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Subject: Re: SLAB_TYPESAFE_BY_RCU without constructors (was Re: [PATCH v4
 13/17] khwasan: add hooks implementation)
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From: Eric Dumazet <eric.dumazet@gmail.com>
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Date: Wed, 1 Aug 2018 04:28:47 -0700
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To: Dmitry Vyukov <dvyukov@google.com>, Eric Dumazet <eric.dumazet@gmail.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>, Linus Torvalds <torvalds@linux-foundation.org>, Christoph Lameter <cl@linux.com>, Theodore Ts'o <tytso@mit.edu>, Jan Kara <jack@suse.com>, linux-ext4@vger.kernel.org, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Pablo Neira Ayuso <pablo@netfilter.org>, Jozsef Kadlecsik <kadlec@blackhole.kfki.hu>, Florian Westphal <fw@strlen.de>, David Miller <davem@davemloft.net>, NetFilter <netfilter-devel@vger.kernel.org>, coreteam@netfilter.org, Network Development <netdev@vger.kernel.org>, Gerrit Renker <gerrit@erg.abdn.ac.uk>, dccp@vger.kernel.org, Jani Nikula <jani.nikula@linux.intel.com>, Joonas Lahtinen <joonas.lahtinen@linux.intel.com>, Rodrigo Vivi <rodrigo.vivi@intel.com>, Dave Airlie <airlied@linux.ie>, intel-gfx <intel-gfx@lists.freedesktop.org>, DRI <dri-devel@lists.freedesktop.org>, Eric Dumazet <edumazet@google.com>, Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>, Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>, Ursula Braun <ubraun@linux.ibm.com>, linux-s390 <linux-s390@vger.kernel.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Andrew Morton <akpm@linux-foundation.org>, linux-mm <linux-mm@kvack.org>, Andrey Konovalov <andreyknvl@google.com>



On 08/01/2018 03:34 AM, Dmitry Vyukov wrote:
> On Wed, Aug 1, 2018 at 12:23 PM, Eric Dumazet <eric.dumazet@gmail.com> wrote:
>> On 08/01/2018 02:03 AM, Andrey Ryabinin wrote:
>>
>>> I can't think of any advantage in not having the constructor.
>>
>> I can't see any advantage adding another indirect call,
>> in RETPOLINE world.
> 
> Can you please elaborate what's the problem here?
> If slab ctor call have RETPOLINE, then using ctors more does not
> introduce any security problems and they are not _that_ slow.

They _are_ slow, when we have dozens of them in a code path.

I object "having to add" yet another indirect call, if this can be avoided [*]

If some people want to use ctor, fine, but do not request this.

[*] This can be tricky, but worth the pain.