[PATCH 1/4] arm: Reduce ELF_ET_DYN_BASE

From: Kees Cook
Date: Thu Jun 22 2017 - 14:07:10 EST

Now that explicitly executed loaders are loaded in the mmap region,
position PIE binaries lower in the address space to avoid possible
collisions with mmap or stack regions.

Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
arch/arm/include/asm/elf.h | 8 ++------
1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/arch/arm/include/asm/elf.h b/arch/arm/include/asm/elf.h
index d2315ffd8f12..f13ae153fb24 100644
--- a/arch/arm/include/asm/elf.h
+++ b/arch/arm/include/asm/elf.h
@@ -112,12 +112,8 @@ int dump_task_regs(struct task_struct *t, elf_gregset_t *elfregs);
#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