nommu: fix malloc performance by adding uninitialized flag

The NOMMU code currently clears all anonymous mmapped memory.  While this
is what we want in the default case, all memory allocation from userspace
under NOMMU has to go through this interface, including malloc() which is
allowed to return uninitialized memory.  This can easily be a significant
performance penalty.  So for constrained embedded systems were security is
irrelevant, allow people to avoid clearing memory unnecessarily.

This also alters the ELF-FDPIC binfmt such that it obtains uninitialised
memory for the brk and stack region.

Signed-off-by: Jie Zhang <jie.zhang@analog.com>
Signed-off-by: Robin Getz <rgetz@blackfin.uclinux.org>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Paul Mundt <lethal@linux-sh.org>
Acked-by: Greg Ungerer <gerg@snapgear.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 5 insertions, 3 deletions

diff --git a/mm/nommu.c b/mm/nommu.c
index 9876fa0c3ad3..8687973462bb 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -1143,9 +1143,6 @@ static int do_mmap_private(struct vm_area_struct *vma,
                 if (ret < rlen)
                         memset(base + ret, 0, rlen - ret);
 
-        } else {
-                /* if it's an anonymous mapping, then just clear it */
-                memset(base, 0, rlen);
         }
 
         return 0;
@@ -1343,6 +1340,11 @@ unsigned long do_mmap_pgoff(struct file *file,
                 goto error_just_free;
         add_nommu_region(region);
 
+        /* clear anonymous mappings that don't ask for uninitialized data */
+        if (!vma->vm_file && !(flags & MAP_UNINITIALIZED))
+                memset((void *)region->vm_start, 0,
+                       region->vm_end - region->vm_start);
+
         /* okay... we have a mapping; now we have to register it */
         result = vma->vm_start;