From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f200.google.com (mail-pf0-f200.google.com [209.85.192.200]) by kanga.kvack.org (Postfix) with ESMTP id C094D6B0005 for ; Wed, 10 Aug 2016 18:28:08 -0400 (EDT) Received: by mail-pf0-f200.google.com with SMTP id 63so104161448pfx.0 for ; Wed, 10 Aug 2016 15:28:08 -0700 (PDT) Received: from mail-pf0-x22f.google.com (mail-pf0-x22f.google.com. [2607:f8b0:400e:c00::22f]) by mx.google.com with ESMTPS id k7si50564937pag.88.2016.08.10.15.28.07 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 10 Aug 2016 15:28:07 -0700 (PDT) Received: by mail-pf0-x22f.google.com with SMTP id y134so19983633pfg.0 for ; Wed, 10 Aug 2016 15:28:07 -0700 (PDT) Date: Wed, 10 Aug 2016 15:28:05 -0700 From: Kees Cook Subject: [PATCH] mm: Add the ram_latent_entropy kernel parameter Message-ID: <20160810222805.GA13733@www.outflux.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Sender: owner-linux-mm@kvack.org List-ID: To: linux-kernel@vger.kernel.org Cc: Linus Torvalds , Emese Revfy , Andrew Morton , Jonathan Corbet , Vlastimil Babka , Mel Gorman , Michal Hocko , Johannes Weiner , Joonsoo Kim , "Kirill A. Shutemov" , Taku Izumi , linux-doc@vger.kernel.org, linux-mm@kvack.org, kernel-hardening@lists.openwall.com From: Emese Revfy When "ram_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 entropy isn't cryptographically secure, but does help provide additional unpredictability on otherwise low-entropy systems. Based on work created by the PaX Team. Signed-off-by: Emese Revfy [kees: renamed parameter, dropped relationship with plugin, updated log] Signed-off-by: Kees Cook --- This patch has been extracted from the latent_entropy gcc plugin, as suggested by Linus: https://lkml.org/lkml/2016/8/8/840 --- Documentation/kernel-parameters.txt | 5 +++++ mm/page_alloc.c | 21 +++++++++++++++++++++ 2 files changed, 26 insertions(+) diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index 46c030a49186..9d054984370f 100644 --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -3245,6 +3245,11 @@ bytes respectively. Such letter suffixes can also be entirely omitted. raid= [HW,RAID] See Documentation/md.txt. + ram_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. + ramdisk_size= [RAM] Sizes of RAM disks in kilobytes See Documentation/blockdev/ramdisk.txt. diff --git a/mm/page_alloc.c b/mm/page_alloc.c index fb975cec3518..1de94f0ff29d 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -64,6 +64,7 @@ #include #include #include +#include #include #include @@ -1236,6 +1237,15 @@ static void __free_pages_ok(struct page *page, unsigned int order) local_irq_restore(flags); } +bool __meminitdata ram_latent_entropy; + +static int __init setup_ram_latent_entropy(char *str) +{ + ram_latent_entropy = true; + return 0; +} +early_param("ram_latent_entropy", setup_ram_latent_entropy); + static void __init __free_pages_boot_core(struct page *page, unsigned int order) { unsigned int nr_pages = 1 << order; @@ -1251,6 +1261,17 @@ static void __init __free_pages_boot_core(struct page *page, unsigned int order) __ClearPageReserved(p); set_page_count(p, 0); + if (ram_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]; + add_device_randomness((const void *)&hash, sizeof(hash)); + } + page_zone(page)->managed_pages += nr_pages; set_page_refcounted(page); __free_pages(page, order); -- 2.7.4 -- Kees Cook Nexus Security -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org