From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lf0-f72.google.com (mail-lf0-f72.google.com [209.85.215.72]) by kanga.kvack.org (Postfix) with ESMTP id 2E12C6B0261 for ; Tue, 24 May 2016 13:09:19 -0400 (EDT) Received: by mail-lf0-f72.google.com with SMTP id s130so12359232lfs.2 for ; Tue, 24 May 2016 10:09:19 -0700 (PDT) Received: from mail-wm0-x22b.google.com (mail-wm0-x22b.google.com. [2a00:1450:400c:c09::22b]) by mx.google.com with ESMTPS id m10si24753790wmg.50.2016.05.24.10.09.17 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 24 May 2016 10:09:17 -0700 (PDT) Received: by mail-wm0-x22b.google.com with SMTP id z87so32287814wmh.0 for ; Tue, 24 May 2016 10:09:17 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <20160524001736.135ae3cdc101ecec3232a493@gmail.com> References: <20160524001405.3e6abd1d5a63a871cc366cff@gmail.com> <20160524001736.135ae3cdc101ecec3232a493@gmail.com> From: Kees Cook Date: Tue, 24 May 2016 10:09:16 -0700 Message-ID: Subject: Re: [PATCH v1 3/3] Add the extra_latent_entropy kernel parameter Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: Emese Revfy Cc: "kernel-hardening@lists.openwall.com" , PaX Team , Brad Spengler , Michal Marek , LKML , Masahiro Yamada , linux-kbuild , Theodore Ts'o , Andrew Morton , Linux-MM , Jens Axboe , Al Viro , Paul McKenney , Ingo Molnar , Thomas Gleixner , bart.vanassche@sandisk.com, "David S. Miller" On Mon, May 23, 2016 at 3:17 PM, Emese Revfy wrote: > 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 > + We try to minimize #ifdefs in the .c code, so in this case, I think I would define "extra_latent_entropy" during an #else above so this "if" can be culled by the compiler automatically: #else # define extra_latent_entropy false #endif Others may have better suggestions to avoid the second #ifdef, but this seems the cleanest way to me to tie this to the earlier #ifdef. -Kees > page_zone(page)->managed_pages += nr_pages; > set_page_refcounted(page); > __free_pages(page, order); > -- > 2.8.1 > -- Kees Cook Chrome OS & Brillo Security -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. 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