From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756154AbbKDAEO (ORCPT ); Tue, 3 Nov 2015 19:04:14 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:53599 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756118AbbKDAEM (ORCPT ); Tue, 3 Nov 2015 19:04:12 -0500 Date: Tue, 3 Nov 2015 16:04:10 -0800 From: Andrew Morton To: Daniel Cashman Cc: linux-kernel@vger.kernel.org, linux@arm.linux.org.uk, keescook@chromium.org, mingo@kernel.org, linux-arm-kernel@lists.infradead.org, corbet@lwn.net, dzickus@redhat.com, ebiederm@xmission.com, xypron.glpk@gmx.de, jpoimboe@redhat.com, kirill.shutemov@linux.intel.com, n-horiguchi@ah.jp.nec.com, aarcange@redhat.com, mgorman@suse.de, tglx@linutronix.de, rientjes@google.com, linux-mm@kvack.org, linux-doc@vger.kernel.org, salyzyn@android.com, jeffv@google.com, nnk@google.com, dcashman Subject: Re: [PATCH v2 1/2] mm: mmap: Add new /proc tunable for mmap_base ASLR. Message-Id: <20151103160410.34bbebc805c17d2f41150a19@linux-foundation.org> In-Reply-To: <1446574204-15567-1-git-send-email-dcashman@android.com> References: <1446574204-15567-1-git-send-email-dcashman@android.com> X-Mailer: Sylpheed 3.4.1 (GTK+ 2.24.23; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 3 Nov 2015 10:10:03 -0800 Daniel Cashman wrote: > ASLR currently only uses 8 bits to generate the random offset for the > mmap base address on 32 bit architectures. This value was chosen to > prevent a poorly chosen value from dividing the address space in such > a way as to prevent large allocations. This may not be an issue on all > platforms. Allow the specification of a minimum number of bits so that > platforms desiring greater ASLR protection may determine where to place > the trade-off. Can we please include a very good description of the motivation for this change? What is inadequate about the current code, what value does the enhancement have to our users, what real-world problems are being solved, etc. Because all we have at present is "greater ASLR protection", which doesn't really tell anyone anything.