[PATCH] x86_64: Fix stack/mmap randomization for compat tasks

ia32_setup_arg_pages would ignore the passed in random stack top
and use its own static value.

Now it uses the 8bit of randomness native i386 would use too.

This indirectly fixes mmap randomization for 32bit processes too,
which depends on the stack randomization.

Should also give slightly better virtual cache colouring and
possibly better performance with HyperThreading.
Signed-off-by: Andi Kleen <ak@suse.de>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/x86_64/ia32/ia32_binfmt.c

@@ -339,7 +339,7 @@ int ia32_setup_arg_pages(struct linux_binprm *bprm, unsigned long stack_top,
 	struct mm_struct *mm = current->mm;
 	int i, ret;
 
-	stack_base = IA32_STACK_TOP - MAX_ARG_PAGES * PAGE_SIZE;
+	stack_base = stack_top - MAX_ARG_PAGES * PAGE_SIZE;
 	mm->arg_start = bprm->p + stack_base;
 
 	bprm->p += stack_base;
@@ -357,7 +357,7 @@ int ia32_setup_arg_pages(struct linux_binprm *bprm, unsigned long stack_top,
 	{
 		mpnt->vm_mm = mm;
 		mpnt->vm_start = PAGE_MASK & (unsigned long) bprm->p;
-		mpnt->vm_end = IA32_STACK_TOP;
+		mpnt->vm_end = stack_top;
 		if (executable_stack == EXSTACK_ENABLE_X)
 			mpnt->vm_flags = VM_STACK_FLAGS |  VM_EXEC;
 		else if (executable_stack == EXSTACK_DISABLE_X)

include/asm-x86_64/elf.h

@@ -159,7 +159,7 @@ extern int dump_task_fpu (struct task_struct *, elf_fpregset_t *);
 #define ELF_CORE_COPY_FPREGS(tsk, elf_fpregs) dump_task_fpu(tsk, elf_fpregs)
 
 /* 1GB for 64bit, 8MB for 32bit */
-#define STACK_RND_MASK (is_compat_task() ? 0x7ff : 0x3fffff)
+#define STACK_RND_MASK (test_thread_flag(TIF_IA32) ? 0x7ff : 0x3fffff)
 
 #endif