Commit abb79a56 authored Jul 10, 2017 by Kees Cook Committed by Greg Kroah-Hartman Jul 21, 2017

arm: move ELF_ET_DYN_BASE to 4MB

commit 6a9af90a3bcde217a1c053e135f5f43e5d5fafbd upstream.

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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 63c2f8f8

arch/arm/include/asm/elf.h

+2 −6

Original line number	Diff line number	Diff line
		@@ -112,12 +112,8 @@ int dump_task_regs(struct task_struct t, elf_gregset_t elfregs);
		#define CORE_DUMP_USE_REGSET
		#define ELF_EXEC_PAGESIZE 4096

		/* This is the location that an ET_DYN program is loaded if exec'ed. Typical
		use of this is to invoke "./ld.so someprog" to test out a new version of
		the loader. We need to make sure that it is out of the way of the program
		that it will "exec", and that there is sufficient room for the brk. */

		#define ELF_ET_DYN_BASE (TASK_SIZE / 3 * 2)
		/* This is the base location for PIE (ET_DYN with INTERP) loads. */
		#define ELF_ET_DYN_BASE 0x400000UL

		/* When the program starts, a1 contains a pointer to a function to be
		registered with atexit, as per the SVR4 ABI. A value of 0 means we