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.
