s390: redefine randomize_et_dyn for ELF_ET_DYN_BASE

commit c6f5b001 upstream.

In preparation for moving ET_DYN randomization into the ELF loader (which
requires a static ELF_ET_DYN_BASE), this redefines s390's existing ET_DYN
randomization in a call to arch_mmap_rnd(). This refactoring results in
the same ET_DYN randomization on s390.
Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>

arch/s390/include/asm/elf.h

@@ -161,10 +161,12 @@ extern unsigned int vdso_enabled;
 /* 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.  */
-
+   that it will "exec", and that there is sufficient room for the brk. 64-bit
+   tasks are aligned to 4GB. */
 extern unsigned long randomize_et_dyn(void);
-#define ELF_ET_DYN_BASE		randomize_et_dyn()
+#define ELF_ET_DYN_BASE (randomize_et_dyn() + (is_32bit_task() ? \
+				(STACK_TOP / 3 * 2) : \
+				(STACK_TOP / 3 * 2) & ~((1UL << 32) - 1)))
 
 /* This yields a mask that user programs can use to figure out what
    instruction set this CPU supports. */

arch/s390/mm/mmap.c

@@ -179,17 +179,10 @@ arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
 
 unsigned long randomize_et_dyn(void)
 {
-	unsigned long base;
-
-	base = STACK_TOP / 3 * 2;
-	if (!is_32bit_task())
-		/* Align to 4GB */
-		base &= ~((1UL << 32) - 1);
-
 	if (current->flags & PF_RANDOMIZE)
-		base += arch_mmap_rnd();
+		return arch_mmap_rnd();
 
-	return base;
+	return 0UL;
 }
 
 #ifndef CONFIG_64BIT