From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ig0-f197.google.com (mail-ig0-f197.google.com [209.85.213.197]) by kanga.kvack.org (Postfix) with ESMTP id E6D816B0253 for ; Mon, 18 Apr 2016 15:52:31 -0400 (EDT) Received: by mail-ig0-f197.google.com with SMTP id fn8so179795801igb.1 for ; Mon, 18 Apr 2016 12:52:31 -0700 (PDT) Received: from mail-ob0-x233.google.com (mail-ob0-x233.google.com. [2607:f8b0:4003:c01::233]) by mx.google.com with ESMTPS id l136si2670026oig.36.2016.04.18.12.52.30 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 18 Apr 2016 12:52:30 -0700 (PDT) Received: by mail-ob0-x233.google.com with SMTP id tz8so102657305obc.0 for ; Mon, 18 Apr 2016 12:52:30 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <57153751.7080800@redhat.com> References: <1460741159-51752-1-git-send-email-thgarnie@google.com> <20160415150026.65abbdd5b2ef741cd070c769@linux-foundation.org> <1460759160.19090.50.camel@perches.com> <57153751.7080800@redhat.com> Date: Mon, 18 Apr 2016 12:52:30 -0700 Message-ID: Subject: Re: [PATCH] mm: SLAB freelist randomization From: Thomas Garnier Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: Laura Abbott Cc: Joe Perches , Andrew Morton , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Kees Cook , Greg Thelen , Laura Abbott , kernel-hardening@lists.openwall.com, LKML , Linux-MM I agree, if we had a generic way to pass entropy across boots on all architecture that would be amazing. I will let the SLAB maintainers to decide on requiring CONFIG_ARCH_RANDOM or documenting it. On Mon, Apr 18, 2016 at 12:36 PM, Laura Abbott wrote: > On 04/18/2016 08:59 AM, Thomas Garnier wrote: >> >> I will send the next version today. Note that I get_random_bytes_arch >> is used because at that stage we have 0 bits of entropy. It seemed >> like a better idea to use the arch version that will fallback on >> get_random_bytes sub API in the worse case. >> > > This is unfortunate for ARM/ARM64. Those platforms don't have a standard > method for getting random numbers so until additional entropy is added > get_random_bytes will always return the same seed and indeed I always > see the same shuffle on a quick test of arm64. For KASLR, the workaround > was to require the bootloader to pass in entropy. It might be good to > either document this or require this only be used with CONFIG_ARCH_RANDOM. > > > >> On Fri, Apr 15, 2016 at 3:47 PM, Thomas Garnier >> wrote: >>> >>> Thanks for the comments. I will address them in a v2 early next week. >>> >>> If anyone has other comments, please let me know. >>> >>> Thomas >>> >>> On Fri, Apr 15, 2016 at 3:26 PM, Joe Perches wrote: >>>> >>>> On Fri, 2016-04-15 at 15:00 -0700, Andrew Morton wrote: >>>>> >>>>> On Fri, 15 Apr 2016 10:25:59 -0700 Thomas Garnier >>>>> wrote: >>>>>> >>>>>> Provide an optional config (CONFIG_FREELIST_RANDOM) to randomize the >>>>>> SLAB freelist. The list is randomized during initialization of a new >>>>>> set >>>>>> of pages. The order on different freelist sizes is pre-computed at >>>>>> boot >>>>>> for performance. This security feature reduces the predictability of >>>>>> the >>>>>> kernel SLAB allocator against heap overflows rendering attacks much >>>>>> less >>>>>> stable. >>>> >>>> >>>> trivia: >>>> >>>>>> @@ -1229,6 +1229,61 @@ static void __init set_up_node(struct >>>>>> kmem_cache *cachep, int index) >>>> >>>> [] >>>>>> >>>>>> + */ >>>>>> +static freelist_idx_t master_list_2[2]; >>>>>> +static freelist_idx_t master_list_4[4]; >>>>>> +static freelist_idx_t master_list_8[8]; >>>>>> +static freelist_idx_t master_list_16[16]; >>>>>> +static freelist_idx_t master_list_32[32]; >>>>>> +static freelist_idx_t master_list_64[64]; >>>>>> +static freelist_idx_t master_list_128[128]; >>>>>> +static freelist_idx_t master_list_256[256]; >>>>>> +static struct m_list { >>>>>> + size_t count; >>>>>> + freelist_idx_t *list; >>>>>> +} master_lists[] = { >>>>>> + { ARRAY_SIZE(master_list_2), master_list_2 }, >>>>>> + { ARRAY_SIZE(master_list_4), master_list_4 }, >>>>>> + { ARRAY_SIZE(master_list_8), master_list_8 }, >>>>>> + { ARRAY_SIZE(master_list_16), master_list_16 }, >>>>>> + { ARRAY_SIZE(master_list_32), master_list_32 }, >>>>>> + { ARRAY_SIZE(master_list_64), master_list_64 }, >>>>>> + { ARRAY_SIZE(master_list_128), master_list_128 }, >>>>>> + { ARRAY_SIZE(master_list_256), master_list_256 }, >>>>>> +}; >>>> >>>> >>>> static const struct m_list? >>>> > -- 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