From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 77990C77B73 for ; Sun, 16 Apr 2023 11:55:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230126AbjDPLz5 (ORCPT ); Sun, 16 Apr 2023 07:55:57 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33380 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230036AbjDPLzz (ORCPT ); Sun, 16 Apr 2023 07:55:55 -0400 Received: from mail-pf1-x42d.google.com (mail-pf1-x42d.google.com [IPv6:2607:f8b0:4864:20::42d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9330F3A99 for ; Sun, 16 Apr 2023 04:55:51 -0700 (PDT) Received: by mail-pf1-x42d.google.com with SMTP id d2e1a72fcca58-63b5ce4f069so927362b3a.1 for ; Sun, 16 Apr 2023 04:55:51 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20221208; t=1681646150; x=1684238150; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=Y8KZ3r9X7m+frzkUk71abgu3pE7RU14Dc/ipsaHwcko=; b=XoMq0EVWI3nRgXwtqQFUyUpQLhUcLHer4Yo9nSw6D+lKunzd9B3jNIK72QJ5//v3MC AHLPlQr7B2ZErB4zHnCN8YstKDjk17SWcGzlw85VLT2hzPKugGKLPvwcZDj/4zN2lKdx RVIj5GTGwR1YeLaXGSi++0qJEwa0FGPg3JqdT7SXfnKqe6b6/iYHz549hUmsB6NGpGA7 K+0l2TtsYgNhBIuloGc5UyXr6vhrBSw/fpsF5BHjsK0CnpnAP5++BYMfp9SW+B3HcVTz X3N46a5zN4P1zIHLZfD6W13NuoCSAS6kC26fi0/KwwAKMMF3srCAr8Ld3MEv2h0XgJzT HRrA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1681646150; x=1684238150; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=Y8KZ3r9X7m+frzkUk71abgu3pE7RU14Dc/ipsaHwcko=; b=Zn7GnEUrxEZGEGpGtrgPI5mI/xWeVMsLikxKW1JANaC+drrhWigMpeM6ISarCIJ1m2 W4t+lBVL7pwHPGtM2om5wt4rYFbLRxdB2SblUaX8SBJK4+R1qGsGga3AyYvr3RsP/oVy F9DsObxvxWuyG+MJR1zuL6WAaTC2/urxBep3MCS4B8YYQtSF6ZVJBEgmgK135mizIgWw zyX/u80q/cdraR2YIsLbi3JFnGTgNNjUHdSdUZdD6ASAhDrilyz1SGrmboNEX4xVXxoL faC48XbQEkpX+FiBN9BgyfGJpWcI1GnEvr5GM8ha1x15qarLBu70fxFRLSt4PyGOktoT WDCA== X-Gm-Message-State: AAQBX9fxHzaLotiH9vnTIp7gPjNrmV7OtHFqvQt7470w4dAGrzZL0aXP bTsCN/MwQ6sYBItmpQqJ5D00+QYIfct2mYr4 X-Google-Smtp-Source: AKy350ZwTAHDISNb23JdS5FOQLwjDaG3jTcMflOFrRkYG0ua5qimsZYO+gjQ3z/Y30C7TbgNhsjLcw== X-Received: by 2002:a05:6a00:1ac7:b0:63b:5f78:d6e1 with SMTP id f7-20020a056a001ac700b0063b5f78d6e1mr13277000pfv.16.1681646150178; Sun, 16 Apr 2023 04:55:50 -0700 (PDT) Received: from hyeyoo ([211.108.101.96]) by smtp.gmail.com with ESMTPSA id c2-20020aa78802000000b0063b7a0b9cc5sm2555924pfo.186.2023.04.16.04.55.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 16 Apr 2023 04:55:49 -0700 (PDT) Date: Sun, 16 Apr 2023 20:55:39 +0900 From: Hyeonggon Yoo <42.hyeyoo@gmail.com> To: david.keisarschm@mail.huji.ac.il Cc: linux-kernel@vger.kernel.org, Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Andrew Morton , Vlastimil Babka , Roman Gushchin , Jason@zx2c4.com, linux-mm@kvack.org, ilay.bahat1@gmail.com, aksecurity@gmail.com Subject: Re: [PATCH v5 2/3] Replace invocation of weak PRNG Message-ID: References: <20230415173650.5458-1-david.keisarschm@mail.huji.ac.il> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230415173650.5458-1-david.keisarschm@mail.huji.ac.il> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Apr 15, 2023 at 08:36:49PM +0300, david.keisarschm@mail.huji.ac.il wrote: > From: David Keisar Schmidt > > The Slab allocator randomization inside slab_common.c > uses the prandom_u32 PRNG. That was added to prevent attackers to obtain > information on the heap state. > > However, this PRNG turned out to be weak, as noted in commit c51f8f88d705 > To fix it, we have changed the invocation of prandom_u32_state to get_random_u32 > to ensure the PRNG is strong. > > Since a modulo operation is applied right after that, > in the Fisher-Yates shuffle, we used get_random_u32_below, to achieve uniformity. > > Signed-off-by: David Keisar Schmidt > --- same comment for the subject line. > > This fifth series changes only the arch/x86/mm/kaslr patch. > > Changes since v3: > * edited commit message. > > Changes since v2: > > * replaced instances of get_random_u32 with get_random_u32_below > in mm/slab_common.c. > > mm/slab_common.c | 11 +++-------- > 1 file changed, 3 insertions(+), 8 deletions(-) > > diff --git a/mm/slab_common.c b/mm/slab_common.c > index bf4e777cf..361da2191 100644 > --- a/mm/slab_common.c > +++ b/mm/slab_common.c > @@ -1146,7 +1146,7 @@ EXPORT_SYMBOL(kmalloc_large_node); > > #ifdef CONFIG_SLAB_FREELIST_RANDOM > /* Randomize a generic freelist */ > -static void freelist_randomize(struct rnd_state *state, unsigned int *list, > +static void freelist_randomize(unsigned int *list, > unsigned int count) > { > unsigned int rand; > @@ -1157,8 +1157,7 @@ static void freelist_randomize(struct rnd_state *state, unsigned int *list, > > /* Fisher-Yates shuffle */ > for (i = count - 1; i > 0; i--) { > - rand = prandom_u32_state(state); > - rand %= (i + 1); > + rand = get_random_u32_below(i+1); same here. otherwise looks good to me. > swap(list[i], list[rand]); > } > } > @@ -1167,7 +1166,6 @@ static void freelist_randomize(struct rnd_state *state, unsigned int *list, > int cache_random_seq_create(struct kmem_cache *cachep, unsigned int count, > gfp_t gfp) > { > - struct rnd_state state; > > if (count < 2 || cachep->random_seq) > return 0; > @@ -1176,10 +1174,7 @@ int cache_random_seq_create(struct kmem_cache *cachep, unsigned int count, > if (!cachep->random_seq) > return -ENOMEM; > > - /* Get best entropy at this stage of boot */ > - prandom_seed_state(&state, get_random_long()); > - > - freelist_randomize(&state, cachep->random_seq, count); > + freelist_randomize(cachep->random_seq, count); > return 0; > } > > -- > 2.37.3 >