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[198.145.29.99]) by mx.google.com with ESMTPS id f20si137446pgv.448.2019.07.02.15.59.16 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 02 Jul 2019 15:59:16 -0700 (PDT) Received-SPF: pass (google.com: domain of akpm@linux-foundation.org designates 198.145.29.99 as permitted sender) client-ip=198.145.29.99; Authentication-Results: mx.google.com; dkim=pass header.i=@kernel.org header.s=default header.b=uHdrGlf4; spf=pass (google.com: domain of akpm@linux-foundation.org designates 198.145.29.99 as permitted sender) smtp.mailfrom=akpm@linux-foundation.org Received: from akpm3.svl.corp.google.com (unknown [104.133.8.65]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id B896A21954; Tue, 2 Jul 2019 22:59:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1562108356; bh=iRu3VNOe2UUsUii+YtWwRL9+vOwU1d4+9aIcTU3Xflk=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=uHdrGlf41wDBUbR8nmq0GhdtDDlZO0yuNmpD6khamveWRyuhExuvwehPTjqBHRhwz hDCshEIl1r1SB5ixh6T2DjLlZDgTJZoi1YP+DJAcIwZJ/5+Z5eQBeYolBp+HAyle8g EOSCdB/5O0adv8tI4NTLTlB43TBtChALpoIMg8Ho= Date: Tue, 2 Jul 2019 15:59:15 -0700 From: Andrew Morton To: Alexander Potapenko Cc: Christoph Lameter , Kees Cook , Michal Hocko , James Morris , Masahiro Yamada , Michal Hocko , James Morris , "Serge E. Hallyn" , Nick Desaulniers , Kostya Serebryany , Dmitry Vyukov , Sandeep Patil , Laura Abbott , Randy Dunlap , Jann Horn , Mark Rutland , Marco Elver , Qian Cai , linux-mm@kvack.org, linux-security-module@vger.kernel.org, kernel-hardening@lists.openwall.com Subject: Re: [PATCH v10 1/2] mm: security: introduce init_on_alloc=1 and init_on_free=1 boot options Message-Id: <20190702155915.ab5e7053e5c0d49e84c6ed67@linux-foundation.org> In-Reply-To: <20190628093131.199499-2-glider@google.com> References: <20190628093131.199499-1-glider@google.com> <20190628093131.199499-2-glider@google.com> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.32; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit 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: On Fri, 28 Jun 2019 11:31:30 +0200 Alexander Potapenko wrote: > The new options are needed to prevent possible information leaks and > make control-flow bugs that depend on uninitialized values more > deterministic. > > This is expected to be on-by-default on Android and Chrome OS. And it > gives the opportunity for anyone else to use it under distros too via > the boot args. (The init_on_free feature is regularly requested by > folks where memory forensics is included in their threat models.) > > init_on_alloc=1 makes the kernel initialize newly allocated pages and heap > objects with zeroes. Initialization is done at allocation time at the > places where checks for __GFP_ZERO are performed. > > init_on_free=1 makes the kernel initialize freed pages and heap objects > with zeroes upon their deletion. This helps to ensure sensitive data > doesn't leak via use-after-free accesses. > > Both init_on_alloc=1 and init_on_free=1 guarantee that the allocator > returns zeroed memory. The two exceptions are slab caches with > constructors and SLAB_TYPESAFE_BY_RCU flag. Those are never > zero-initialized to preserve their semantics. > > Both init_on_alloc and init_on_free default to zero, but those defaults > can be overridden with CONFIG_INIT_ON_ALLOC_DEFAULT_ON and > CONFIG_INIT_ON_FREE_DEFAULT_ON. > > If either SLUB poisoning or page poisoning is enabled, those options > take precedence over init_on_alloc and init_on_free: initialization is > only applied to unpoisoned allocations. > > Slowdown for the new features compared to init_on_free=0, > init_on_alloc=0: > > hackbench, init_on_free=1: +7.62% sys time (st.err 0.74%) > hackbench, init_on_alloc=1: +7.75% sys time (st.err 2.14%) > > Linux build with -j12, init_on_free=1: +8.38% wall time (st.err 0.39%) > Linux build with -j12, init_on_free=1: +24.42% sys time (st.err 0.52%) > Linux build with -j12, init_on_alloc=1: -0.13% wall time (st.err 0.42%) > Linux build with -j12, init_on_alloc=1: +0.57% sys time (st.err 0.40%) > > The slowdown for init_on_free=0, init_on_alloc=0 compared to the > baseline is within the standard error. > > The new features are also going to pave the way for hardware memory > tagging (e.g. arm64's MTE), which will require both on_alloc and on_free > hooks to set the tags for heap objects. With MTE, tagging will have the > same cost as memory initialization. > > Although init_on_free is rather costly, there are paranoid use-cases where > in-memory data lifetime is desired to be minimized. There are various > arguments for/against the realism of the associated threat models, but > given that we'll need the infrastructure for MTE anyway, and there are > people who want wipe-on-free behavior no matter what the performance cost, > it seems reasonable to include it in this series. > > ... > > v10: > - added Acked-by: tags > - converted pr_warn() to pr_info() There are unchangelogged alterations between v9 and v10. The replacement of IS_ENABLED(CONFIG_PAGE_POISONING)) with page_poisoning_enabled(). --- a/mm/page_alloc.c~mm-security-introduce-init_on_alloc=1-and-init_on_free=1-boot-options-v10 +++ a/mm/page_alloc.c @@ -157,8 +157,8 @@ static int __init early_init_on_alloc(ch if (!buf) return -EINVAL; ret = kstrtobool(buf, &bool_result); - if (bool_result && IS_ENABLED(CONFIG_PAGE_POISONING)) - pr_warn("mem auto-init: CONFIG_PAGE_POISONING is on, will take precedence over init_on_alloc\n"); + if (bool_result && page_poisoning_enabled()) + pr_info("mem auto-init: CONFIG_PAGE_POISONING is on, will take precedence over init_on_alloc\n"); if (bool_result) static_branch_enable(&init_on_alloc); else @@ -175,8 +175,8 @@ static int __init early_init_on_free(cha if (!buf) return -EINVAL; ret = kstrtobool(buf, &bool_result); - if (bool_result && IS_ENABLED(CONFIG_PAGE_POISONING)) - pr_warn("mem auto-init: CONFIG_PAGE_POISONING is on, will take precedence over init_on_free\n"); + if (bool_result && page_poisoning_enabled()) + pr_info("mem auto-init: CONFIG_PAGE_POISONING is on, will take precedence over init_on_free\n"); if (bool_result) static_branch_enable(&init_on_free); else --- a/mm/slub.c~mm-security-introduce-init_on_alloc=1-and-init_on_free=1-boot-options-v10 +++ a/mm/slub.c @@ -1281,9 +1281,8 @@ check_slabs: out: if ((static_branch_unlikely(&init_on_alloc) || static_branch_unlikely(&init_on_free)) && - (slub_debug & SLAB_POISON)) { - pr_warn("mem auto-init: SLAB_POISON will take precedence over init_on_alloc/init_on_free\n"); - } + (slub_debug & SLAB_POISON)) + pr_info("mem auto-init: SLAB_POISON will take precedence over init_on_alloc/init_on_free\n"); return 1; } _