
>> or is the segfault expected behaviour?
>>
> 
> IIUC dmitry said he will cook a patch. I have not seen any patch yet.

Yes, sorry about the delay - I was a bit busy with xfrm patches.

I'll send patches for .close() this week, working on them now.

> AFAIKS, among the architectures having VDSO sigreturn trampolines, only
> SH, X86 and POWERPC provide alternative trampoline on stack when VDSO is
> not there.
> 
> All other architectures just having a VDSO don't expect VDSO to not be
> mapped.
> 
> As far as nowadays stacks are mapped non-executable, getting a segfaut
> is expected behaviour. However, I think we should really make it
> cleaner. Today it segfaults because it is still pointing to the VDSO
> trampoline that has been unmapped. But should the user map some other
> code at the same address, we'll run in the weed on signal return instead
> of segfaulting.

+1.

> So VDSO unmapping should really be properly managed, the reference
> should be properly cleared in order to segfault in a controllable manner.
> 
> Only powerpc has a hook to properly clear the VDSO pointer when VDSO is
> unmapped.

Thanks,
         Dmitry