arm: move ELF_ET_DYN_BASE to 4MB
authorKees Cook <keescook@chromium.org>
Mon, 10 Jul 2017 22:52:40 +0000 (15:52 -0700)
committerLinus Torvalds <torvalds@linux-foundation.org>
Mon, 10 Jul 2017 23:32:36 +0000 (16:32 -0700)
commit6a9af90a3bcde217a1c053e135f5f43e5d5fafbd
tree65fcf0d5e20635e3ed946d5b80a8dc16351fc04f
parenteab09532d40090698b05a07c1c87f39fdbc5fab5
arm: move ELF_ET_DYN_BASE to 4MB

Now that explicitly executed loaders are loaded in the mmap region, we
have more freedom to decide where we position PIE binaries in the
address space to avoid possible collisions with mmap or stack regions.

4MB is chosen here mainly to have parity with x86, where this is the
traditional minimum load location, likely to avoid historically
requiring a 4MB page table entry when only a portion of the first 4MB
would be used (since the NULL address is avoided).

For ARM the position could be 0x8000, the standard ET_EXEC load address,
but that is needlessly close to the NULL address, and anyone running PIE
on 32-bit ARM will have an MMU, so the tight mapping is not needed.

Link: http://lkml.kernel.org/r/1498154792-49952-2-git-send-email-keescook@chromium.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: James Hogan <james.hogan@imgtec.com>
Cc: Pratyush Anand <panand@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Daniel Micay <danielmicay@gmail.com>
Cc: Dmitry Safonov <dsafonov@virtuozzo.com>
Cc: Grzegorz Andrejczuk <grzegorz.andrejczuk@intel.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Qualys Security Advisory <qsa@qualys.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
arch/arm/include/asm/elf.h