1 files changed, 28 insertions, 2 deletions

diff --git a/arch/x86/kernel/unwind_frame.c b/arch/x86/kernel/unwind_frame.c
index 4443e499f279..23d15565d02a 100644
--- a/arch/x86/kernel/unwind_frame.c
+++ b/arch/x86/kernel/unwind_frame.c
@@ -6,6 +6,21 @@
 
 #define FRAME_HEADER_SIZE (sizeof(long) * 2)
 
+/*
+ * This disables KASAN checking when reading a value from another task's stack,
+ * since the other task could be running on another CPU and could have poisoned
+ * the stack in the meantime.
+ */
+#define READ_ONCE_TASK_STACK(task, x)			\
+({							\
+	unsigned long val;				\
+	if (task == current)				\
+		val = READ_ONCE(x);			\
+	else						\
+		val = READ_ONCE_NOCHECK(x);		\
+	val;						\
+})
+
 static void unwind_dump(struct unwind_state *state, unsigned long *sp)
 {
 	static bool dumped_before = false;
@@ -48,7 +63,8 @@ unsigned long unwind_get_return_address(struct unwind_state *state)
 	if (state->regs && user_mode(state->regs))
 		return 0;
 
-	addr = ftrace_graph_ret_addr(state->task, &state->graph_idx, *addr_p,
+	addr = READ_ONCE_TASK_STACK(state->task, *addr_p);
+	addr = ftrace_graph_ret_addr(state->task, &state->graph_idx, addr,
 				     addr_p);
 
 	return __kernel_text_address(addr) ? addr : 0;
@@ -162,7 +178,7 @@ bool unwind_next_frame(struct unwind_state *state)
 	if (state->regs)
 		next_bp = (unsigned long *)state->regs->bp;
 	else
-		next_bp = (unsigned long *)*state->bp;
+		next_bp = (unsigned long *)READ_ONCE_TASK_STACK(state->task,*state->bp);
 
 	/* is the next frame pointer an encoded pointer to pt_regs? */
 	regs = decode_frame_pointer(next_bp);
@@ -207,6 +223,16 @@ bool unwind_next_frame(struct unwind_state *state)
 	return true;
 
 bad_address:
+	/*
+	 * When unwinding a non-current task, the task might actually be
+	 * running on another CPU, in which case it could be modifying its
+	 * stack while we're reading it.  This is generally not a problem and
+	 * can be ignored as long as the caller understands that unwinding
+	 * another task will not always succeed.
+	 */
+	if (state->task != current)
+		goto the_end;
+
 	if (state->regs) {
 		printk_deferred_once(KERN_WARNING
 			"WARNING: kernel stack regs at %p in %s:%d has bad 'bp' value %p\n",