From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753137AbcEWWKi (ORCPT ); Mon, 23 May 2016 18:10:38 -0400 Received: from mail-wm0-f68.google.com ([74.125.82.68]:33540 "EHLO mail-wm0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753046AbcEWWKg (ORCPT ); Mon, 23 May 2016 18:10:36 -0400 Date: Tue, 24 May 2016 00:17:36 +0200 From: Emese Revfy To: kernel-hardening@lists.openwall.com Cc: pageexec@freemail.hu, spender@grsecurity.net, mmarek@suse.com, keescook@chromium.org, linux-kernel@vger.kernel.org, yamada.masahiro@socionext.com, linux-kbuild@vger.kernel.org, tytso@mit.edu, akpm@linux-foundation.org, linux-mm@kvack.org, axboe@kernel.dk, viro@zeniv.linux.org.uk, paulmck@linux.vnet.ibm.com, mingo@redhat.com, tglx@linutronix.de, bart.vanassche@sandisk.com, davem@davemloft.net Subject: [PATCH v1 3/3] Add the extra_latent_entropy kernel parameter Message-Id: <20160524001736.135ae3cdc101ecec3232a493@gmail.com> In-Reply-To: <20160524001405.3e6abd1d5a63a871cc366cff@gmail.com> References: <20160524001405.3e6abd1d5a63a871cc366cff@gmail.com> X-Mailer: Sylpheed 3.5.0 (GTK+ 2.24.30; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org When extra_latent_entropy is passed on the kernel command line, entropy will be extracted from up to the first 4GB of RAM while the runtime memory allocator is being initialized. Based on work created by the PaX Team. Signed-off-by: Emese Revfy --- Documentation/kernel-parameters.txt | 5 +++++ arch/Kconfig | 5 +++++ mm/page_alloc.c | 23 +++++++++++++++++++++++ 3 files changed, 33 insertions(+) diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index 5349363..6c2496e 100644 --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -2862,6 +2862,11 @@ bytes respectively. Such letter suffixes can also be entirely omitted. the specified number of seconds. This is to be used if your oopses keep scrolling off the screen. + extra_latent_entropy + Enable a very simple form of latent entropy extraction + from the first 4GB of memory as the bootmem allocator + passes the memory pages to the buddy allocator. + pcbit= [HW,ISDN] pcd. [PARIDE] diff --git a/arch/Kconfig b/arch/Kconfig index 74489df..327d1e4 100644 --- a/arch/Kconfig +++ b/arch/Kconfig @@ -403,6 +403,11 @@ config GCC_PLUGIN_LATENT_ENTROPY there is little 'natural' source of entropy normally. The cost is some slowdown of the boot process and fork and irq processing. + When extra_latent_entropy is passed on the kernel command line, + entropy will be extracted from up to the first 4GB of RAM while the + runtime memory allocator is being initialized. This costs even more + slowdown of the boot process. + Note that entropy extracted this way is not known to be cryptographically secure! diff --git a/mm/page_alloc.c b/mm/page_alloc.c index ffc4f4a..c79407b 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -63,6 +63,7 @@ #include #include #include +#include #include #include @@ -1235,6 +1236,15 @@ static void __free_pages_ok(struct page *page, unsigned int order) } #ifdef CONFIG_GCC_PLUGIN_LATENT_ENTROPY +bool __meminitdata extra_latent_entropy; + +static int __init setup_extra_latent_entropy(char *str) +{ + extra_latent_entropy = true; + return 0; +} +early_param("extra_latent_entropy", setup_extra_latent_entropy); + volatile u64 latent_entropy __latent_entropy; EXPORT_SYMBOL(latent_entropy); #endif @@ -1254,6 +1264,19 @@ static void __init __free_pages_boot_core(struct page *page, unsigned int order) __ClearPageReserved(p); set_page_count(p, 0); +#ifdef CONFIG_GCC_PLUGIN_LATENT_ENTROPY + if (extra_latent_entropy && !PageHighMem(page) && page_to_pfn(page) < 0x100000) { + u64 hash = 0; + size_t index, end = PAGE_SIZE * nr_pages / sizeof hash; + const u64 *data = lowmem_page_address(page); + + for (index = 0; index < end; index++) + hash ^= hash + data[index]; + latent_entropy ^= hash; + add_device_randomness((const void *)&latent_entropy, sizeof(latent_entropy)); + } +#endif + page_zone(page)->managed_pages += nr_pages; set_page_refcounted(page); __free_pages(page, order); -- 2.8.1