From: John David Anglin <danglin@gcc.gnu.org>
Date: Sat, 15 Jul 2017 16:40:13 +0000 (-0400)
Subject: Fix guard alignment in allocate_stack when stack grows up.
X-Git-Tag: glibc-2.26~91
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=075385f98af239ff5807a5c6ed17fec51e048454;p=thirdparty%2Fglibc.git

Fix guard alignment in allocate_stack when stack grows up.
---

diff --git a/ChangeLog b/ChangeLog
index b6befe23294..41c050e0a34 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,8 @@
 2017-07-15  John David Anglin  <danglin@gcc.gnu.org>
 
+	* nptl/allocatestack.c (allocate_stack): Align old and new guard
+	addresses to page boundaries when the stack grows up.
+
 	* sysdeps/hppa/math-tests.h: New.
 
 2017-07-14  DJ Delorie  <dj@redhat.com>
diff --git a/nptl/allocatestack.c b/nptl/allocatestack.c
index ec7d42e027b..ce2e24af951 100644
--- a/nptl/allocatestack.c
+++ b/nptl/allocatestack.c
@@ -697,8 +697,14 @@ allocate_stack (const struct pthread_attr *attr, struct pthread **pdp,
 			prot) != 0)
 	    goto mprot_error;
 #elif _STACK_GROWS_UP
-	  if (__mprotect ((char *) pd - pd->guardsize,
-			pd->guardsize - guardsize, prot) != 0)
+         char *new_guard = (char *)(((uintptr_t) pd - guardsize)
+                                    & ~pagesize_m1);
+         char *old_guard = (char *)(((uintptr_t) pd - pd->guardsize)
+                                    & ~pagesize_m1);
+         /* The guard size difference might be > 0, but once rounded
+            to the nearest page the size difference might be zero.  */
+         if (new_guard > old_guard
+             && mprotect (old_guard, new_guard - old_guard, prot) != 0)
 	    goto mprot_error;
 #endif