[PATCH 6/8] unwind: arm64: add reliable stacktrace support for arm64

[Weinan Liu <wnliu@google.com>]

To support livepatch, we need to add arch_stack_walk_reliable to
support reliable stacktrace according to
https://docs.kernel.org/livepatch/reliable-stacktrace.html#requirements

report stacktrace is not reliable if we are not able to unwind the stack
by sframe unwinder and fallback to FP based unwinder

Signed-off-by: Weinan Liu <wnliu@google.com>
---
 arch/arm64/include/asm/stacktrace/common.h |  2 +
 arch/arm64/kernel/stacktrace.c             | 47 +++++++++++++++++++++-
 2 files changed, 47 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/stacktrace/common.h b/arch/arm64/include/asm/stacktrace/common.h
index 19edae8a5b1a..26449cd402db 100644
--- a/arch/arm64/include/asm/stacktrace/common.h
+++ b/arch/arm64/include/asm/stacktrace/common.h
@@ -26,6 +26,7 @@ struct stack_info {
  * @stacks:      An array of stacks which can be unwound.
  * @nr_stacks:   The number of stacks in @stacks.
  * @cfa:         The sp value at the call site of the current function.
+ * @unreliable:  Stacktrace is unreliable.
  */
 struct unwind_state {
 	unsigned long fp;
@@ -36,6 +37,7 @@ struct unwind_state {
 	int nr_stacks;
 #ifdef CONFIG_SFRAME_UNWINDER
 	unsigned long cfa;
+	bool unreliable;
 #endif
 };
 
diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
index c035adb8fe8a..eab16dc05bb5 100644
--- a/arch/arm64/kernel/stacktrace.c
+++ b/arch/arm64/kernel/stacktrace.c
@@ -310,11 +310,16 @@ kunwind_next(struct kunwind_state *state)
 	case KUNWIND_SOURCE_TASK:
 	case KUNWIND_SOURCE_REGS_PC:
 #ifdef CONFIG_SFRAME_UNWINDER
-	err = unwind_next_frame_sframe(&state->common);
+	if (!state->common.unreliable)
+		err = unwind_next_frame_sframe(&state->common);
 
 	/* Fallback to FP based unwinder */
-	if (err)
+	if (err || state->common.unreliable) {
 		err = kunwind_next_frame_record(state);
+		/* Mark its stacktrace result as unreliable if it is unwindable via FP */
+		if (!err)
+			state->common.unreliable = true;
+	}
 #else
 	err = kunwind_next_frame_record(state);
 #endif
@@ -446,6 +451,44 @@ noinline noinstr void arch_stack_walk(stack_trace_consume_fn consume_entry,
 	kunwind_stack_walk(arch_kunwind_consume_entry, &data, task, regs);
 }
 
+#ifdef CONFIG_SFRAME_UNWINDER
+struct kunwind_reliable_consume_entry_data {
+	stack_trace_consume_fn consume_entry;
+	void *cookie;
+	bool unreliable;
+};
+
+static __always_inline bool
+arch_kunwind_reliable_consume_entry(const struct kunwind_state *state, void *cookie)
+{
+	struct kunwind_reliable_consume_entry_data *data = cookie;
+
+	if (state->common.unreliable) {
+		data->unreliable = true;
+		return false;
+	}
+	return data->consume_entry(data->cookie, state->common.pc);
+}
+
+noinline notrace int arch_stack_walk_reliable(
+				stack_trace_consume_fn consume_entry,
+				void *cookie, struct task_struct *task)
+{
+	struct kunwind_reliable_consume_entry_data data = {
+		.consume_entry = consume_entry,
+		.cookie = cookie,
+		.unreliable = false,
+	};
+
+	kunwind_stack_walk(arch_kunwind_reliable_consume_entry, &data, task, NULL);
+
+	if (data.unreliable)
+		return -EINVAL;
+
+	return 0;
+}
+#endif
+
 struct bpf_unwind_consume_entry_data {
 	bool (*consume_entry)(void *cookie, u64 ip, u64 sp, u64 fp);
 	void *cookie;
-- 
2.48.1.262.g85cc9f2d1e-goog