arm64: ASLR: Don't randomise text when randomise_va_space == 0

When user asks to turn off ASLR by writing "0" to
/proc/sys/kernel/randomize_va_space there should not be
any randomization to mmap base, stack, VDSO, libs, text and heap

Currently arm64 violates this behavior by randomising text.
Fix this by defining a constant ELF_ET_DYN_BASE. The randomisation of
mm->mmap_base is done by setup_new_exec -> arch_pick_mmap_layout ->
mmap_base -> mmap_rnd.
Signed-off-by: NArun Chandran <achandran@mvista.com>
Signed-off-by: NCatalin Marinas <catalin.marinas@arm.com>

arch/arm64/Kconfig

 config ARM64
 	def_bool y
+	select ARCH_BINFMT_ELF_RANDOMIZE_PIE
 	select ARCH_HAS_ATOMIC64_DEC_IF_POSITIVE
 	select ARCH_HAS_SG_CHAIN
 	select ARCH_HAS_TICK_BROADCAST if GENERIC_CLOCKEVENTS_BROADCAST

arch/arm64/include/asm/elf.h

@@ -126,7 +126,7 @@ typedef struct user_fpsimd_state elf_fpregset_t;
  * that it will "exec", and that there is sufficient room for the brk.
  */
 extern unsigned long randomize_et_dyn(unsigned long base);
-#define ELF_ET_DYN_BASE	(randomize_et_dyn(2 * TASK_SIZE_64 / 3))
+#define ELF_ET_DYN_BASE	(2 * TASK_SIZE_64 / 3)
 
 /*
  * When the program starts, a1 contains a pointer to a function to be
@@ -169,7 +169,7 @@ extern unsigned long arch_randomize_brk(struct mm_struct *mm);
 #define COMPAT_ELF_PLATFORM		("v8l")
 #endif
 
-#define COMPAT_ELF_ET_DYN_BASE		(randomize_et_dyn(2 * TASK_SIZE_32 / 3))
+#define COMPAT_ELF_ET_DYN_BASE		(2 * TASK_SIZE_32 / 3)
 
 /* AArch32 registers. */
 #define COMPAT_ELF_NGREG		18

arch/arm64/kernel/process.c

@@ -378,8 +378,3 @@ unsigned long arch_randomize_brk(struct mm_struct *mm)
 {
 	return randomize_base(mm->brk);
 }
-
-unsigned long randomize_et_dyn(unsigned long base)
-{
-	return randomize_base(base);
-}