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[195.135.220.15]) by mx.google.com with ESMTPS id ka15si5588408ejb.266.2019.05.17.05.59.18 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 17 May 2019 05:59:19 -0700 (PDT) Received-SPF: softfail (google.com: domain of transitioning mhocko@kernel.org does not designate 195.135.220.15 as permitted sender) client-ip=195.135.220.15; Authentication-Results: mx.google.com; spf=softfail (google.com: domain of transitioning mhocko@kernel.org does not designate 195.135.220.15 as permitted sender) smtp.mailfrom=mhocko@kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=kernel.org X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 5168EAB92; Fri, 17 May 2019 12:59:18 +0000 (UTC) Date: Fri, 17 May 2019 14:59:16 +0200 From: Michal Hocko To: Alexander Potapenko Cc: akpm@linux-foundation.org, cl@linux.com, keescook@chromium.org, kernel-hardening@lists.openwall.com, Masahiro Yamada , James Morris , "Serge E. Hallyn" , Nick Desaulniers , Kostya Serebryany , Dmitry Vyukov , Sandeep Patil , Laura Abbott , Randy Dunlap , Jann Horn , Mark Rutland , Souptick Joarder , Matthew Wilcox , linux-mm@kvack.org, linux-security-module@vger.kernel.org Subject: Re: [PATCH v2 3/4] gfp: mm: introduce __GFP_NO_AUTOINIT Message-ID: <20190517125916.GF1825@dhcp22.suse.cz> References: <20190514143537.10435-1-glider@google.com> <20190514143537.10435-4-glider@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190514143537.10435-4-glider@google.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: [It would be great to keep people involved in the previous version in the CC list] On Tue 14-05-19 16:35:36, Alexander Potapenko wrote: > When passed to an allocator (either pagealloc or SL[AOU]B), > __GFP_NO_AUTOINIT tells it to not initialize the requested memory if the > init_on_alloc boot option is enabled. This can be useful in the cases > newly allocated memory is going to be initialized by the caller right > away. > > __GFP_NO_AUTOINIT doesn't affect init_on_free behavior, except for SLOB, > where init_on_free implies init_on_alloc. > > __GFP_NO_AUTOINIT basically defeats the hardening against information > leaks provided by init_on_alloc, so one should use it with caution. > > This patch also adds __GFP_NO_AUTOINIT to alloc_pages() calls in SL[AOU]B. > Doing so is safe, because the heap allocators initialize the pages they > receive before passing memory to the callers. I still do not like the idea of a new gfp flag as explained in the previous email. People will simply use it incorectly or arbitrarily. We have that juicy experience from the past. Freeing a memory is an opt-in feature and the slab allocator can already tell many (with constructor or GFP_ZERO) do not need it. So can we go without this gfp thing and see whether somebody actually finds a performance problem with the feature enabled and think about what can we do about it rather than add this maint. nightmare from the very beginning? -- Michal Hocko SUSE Labs