3 files changed, 38 insertions, 2 deletions

diff --git a/fs/exec.c b/fs/exec.c
index e6e94c626c2c..9badbc0bfb1d 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -242,9 +242,10 @@ static int __bprm_mm_init(struct linux_binprm *bprm)
          * use STACK_TOP because that can depend on attributes which aren't
          * configured yet.
          */
+        BUG_ON(VM_STACK_FLAGS & VM_STACK_INCOMPLETE_SETUP);
         vma->vm_end = STACK_TOP_MAX;
         vma->vm_start = vma->vm_end - PAGE_SIZE;
-        vma->vm_flags = VM_STACK_FLAGS;
+        vma->vm_flags = VM_STACK_FLAGS | VM_STACK_INCOMPLETE_SETUP;
         vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
         INIT_LIST_HEAD(&vma->anon_vma_chain);
         err = insert_vm_struct(mm, vma);
@@ -616,6 +617,7 @@ int setup_arg_pages(struct linux_binprm *bprm,
         else if (executable_stack == EXSTACK_DISABLE_X)
                 vm_flags &= ~VM_EXEC;
         vm_flags |= mm->def_flags;
+        vm_flags |= VM_STACK_INCOMPLETE_SETUP;
 
         ret = mprotect_fixup(vma, &prev, vma->vm_start, vma->vm_end,
                         vm_flags);
@@ -630,6 +632,9 @@ int setup_arg_pages(struct linux_binprm *bprm,
                         goto out_unlock;
         }
 
+        /* mprotect_fixup is overkill to remove the temporary stack flags */
+        vma->vm_flags &= ~VM_STACK_INCOMPLETE_SETUP;
+
         stack_expand = 131072UL; /* randomly 32*4k (or 2*64k) pages */
         stack_size = vma->vm_end - vma->vm_start;
         /*
diff --git a/include/linux/mm.h b/include/linux/mm.h
index fb19bb92b809..98ea5bab963e 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -106,6 +106,9 @@ extern unsigned int kobjsize(const void *objp);
 #define VM_PFN_AT_MMAP  0x40000000      /* PFNMAP vma that is fully mapped at mmap time */
 #define VM_MERGEABLE    0x80000000      /* KSM may merge identical pages */
 
+/* Bits set in the VMA until the stack is in its final location */
+#define VM_STACK_INCOMPLETE_SETUP       (VM_RAND_READ | VM_SEQ_READ)
+
 #ifndef VM_STACK_DEFAULT_FLAGS          /* arch can override this */
 #define VM_STACK_DEFAULT_FLAGS VM_DATA_DEFAULT_FLAGS
 #endif
diff --git a/mm/rmap.c b/mm/rmap.c
index b5c320f7d0a5..38a336e2eea1 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1131,6 +1131,20 @@ static int try_to_unmap_cluster(unsigned long cursor, unsigned int *mapcount,
         return ret;
 }
 
+static bool is_vma_temporary_stack(struct vm_area_struct *vma)
+{
+        int maybe_stack = vma->vm_flags & (VM_GROWSDOWN | VM_GROWSUP);
+
+        if (!maybe_stack)
+                return false;
+
+        if ((vma->vm_flags & VM_STACK_INCOMPLETE_SETUP) ==
+                                                VM_STACK_INCOMPLETE_SETUP)
+                return true;
+
+        return false;
+}
+
 /**
  * try_to_unmap_anon - unmap or unlock anonymous page using the object-based
  * rmap method
@@ -1159,7 +1173,21 @@ static int try_to_unmap_anon(struct page *page, enum ttu_flags flags)
 
         list_for_each_entry(avc, &anon_vma->head, same_anon_vma) {
                 struct vm_area_struct *vma = avc->vma;
-                unsigned long address = vma_address(page, vma);
+                unsigned long address;
+
+                /*
+                 * During exec, a temporary VMA is setup and later moved.
+                 * The VMA is moved under the anon_vma lock but not the
+                 * page tables leading to a race where migration cannot
+                 * find the migration ptes. Rather than increasing the
+                 * locking requirements of exec(), migration skips
+                 * temporary VMAs until after exec() completes.
+                 */
+                if (PAGE_MIGRATION && (flags & TTU_MIGRATION) &&
+                                is_vma_temporary_stack(vma))
+                        continue;
+
+                address = vma_address(page, vma);
                 if (address == -EFAULT)
                         continue;
                 ret = try_to_unmap_one(page, vma, address, flags);