RFP prot support: disallow mprotect() on manyprots mappings

From: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>

For now we (I and Hugh) have found no agreement on which behavior to implement
here. So, at least as a stop-gap, return an error here.

Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
---

 mm/mprotect.c |    7 +++++++
 1 files changed, 7 insertions(+), 0 deletions(-)

diff --git a/mm/mprotect.c b/mm/mprotect.c
index 638edab..401ae11 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -240,6 +240,13 @@ sys_mprotect(unsigned long start, size_t
 	error = -ENOMEM;
 	if (!vma)
 		goto out;
+
+	/* If a need is felt, an appropriate behaviour may be implemented for
+	 * this case. We haven't agreed yet on which behavior is appropriate. */
+	error = -EACCES;
+	if (vma->vm_flags & VM_MANYPROTS)
+		goto out;
+
 	if (unlikely(grows & PROT_GROWSDOWN)) {
 		if (vma->vm_start >= end)
 			goto out;