1 files changed, 18 insertions, 4 deletions

diff --git a/arch/x86/kernel/unwind_guess.c b/arch/x86/kernel/unwind_guess.c
index 9298993..22881dd 100644
--- a/arch/x86/kernel/unwind_guess.c
+++ b/arch/x86/kernel/unwind_guess.c
@@ -7,11 +7,15 @@
 
 unsigned long unwind_get_return_address(struct unwind_state *state)
 {
+	unsigned long addr;
+
 	if (unwind_done(state))
 		return 0;
 
+	addr = READ_ONCE_NOCHECK(*state->sp);
+
 	return ftrace_graph_ret_addr(state->task, &state->graph_idx,
-				     *state->sp, state->sp);
+				     addr, state->sp);
 }
 EXPORT_SYMBOL_GPL(unwind_get_return_address);
 
@@ -23,9 +27,12 @@ bool unwind_next_frame(struct unwind_state *state)
 		return false;
 
 	do {
-		for (state->sp++; state->sp < info->end; state->sp++)
-			if (__kernel_text_address(*state->sp))
+		for (state->sp++; state->sp < info->end; state->sp++) {
+			unsigned long addr = READ_ONCE_NOCHECK(*state->sp);
+
+			if (__kernel_text_address(addr))
 				return true;
+		}
 
 		state->sp = info->next_sp;
 
@@ -47,7 +54,14 @@ void __unwind_start(struct unwind_state *state, struct task_struct *task,
 	get_stack_info(first_frame, state->task, &state->stack_info,
 		       &state->stack_mask);
 
-	if (!__kernel_text_address(*first_frame))
+	/*
+	 * The caller can provide the address of the first frame directly
+	 * (first_frame) or indirectly (regs->sp) to indicate which stack frame
+	 * to start unwinding at.  Skip ahead until we reach it.
+	 */
+	if (!unwind_done(state) &&
+	    (!on_stack(&state->stack_info, first_frame, sizeof(long)) ||
+	    !__kernel_text_address(*first_frame)))
 		unwind_next_frame(state);
 }
 EXPORT_SYMBOL_GPL(__unwind_start);