x86 get_unmapped_area: Access mmap_legacy_base through mm_struct member

This is the updated version of df54d6fa5427 ("x86 get_unmapped_area():
use proper mmap base for bottom-up direction") that only randomizes the
mmap base address once.

Signed-off-by: Radu Caragea <sinaelgl@gmail.com>
Reported-and-tested-by: Jeff Shorey <shoreyjeff@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Michel Lespinasse <walken@google.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Adrian Sendroiu <molecula2788@gmail.com>
Cc: Greg KH <greg@kroah.com>
Cc: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 6 insertions, 3 deletions

diff --git a/arch/x86/kernel/sys_x86_64.c b/arch/x86/kernel/sys_x86_64.c
index dbded5aedb81..30277e27431a 100644
--- a/arch/x86/kernel/sys_x86_64.c
+++ b/arch/x86/kernel/sys_x86_64.c
@@ -101,7 +101,7 @@ static void find_start_end(unsigned long flags, unsigned long *begin,
                                 *begin = new_begin;
                 }
         } else {
-                *begin = TASK_UNMAPPED_BASE;
+                *begin = current->mm->mmap_legacy_base;
                 *end = TASK_SIZE;
         }
 }
diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c
index 62c29a5bfe26..25e7e1372bb2 100644
--- a/arch/x86/mm/mmap.c
+++ b/arch/x86/mm/mmap.c
@@ -112,11 +112,13 @@ static unsigned long mmap_legacy_base(void)
  */
 void arch_pick_mmap_layout(struct mm_struct *mm)
 {
+        mm->mmap_legacy_base = mmap_legacy_base();
+        mm->mmap_base = mmap_base();
+
         if (mmap_is_legacy()) {
-                mm->mmap_base = mmap_legacy_base();
+                mm->mmap_base = mm->mmap_legacy_base;
                 mm->get_unmapped_area = arch_get_unmapped_area;
         } else {
-                mm->mmap_base = mmap_base();
                 mm->get_unmapped_area = arch_get_unmapped_area_topdown;
         }
 }
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index fb425aa16c01..faf4b7c1ad12 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -332,6 +332,7 @@ struct mm_struct {
                                 unsigned long pgoff, unsigned long flags);
 #endif
         unsigned long mmap_base;                /* base of mmap area */
+        unsigned long mmap_legacy_base;         /* base of mmap area in bottom-up allocations */
         unsigned long task_size;                /* size of task vm space */
         unsigned long highest_vm_end;           /* highest vma end address */
         pgd_t * pgd;