[PATCH v5 01/14] mm, fs: Move randomize_stack_top from fs to mm

[Alexandre Ghiti <alex@ghiti.fr>]

This preparatory commit moves this function so that further introduction
of generic topdown mmap layout is contained only in mm/util.c.

Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
Acked-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
---
 fs/binfmt_elf.c    | 20 --------------------
 include/linux/mm.h |  2 ++
 mm/util.c          | 22 ++++++++++++++++++++++
 3 files changed, 24 insertions(+), 20 deletions(-)

diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index d4e11b2e04f6..cec3b4146440 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -670,26 +670,6 @@ static unsigned long load_elf_interp(struct elfhdr *interp_elf_ex,
  * libraries.  There is no binary dependent code anywhere else.
  */
 
-#ifndef STACK_RND_MASK
-#define STACK_RND_MASK (0x7ff >> (PAGE_SHIFT - 12))	/* 8MB of VA */
-#endif
-
-static unsigned long randomize_stack_top(unsigned long stack_top)
-{
-	unsigned long random_variable = 0;
-
-	if (current->flags & PF_RANDOMIZE) {
-		random_variable = get_random_long();
-		random_variable &= STACK_RND_MASK;
-		random_variable <<= PAGE_SHIFT;
-	}
-#ifdef CONFIG_STACK_GROWSUP
-	return PAGE_ALIGN(stack_top) + random_variable;
-#else
-	return PAGE_ALIGN(stack_top) - random_variable;
-#endif
-}
-
 static int load_elf_binary(struct linux_binprm *bprm)
 {
 	struct file *interpreter = NULL; /* to shut gcc up */
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 0334ca97c584..ae0e5d241eb8 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2351,6 +2351,8 @@ extern int install_special_mapping(struct mm_struct *mm,
 				   unsigned long addr, unsigned long len,
 				   unsigned long flags, struct page **pages);
 
+unsigned long randomize_stack_top(unsigned long stack_top);
+
 extern unsigned long get_unmapped_area(struct file *, unsigned long, unsigned long, unsigned long, unsigned long);
 
 extern unsigned long mmap_region(struct file *file, unsigned long addr,
diff --git a/mm/util.c b/mm/util.c
index e6351a80f248..15a4fb0f5473 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -16,6 +16,8 @@
 #include <linux/hugetlb.h>
 #include <linux/vmalloc.h>
 #include <linux/userfaultfd_k.h>
+#include <linux/elf.h>
+#include <linux/random.h>
 
 #include <linux/uaccess.h>
 
@@ -293,6 +295,26 @@ int vma_is_stack_for_current(struct vm_area_struct *vma)
 	return (vma->vm_start <= KSTK_ESP(t) && vma->vm_end >= KSTK_ESP(t));
 }
 
+#ifndef STACK_RND_MASK
+#define STACK_RND_MASK (0x7ff >> (PAGE_SHIFT - 12))     /* 8MB of VA */
+#endif
+
+unsigned long randomize_stack_top(unsigned long stack_top)
+{
+	unsigned long random_variable = 0;
+
+	if (current->flags & PF_RANDOMIZE) {
+		random_variable = get_random_long();
+		random_variable &= STACK_RND_MASK;
+		random_variable <<= PAGE_SHIFT;
+	}
+#ifdef CONFIG_STACK_GROWSUP
+	return PAGE_ALIGN(stack_top) + random_variable;
+#else
+	return PAGE_ALIGN(stack_top) - random_variable;
+#endif
+}
+
 #if defined(CONFIG_MMU) && !defined(HAVE_ARCH_PICK_MMAP_LAYOUT)
 void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
 {
-- 
2.20.1