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[192.55.52.151]) by mx.google.com with ESMTPS id h17si2741163pfj.38.2019.04.18.09.52.21 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 18 Apr 2019 09:52:22 -0700 (PDT) Received-SPF: pass (google.com: domain of dave.hansen@intel.com designates 192.55.52.151 as permitted sender) client-ip=192.55.52.151; Authentication-Results: mx.google.com; spf=pass (google.com: domain of dave.hansen@intel.com designates 192.55.52.151 as permitted sender) smtp.mailfrom=dave.hansen@intel.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=intel.com X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga004.jf.intel.com ([10.7.209.38]) by fmsmga107.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 18 Apr 2019 09:52:21 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.60,366,1549958400"; d="scan'208";a="292660378" Received: from ray.jf.intel.com (HELO [10.7.201.126]) ([10.7.201.126]) by orsmga004.jf.intel.com with ESMTP; 18 Apr 2019 09:52:21 -0700 Subject: Re: [PATCH 2/3] gfp: mm: introduce __GFP_NOINIT To: Alexander Potapenko , akpm@linux-foundation.org, cl@linux.com, dvyukov@google.com, keescook@chromium.org, labbott@redhat.com Cc: linux-mm@kvack.org, linux-security-module@vger.kernel.org, kernel-hardening@lists.openwall.com References: <20190418154208.131118-1-glider@google.com> <20190418154208.131118-3-glider@google.com> From: Dave Hansen Openpgp: preference=signencrypt Autocrypt: addr=dave.hansen@intel.com; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <20190418154208.131118-3-glider@google.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit 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 4/18/19 8:42 AM, Alexander Potapenko wrote: > __GFP_NOINIT basically defeats the hardening against information leaks > provided by the init_allocations feature, so one should use it with > caution. Even more than that, shouldn't we try to use it only in places where there is a demonstrated benefit, like performance data? > diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c > index be84f5f95c97..f9d1f1236cd0 100644 > --- a/kernel/kexec_core.c > +++ b/kernel/kexec_core.c > @@ -302,7 +302,7 @@ static struct page *kimage_alloc_pages(gfp_t gfp_mask, unsigned int order) > { > struct page *pages; > > - pages = alloc_pages(gfp_mask & ~__GFP_ZERO, order); > + pages = alloc_pages((gfp_mask & ~__GFP_ZERO) | __GFP_NOINIT, order); > if (pages) { > unsigned int count, i; While this is probably not super security-sensitive, it's also not performance sensitive. > diff --git a/mm/slab.c b/mm/slab.c > index dcc5b73cf767..762cb0e7bcc1 100644 > --- a/mm/slab.c > +++ b/mm/slab.c > @@ -1393,7 +1393,7 @@ static struct page *kmem_getpages(struct kmem_cache *cachep, gfp_t flags, > struct page *page; > int nr_pages; > > - flags |= cachep->allocflags; > + flags |= (cachep->allocflags | __GFP_NOINIT); > > page = __alloc_pages_node(nodeid, flags, cachep->gfporder); > if (!page) { > diff --git a/mm/slob.c b/mm/slob.c > index 18981a71e962..867d2d68a693 100644 > --- a/mm/slob.c > +++ b/mm/slob.c > @@ -192,6 +192,7 @@ static void *slob_new_pages(gfp_t gfp, int order, int node) > { > void *page; > > + gfp |= __GFP_NOINIT; > #ifdef CONFIG_NUMA > if (node != NUMA_NO_NODE) > page = __alloc_pages_node(node, gfp, order > diff --git a/mm/slub.c b/mm/slub.c > index e4efb6575510..a79b4cb768a2 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -1493,6 +1493,7 @@ static inline struct page *alloc_slab_page(struct kmem_cache *s, > struct page *page; > unsigned int order = oo_order(oo); > > + flags |= __GFP_NOINIT; > if (node == NUMA_NO_NODE) > page = alloc_pages(flags, order); > else > These sl*b ones seem like a bad idea. We already have rules that sl*b allocations must be initialized by callers, and we have reasonably frequent bugs where the rules are broken. Setting __GFP_NOINIT might be reasonable to do, though, for slabs that have a constructor. We have much higher confidence that *those* are going to get initialized properly.