[committed][PATCH v3][BZ #22637] Fix stack guard size accounting

[committed][PATCH v3][BZ #22637] Fix stack guard size accounting

[Szabolcs Nagy]

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v3:
- add comments about stackblock_size to nptl/descr.h
- add comments to nptl/pthread_getattr_np.c
v2:
- use separate bug number from the tls accounting issue.
- check for arithmetic overflow in size+guardsize.

Previously if user requested S stack and G guard when creating a
thread, the total mapping was S and the actual available stack was
S - G - static_tls, which is not what the user requested.

This patch fixes the guard size accounting by pretending the user
requested S+G stack.  This way all later logic works out except
when reporting the user requested stack size (pthread_getattr_np)
or when computing the minimal stack size (__pthread_get_minstack).

Normally this will increase thread stack allocations by one page.
TLS accounting is not affected, that will require a separate fix.

	[BZ #22637]
	* nptl/descr.h (stackblock, stackblock_size): Update comments.
	* nptl/allocatestack.c (allocate_stack): Add guardsize to stacksize.
	* nptl/nptl-init.c (__pthread_get_minstack): Remove guardsize from
	stacksize.
	* nptl/pthread_getattr_np.c (pthread_getattr_np): Likewise.

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diff --git a/nptl/allocatestack.c b/nptl/allocatestack.c
index 05b8ed331b..b374f4794d 100644
--- a/nptl/allocatestack.c
+++ b/nptl/allocatestack.c
@@ -532,6 +532,10 @@ allocate_stack (const struct pthread_attr *attr, struct pthread **pdp,
       /* Make sure the size of the stack is enough for the guard and
 	 eventually the thread descriptor.  */
       guardsize = (attr->guardsize + pagesize_m1) & ~pagesize_m1;
+      if (guardsize < attr->guardsize || size + guardsize < guardsize)
+	/* Arithmetic overflow.  */
+	return EINVAL;
+      size += guardsize;
       if (__builtin_expect (size < ((guardsize + __static_tls_size
 				     + MINIMAL_REST_STACK + pagesize_m1)
 				    & ~pagesize_m1),
diff --git a/nptl/descr.h b/nptl/descr.h
index da9c567a6f..1cc6b09d1e 100644
--- a/nptl/descr.h
+++ b/nptl/descr.h
@@ -383,9 +383,9 @@ struct pthread
   /* Machine-specific unwind info.  */
   struct _Unwind_Exception exc;
 
-  /* If nonzero pointer to area allocated for the stack and its
-     size.  */
+  /* If nonzero, pointer to the area allocated for the stack and guard. */
   void *stackblock;
+  /* Size of the stackblock area including the guard.  */
   size_t stackblock_size;
   /* Size of the included guard area.  */
   size_t guardsize;
diff --git a/nptl/nptl-init.c b/nptl/nptl-init.c
index c237a3675a..5a4b52419f 100644
--- a/nptl/nptl-init.c
+++ b/nptl/nptl-init.c
@@ -472,8 +472,5 @@ strong_alias (__pthread_initialize_minimal_internal,
 size_t
 __pthread_get_minstack (const pthread_attr_t *attr)
 {
-  struct pthread_attr *iattr = (struct pthread_attr *) attr;
-
-  return (GLRO(dl_pagesize) + __static_tls_size + PTHREAD_STACK_MIN
-	  + iattr->guardsize);
+  return GLRO(dl_pagesize) + __static_tls_size + PTHREAD_STACK_MIN;
 }
diff --git a/nptl/pthread_getattr_np.c b/nptl/pthread_getattr_np.c
index 961d711fd2..ae12592294 100644
--- a/nptl/pthread_getattr_np.c
+++ b/nptl/pthread_getattr_np.c
@@ -57,9 +57,12 @@ pthread_getattr_np (pthread_t thread_id, pthread_attr_t *attr)
   /* The sizes are subject to alignment.  */
   if (__glibc_likely (thread->stackblock != NULL))
     {
-      iattr->stacksize = thread->stackblock_size;
+      /* The stack size reported to the user should not include the
+	 guard size.  */
+      iattr->stacksize = thread->stackblock_size - thread->guardsize;
 #if _STACK_GROWS_DOWN
-      iattr->stackaddr = (char *) thread->stackblock + iattr->stacksize;
+      iattr->stackaddr = (char *) thread->stackblock
+			 + thread->stackblock_size;
 #else
       iattr->stackaddr = (char *) thread->stackblock;
 #endif