From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Sat, 24 Jun 2017 10:11:11 +0100 From: Russell King - ARM Linux Message-ID: <20170624091110.GX4902@n2100.armlinux.org.uk> References: <1498251600-132458-1-git-send-email-keescook@chromium.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1498251600-132458-1-git-send-email-keescook@chromium.org> Sender: Russell King - ARM Linux Subject: [kernel-hardening] Re: [PATCH v2 0/5] Use ELF_ET_DYN_BASE only for PIE List-Archive: List-Post: To: Kees Cook Cc: Andrew Morton , Rik van Riel , Ard Biesheuvel , Daniel Micay , Qualys Security Advisory , Catalin Marinas , Will Deacon , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , Martin Schwidefsky , Heiko Carstens , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , x86@kernel.org, Alexander Viro , Pratyush Anand , James Hogan , Dmitry Safonov , Grzegorz Andrejczuk , Masahiro Yamada , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-fsdevel@vger.kernel.org, kernel-hardening@lists.openwall.com List-ID: On Fri, Jun 23, 2017 at 01:59:55PM -0700, Kees Cook wrote: > This is v2 (to refresh the 5 patches in -mm) for moving ELF_ET_DYN_BASE > safely lower. Changes are clarifications in the commit logs (suggested > by mpe), a compat think-o fix for arm64 (thanks to Ard), and to add > Rik and mpe's Acks. > > Quoting patch 1/5: > > The ELF_ET_DYN_BASE position was originally intended to keep loaders > away from ET_EXEC binaries. (For example, running "/lib/ld-linux.so.2 > /bin/cat" might cause the subsequent load of /bin/cat into where the > loader had been loaded.) With the advent of PIE (ET_DYN binaries with > an INTERP Program Header), ELF_ET_DYN_BASE continued to be used since > the kernel was only looking at ET_DYN. However, since ELF_ET_DYN_BASE > is traditionally set at the top 1/3rd of the TASK_SIZE, a substantial > portion of the address space is unused. With existing kernels on ARM: 00010000-00017000 r-xp 00000000 08:01 270810 /bin/cat 00026000-00027000 r--p 00006000 08:01 270810 /bin/cat 00027000-00028000 rw-p 00007000 08:01 270810 /bin/cat 7f661000-7f679000 r-xp 00000000 08:01 281659 /lib/arm-linux-gnueabihf/ld-2.23.so 7f688000-7f689000 r--p 00017000 08:01 281659 /lib/arm-linux-gnueabihf/ld-2.23.so 7f689000-7f68a000 rw-p 00018000 08:01 281659 /lib/arm-linux-gnueabihf/ld-2.23.so If the loader is loaded at 4MB, this means the size of an ET_EXEC program is limited to less than 4MB - and distros aren't yet building everything as PIE on ARM. -- RMK's Patch system: http://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up according to speedtest.net.