From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michal Hocko Subject: Re: [RFC PATCH v2 0/2] Randomization of address chosen by mmap. Date: Mon, 26 Mar 2018 10:46:50 +0200 Message-ID: <20180326084650.GC5652@dhcp22.suse.cz> References: <1521736598-12812-1-git-send-email-blackzert@gmail.com> <20180323124806.GA5624@bombadil.infradead.org> <651E0DB6-4507-4DA1-AD46-9C26ED9792A8@gmail.com> Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Return-path: Content-Disposition: inline In-Reply-To: <651E0DB6-4507-4DA1-AD46-9C26ED9792A8@gmail.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="utf-8" To: Ilya Smith Cc: Matthew Wilcox , rth@twiddle.net, ink@jurassic.park.msu.ru, mattst88@gmail.com, vgupta@synopsys.com, linux@armlinux.org.uk, tony.luck@intel.com, fenghua.yu@intel.com, ralf@linux-mips.org, jejb@parisc-linux.org, Helge Deller , benh@kernel.crashing.org, paulus@samba.org, mpe@ellerman.id.au, schwidefsky@de.ibm.com, heiko.carstens@de.ibm.com, ysato@users.sourceforge.jp, dalias@libc.org, davem@davemloft.net, tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com, x86@kernel.org, nyc@holomorphy.com, viro@zeniv.linux.org.uk, arnd@arndb.de, gregkh@linuxfoundation.org, deepa.kernel@gmail.com, Hugh Dickins , kstewart@linuxfoundation.org, pombredanne@nexb.com, Andrew Morton , steve.capper@arm.com, punit.agrawal@arm. On Fri 23-03-18 20:55:49, Ilya Smith wrote: > > > On 23 Mar 2018, at 15:48, Matthew Wilcox wrote: > > > > On Thu, Mar 22, 2018 at 07:36:36PM +0300, Ilya Smith wrote: > >> Current implementation doesn't randomize address returned by mmap. > >> All the entropy ends with choosing mmap_base_addr at the process > >> creation. After that mmap build very predictable layout of address > >> space. It allows to bypass ASLR in many cases. This patch make > >> randomization of address on any mmap call. > > > > Why should this be done in the kernel rather than libc? libc is perfectly > > capable of specifying random numbers in the first argument of mmap. > Well, there is following reasons: > 1. It should be done in any libc implementation, what is not possible IMO; Is this really so helpful? > 2. User mode is not that layer which should be responsible for choosing > random address or handling entropy; Why? > 3. Memory fragmentation is unpredictable in this case > > Off course user mode could use random ‘hint’ address, but kernel may > discard this address if it is occupied for example and allocate just before > closest vma. So this solution doesn’t give that much security like > randomization address inside kernel. The userspace can use the new MAP_FIXED_NOREPLACE to probe for the address range atomically and chose a different range on failure. -- Michal Hocko SUSE Labs