MFC - Fix libthread_xu's use of MAP_STACK. Guards not being setup properly.

diff --git a/lib/libthread_xu/thread/thr_init.c b/lib/libthread_xu/thread/thr_init.c
index 42723e6..1f0ad74 100644 (file)
--- a/lib/libthread_xu/thread/thr_init.c
+++ b/lib/libthread_xu/thread/thr_init.c
@@ -258,9 +258,10 @@ init_main_thread(struct pthread *thread)
         * red zone to protect the thread stack that is just beyond.
         */
        if (mmap(_usrstack - _thr_stack_initial -
-           _thr_guard_default, _thr_guard_default, 0, MAP_ANON,
-           -1, 0) == MAP_FAILED)
+               _thr_guard_default, _thr_guard_default,
+               0, MAP_ANON | MAP_FIXED, -1, 0) == MAP_FAILED) {
                PANIC("Cannot allocate red zone for initial thread");
+       }
 
        /*
         * Mark the stack as an application supplied stack so that it

diff --git a/lib/libthread_xu/thread/thr_stack.c b/lib/libthread_xu/thread/thr_stack.c
index 68af995..cae1267 100644 (file)
--- a/lib/libthread_xu/thread/thr_stack.c
+++ b/lib/libthread_xu/thread/thr_stack.c
@@ -190,9 +190,10 @@ _thr_stack_alloc(struct pthread_attr *attr)
        }
        else {
                /* Allocate a stack from usrstack. */
-               if (last_stack == NULL)
+               if (last_stack == NULL) {
                        last_stack = _usrstack - _thr_stack_initial -
-                           _thr_guard_default;
+                                    _thr_guard_default;
+               }
 
                /* Allocate a new stack. */
                stackaddr = last_stack - stacksize - guardsize;
@@ -209,19 +210,28 @@ _thr_stack_alloc(struct pthread_attr *attr)
                /* Release the lock before mmap'ing it. */
                THREAD_LIST_UNLOCK(curthread);
 
-               /* Map the stack and guard page together, and split guard
-                  page from allocated space: */
-               if ((stackaddr = mmap(stackaddr, stacksize+guardsize,
-                    PROT_READ | PROT_WRITE, MAP_STACK,
-                    -1, 0)) != MAP_FAILED &&
-                   (guardsize == 0 ||
-                    mprotect(stackaddr, guardsize, PROT_NONE) == 0)) {
-                       stackaddr += guardsize;
-               } else {
-                       if (stackaddr != MAP_FAILED)
+               /*
+                * Map the stack and guard page together then split the
+                * guard page from allocated space.
+                *
+                * NOTE: MAP_STACK mappings are grow-down and the
+                * initial mapping does not actually extend to the guard
+                * area, so creating the guard requires doing a fixed
+                * anonymous mmap of the guard area.
+                */
+               stackaddr = mmap(stackaddr, stacksize + guardsize,
+                                PROT_READ | PROT_WRITE, MAP_STACK, -1, 0);
+               if (stackaddr != MAP_FAILED && guardsize) {
+                       if (mmap(stackaddr, guardsize, 0,
+                                MAP_ANON | MAP_FIXED, -1, 0) == MAP_FAILED) {
                                munmap(stackaddr, stacksize + guardsize);
-                       stackaddr = NULL;
+                               stackaddr = MAP_FAILED;
+                       } else {
+                               stackaddr += guardsize;
+                       }
                }
+               if (stackaddr == MAP_FAILED)
+                       stackaddr = NULL;
                attr->stackaddr_attr = stackaddr;
        }
        if (attr->stackaddr_attr != NULL)