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Wed, 24 Jan 2024 08:08:29 -0800 (PST) Received: from www.outflux.net ([198.0.35.241]) by smtp.gmail.com with ESMTPSA id i10-20020a17090320ca00b001d737d51411sm6630106plb.227.2024.01.24.08.08.29 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 24 Jan 2024 08:08:29 -0800 (PST) Date: Wed, 24 Jan 2024 08:08:28 -0800 From: Kees Cook To: Yang Shi Cc: Ard Biesheuvel , Matthew Wilcox , Linux ARM , mail@horotw.com, linux-hardening@vger.kernel.org, Jakub Wilk , Salvatore Bonaccorso , Linux Memory Management List , William Kucharski Subject: Re: Limited/Broken functionality of ASLR for Libs >= 2MB Message-ID: <202401240808.F5659B75@keescook> References: <69fa6015256613ed10aee996e181ebd4@horotw.com> <87il3ur1ik.fsf@gentoo.org> <07c348caaf6b4c457ab4b452f53ed048@horotw.com> <202401231433.FB2D7FBD@keescook> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 2B6D8A0016 X-Stat-Signature: onsoduifb9uyqxza6k8j5pkthx1emqx3 X-Rspam-User: X-HE-Tag: 1706112510-968260 X-HE-Meta: U2FsdGVkX1/ojiJnT7aCXQngjayc577Rl5XgfmKL46vaYKM0+cFD9Vo97LoJ6/W0TS8V9CCQL1i4Qwtr9zKELvehsl/nvMBeEgFyUHyE+JrcGW0ZbM2Kl0aACP3INNa+q58Sn/BedrfVHPkeM8mTisdxLwX8uW+yKhcau41aTJwpD1FQUYNMozxDgcfz0bkuHfmmxpA/5yUV6SYmbO8f4ObDgcwnkZ3COEb8XJFVQJD+A4uQICTaQk8Msp+4B7/I/ZlUKSMtcU7K1ajwSqrkH1XoBw+RSi8WVn9LABDiupPU/9t7hFclA7yQPtpJQRDazyJr0Yme1Fwty4oKfSr3438y/LWuFd6zXe6ceu1NijbZrj0dyFLY92+khmfyCApYiKfLcgMJ8OJIFJgdnalTvDqgMjHQ8P0AEsLV3+eTS+87sdPC7NDvfr6Gc+KpqDl092mkIxZP78ckAYkwqBhpX/cs3why3LXRnAoSXXoxhH0NodYLb+qGS33xlCWlET7f07JU0sgVcadsOhPdI2eDaCPA0GicaloWNlA94Ne4Gnb8dEk/gER7HVtFcBVNyjU9ibHU02aK9lWZCC4N5A3qN7/uzdAsnjlSSGyzSCI6CvXucENvI8vqrAFchdwadTbDojS6UbMWi42PAWXixfoewlvHgIhcbMxv1E8IQF5FjLdKUM5yTAElSc8QSyg63X5yRwn6Dk9fhjqABj0ujCAd0Lfp0AOLcL6pVRGznZzGioaCQMScQUBM92DWnt2eCR+87tjlx5NDxPwIDyYqivePSdvp0m30e8zMHxIKMd6cNqH7M3nTA1zdR9oY/aMKXpDVR5DfmGoqvJt7A3PoJzEIsTN+ZS7SeT48hlM/8Sxasm5Z8SCvcGfhv1wE3IN7Ij+hQ0tOiiw8BZUWk4Gi2PppC19FsZRrQgPkeBeNiJKyn3R8ATJsaGkp/lqNiaMFA3AK5J5UVbNIB8YCRboNNyq 3D1VOiGA 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.005516, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Jan 23, 2024 at 05:04:22PM -0800, Yang Shi wrote: > On Tue, Jan 23, 2024 at 2:37 PM Kees Cook wrote: > > > > On Tue, Jan 16, 2024 at 09:09:45AM +0100, Ard Biesheuvel wrote: > > > (cc Kees, LAKML) > > > > > > https://lkml.kernel.org/r/69fa6015256613ed10aee996e181ebd4%40horotw.com > > > > > > On Mon, 15 Jan 2024 at 21:46, Matthew Wilcox wrote: > > > > > > > ... > > > > Yeah, I don't know either. Outside my scope of expertise. > > > > > > > > I received a suggestion off-list that we only do the PMD alignment on > > > > 64-bit, which seems quite reasonable to me. After all, I don't care > > > > about performance on 32-bit just as much as I don't care about security > > > > on 32-bit. > > > > > > > > > > For context, the culprit is > > > > > > commit 1854bc6e2420472676c5c90d3d6b15f6cd640e40 > > > Author: William Kucharski > > > Date: Sun Sep 22 08:43:15 2019 -0400 > > > > > > mm/readahead: Align file mappings for non-DAX > > > > > > When we have the opportunity to use PMDs to map a file, we want to follow > > > the same rules as DAX. > > > > > > Signed-off-by: William Kucharski > > > Signed-off-by: Matthew Wilcox (Oracle) > > > > > > which affects *all* 32-bit architectures not just i686. 32-bit ARM > > > user space is still being deployed widely, even on arm64 Chromebooks > > > running 64-bit kernels (at least up until recently) so unfortunately, > > > we're not quite at the point yet where we can just let it rot. > > > > Is this related at all to this thread as well? > > https://lore.kernel.org/lkml/20220809142457.4751229f@imladris.surriel.com/ > > Yes > > > > > Can we avoid this on 32-bit or at least not mislead userspace about the > > available entropy visible in /proc/sys/vm/mmap_rnd*_bits ? > > https://lore.kernel.org/linux-mm/20240118133504.2910955-1-shy828301@gmail.com/ > > This patch basically made thp_get_unmapped_area no-op on 32 bit. Ah-ha! Okay, thanks very much. I missed this landing. :) -- Kees Cook