From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Message-id: <550C07AE.8030708@samsung.com> Date: Fri, 20 Mar 2015 14:42:38 +0300 From: Andrey Ryabinin MIME-version: 1.0 To: Yury Gribov Cc: Russell King , Kees Cook , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Maria Guseva , stable@vger.kernel.org Subject: Re: [PATCH] arm: fix integer overflow in ELF_ET_DYN_BASE References: <1426849972-19606-1-git-send-email-a.ryabinin@samsung.com> <550C0503.3000207@samsung.com> In-reply-to: <550C0503.3000207@samsung.com> Content-type: text/plain; charset=windows-1252 Content-transfer-encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: On 03/20/2015 02:31 PM, Yury Gribov wrote: > On 03/20/2015 02:12 PM, Andrey Ryabinin wrote: >> Usually ELF_ET_DYN_BASE is 2/3 of TASK_SIZE. With 3G/1G user/kernel >> split this is not so, because 2*TASK_SIZE overflows 32 bits, >> so the actual value of ELF_ET_DYN_BASE is: >> (2 * TASK_SIZE / 3) = 0x2a000000 > > AFAIK on most platforms (e.g. Intel) that's (TASK_SIZE / 3 * 2) so ARM is kind of special here. > >> >> When ASLR is disabled PIE binaries will load at ELF_ET_DYN_BASE address. >> On 32bit platforms AddressSanitzer uses addresses [0x20000000 - 0x40000000] >> for shadow memory [1]. So ASan doesn't work for PIE binaries when ASLR disabled >> as it fails to map shadow memory. >> Also after Kees's 'split ET_DYN ASLR from mmap ASLR' patchset PIE binaries >> has a high chance of loading somewhere in between [0x2a000000 - 0x40000000] >> even if ASLR enabled. This makes ASan with PIE absolutely incompatible. >> >> Fix overflow by dividing TASK_SIZE prior to multiplying. >> After this patch ELF_ET_DYN_BASE equals to (for CONFIG_VMSPLIT_3G=y): >> (TASK_SIZE / 3 * 2) = 0x7f555554 >> >> [1] https://code.google.com/p/address-sanitizer/wiki/AddressSanitizerAlgorithm#Mapping > > Perhaps we should fix other platforms as well? > Seems only avr32 and cris platforms have the same problem. All other 32bit platforms where ELF_ET_DYB_BASE = (2 * TASK_SIZE / 3) have TASK_SIZE < 2G, so there is no overflow.