NOMMU: Teach kobjsize() about VMA regions.

Now that we no longer use compound pages for all large allocations,
kobjsize() actively breaks things like binfmt_flat by always handing
back PAGE_SIZE for mmap'ed regions. Fix this up by looking up the
VMA region for non-compounds.

Ideally binfmt_flat wants to get rid of kobjsize() completely, but
this is an incremental step.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>
Signed-off-by: David Howells <dhowells@redhat.com>
Tested-by: Mike Frysinger <vapier.adi@gmail.com>

1 files changed, 14 insertions, 0 deletions

diff --git a/mm/nommu.c b/mm/nommu.c
index a6e8ccfbd400..60ed8375c986 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -149,6 +149,20 @@ unsigned int kobjsize(const void *objp)
                 return ksize(objp);
 
         /*
+         * If it's not a compound page, see if we have a matching VMA
+         * region. This test is intentionally done in reverse order,
+         * so if there's no VMA, we still fall through and hand back
+         * PAGE_SIZE for 0-order pages.
+         */
+        if (!PageCompound(page)) {
+                struct vm_area_struct *vma;
+
+                vma = find_vma(current->mm, (unsigned long)objp);
+                if (vma)
+                        return vma->vm_end - vma->vm_start;
+        }
+
+        /*
          * The ksize() function is only guaranteed to work for pointers
          * returned by kmalloc(). So handle arbitrary pointers here.
          */