1 files changed, 64 insertions, 38 deletions

diff --git a/arch/powerpc/kernel/stacktrace.c b/arch/powerpc/kernel/stacktrace.c
index e2c50b55138f..1e2276963f6d 100644
--- a/arch/powerpc/kernel/stacktrace.c
+++ b/arch/powerpc/kernel/stacktrace.c
@@ -67,12 +67,17 @@ void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
 {
 	unsigned long sp;
 
+	if (!try_get_task_stack(tsk))
+		return;
+
 	if (tsk == current)
 		sp = current_stack_pointer();
 	else
 		sp = tsk->thread.ksp;
 
 	save_context_stack(trace, sp, tsk, 0);
+
+	put_task_stack(tsk);
 }
 EXPORT_SYMBOL_GPL(save_stack_trace_tsk);
 
@@ -84,25 +89,21 @@ save_stack_trace_regs(struct pt_regs *regs, struct stack_trace *trace)
 EXPORT_SYMBOL_GPL(save_stack_trace_regs);
 
 #ifdef CONFIG_HAVE_RELIABLE_STACKTRACE
-int
-save_stack_trace_tsk_reliable(struct task_struct *tsk,
-				struct stack_trace *trace)
+/*
+ * This function returns an error if it detects any unreliable features of the
+ * stack.  Otherwise it guarantees that the stack trace is reliable.
+ *
+ * If the task is not 'current', the caller *must* ensure the task is inactive.
+ */
+static int __save_stack_trace_tsk_reliable(struct task_struct *tsk,
+					   struct stack_trace *trace)
 {
 	unsigned long sp;
+	unsigned long newsp;
 	unsigned long stack_page = (unsigned long)task_stack_page(tsk);
 	unsigned long stack_end;
 	int graph_idx = 0;
-
-	/*
-	 * The last frame (unwinding first) may not yet have saved
-	 * its LR onto the stack.
-	 */
-	int firstframe = 1;
-
-	if (tsk == current)
-		sp = current_stack_pointer();
-	else
-		sp = tsk->thread.ksp;
+	bool firstframe;
 
 	stack_end = stack_page + THREAD_SIZE;
 	if (!is_idle_task(tsk)) {
@@ -129,40 +130,53 @@ save_stack_trace_tsk_reliable(struct task_struct *tsk,
 		stack_end -= STACK_FRAME_OVERHEAD;
 	}
 
+	if (tsk == current)
+		sp = current_stack_pointer();
+	else
+		sp = tsk->thread.ksp;
+
 	if (sp < stack_page + sizeof(struct thread_struct) ||
 	    sp > stack_end - STACK_FRAME_MIN_SIZE) {
-		return 1;
+		return -EINVAL;
 	}
 
-	for (;;) {
+	for (firstframe = true; sp != stack_end;
+	     firstframe = false, sp = newsp) {
 		unsigned long *stack = (unsigned long *) sp;
-		unsigned long newsp, ip;
+		unsigned long ip;
 
 		/* sanity check: ABI requires SP to be aligned 16 bytes. */
 		if (sp & 0xF)
-			return 1;
-
-		/* Mark stacktraces with exception frames as unreliable. */
-		if (sp <= stack_end - STACK_INT_FRAME_SIZE &&
-		    stack[STACK_FRAME_MARKER] == STACK_FRAME_REGS_MARKER) {
-			return 1;
-		}
+			return -EINVAL;
 
 		newsp = stack[0];
 		/* Stack grows downwards; unwinder may only go up. */
 		if (newsp <= sp)
-			return 1;
+			return -EINVAL;
 
 		if (newsp != stack_end &&
 		    newsp > stack_end - STACK_FRAME_MIN_SIZE) {
-			return 1; /* invalid backlink, too far up. */
+			return -EINVAL; /* invalid backlink, too far up. */
+		}
+
+		/*
+		 * We can only trust the bottom frame's backlink, the
+		 * rest of the frame may be uninitialized, continue to
+		 * the next.
+		 */
+		if (firstframe)
+			continue;
+
+		/* Mark stacktraces with exception frames as unreliable. */
+		if (sp <= stack_end - STACK_INT_FRAME_SIZE &&
+		    stack[STACK_FRAME_MARKER] == STACK_FRAME_REGS_MARKER) {
+			return -EINVAL;
 		}
 
 		/* Examine the saved LR: it must point into kernel code. */
 		ip = stack[STACK_FRAME_LR_SAVE];
-		if (!firstframe && !__kernel_text_address(ip))
-			return 1;
-		firstframe = 0;
+		if (!__kernel_text_address(ip))
+			return -EINVAL;
 
 		/*
 		 * FIXME: IMHO these tests do not belong in
@@ -175,25 +189,37 @@ save_stack_trace_tsk_reliable(struct task_struct *tsk,
 		 * as unreliable.
 		 */
 		if (ip == (unsigned long)kretprobe_trampoline)
-			return 1;
+			return -EINVAL;
 #endif
 
+		if (trace->nr_entries >= trace->max_entries)
+			return -E2BIG;
 		if (!trace->skip)
 			trace->entries[trace->nr_entries++] = ip;
 		else
 			trace->skip--;
+	}
+	return 0;
+}
 
-		if (newsp == stack_end)
-			break;
+int save_stack_trace_tsk_reliable(struct task_struct *tsk,
+				  struct stack_trace *trace)
+{
+	int ret;
 
-		if (trace->nr_entries >= trace->max_entries)
-			return -E2BIG;
+	/*
+	 * If the task doesn't have a stack (e.g., a zombie), the stack is
+	 * "reliably" empty.
+	 */
+	if (!try_get_task_stack(tsk))
+		return 0;
 
-		sp = newsp;
-	}
-	return 0;
+	ret = __save_stack_trace_tsk_reliable(tsk, trace);
+
+	put_task_stack(tsk);
+
+	return ret;
 }
-EXPORT_SYMBOL_GPL(save_stack_trace_tsk_reliable);
 #endif /* CONFIG_HAVE_RELIABLE_STACKTRACE */
 
 #if defined(CONFIG_PPC_BOOK3S_64) && defined(CONFIG_NMI_IPI)