[RFC PATCH v15 6/6] arm64: Introduce arch_stack_walk_reliable()

[madvenka@linux.microsoft.com]

From: "Madhavan T. Venkataraman" <madvenka@linux.microsoft.com>

Introduce arch_stack_walk_reliable() for ARM64. This works like
arch_stack_walk() except that it returns -EINVAL if the stack trace is not
reliable.

Until all the reliability checks are in place, arch_stack_walk_reliable()
may not be used by livepatch. But it may be used by debug and test code.

Signed-off-by: Madhavan T. Venkataraman <madvenka@linux.microsoft.com>
Reviewed-by: Mark Brown <broonie@kernel.org>
---
 arch/arm64/kernel/stacktrace.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
index eda8581f7dbe..8016ba0e2c96 100644
--- a/arch/arm64/kernel/stacktrace.c
+++ b/arch/arm64/kernel/stacktrace.c
@@ -383,3 +383,26 @@ noinline notrace void arch_stack_walk(stack_trace_consume_fn consume_entry,
 
 	unwind(&state, consume_entry, cookie);
 }
+
+/*
+ * arch_stack_walk_reliable() may not be used for livepatch until all of
+ * the reliability checks are in place in unwind_consume(). However,
+ * debug and test code can choose to use it even if all the checks are not
+ * in place.
+ */
+noinline int notrace arch_stack_walk_reliable(
+					stack_trace_consume_fn consume_entry,
+					void *cookie,
+					struct task_struct *task)
+{
+	struct unwind_state state;
+	bool reliable;
+
+	if (task == current)
+		unwind_init_from_caller(&state);
+	else
+		unwind_init_from_task(&state, task);
+
+	reliable = unwind(&state, consume_entry, cookie);
+	return reliable ? 0 : -EINVAL;
+}
-- 
2.25.1