linux-kernel - Re: SLAB_TYPESAFE_BY_RCU without constructors (was Re: [PATCH v4 13/17] khwasan: add hooks implementation)

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Message-ID: <cf751136-c459-853a-0210-abf16f54ad17@gmail.com>
Date:   Wed, 1 Aug 2018 04:28:47 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Dmitry Vyukov <dvyukov@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>
Cc:     Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Christoph Lameter <cl@...ux.com>,
        Theodore Ts'o <tytso@....edu>, Jan Kara <jack@...e.com>,
        linux-ext4@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Jozsef Kadlecsik <kadlec@...ckhole.kfki.hu>,
        Florian Westphal <fw@...len.de>,
        David Miller <davem@...emloft.net>,
        NetFilter <netfilter-devel@...r.kernel.org>,
        coreteam@...filter.org,
        Network Development <netdev@...r.kernel.org>,
        Gerrit Renker <gerrit@....abdn.ac.uk>, dccp@...r.kernel.org,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Dave Airlie <airlied@...ux.ie>,
        intel-gfx <intel-gfx@...ts.freedesktop.org>,
        DRI <dri-devel@...ts.freedesktop.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Ursula Braun <ubraun@...ux.ibm.com>,
        linux-s390 <linux-s390@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-mm <linux-mm@...ck.org>,
        Andrey Konovalov <andreyknvl@...gle.com>
Subject: Re: SLAB_TYPESAFE_BY_RCU without constructors (was Re: [PATCH v4
 13/17] khwasan: add hooks implementation)



On 08/01/2018 03:34 AM, Dmitry Vyukov wrote:
> On Wed, Aug 1, 2018 at 12:23 PM, Eric Dumazet <eric.dumazet@...il.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.