[RFC 1/2] arm64: Implement arch_stack_walk_reliable

[Song Liu <song@kernel.org>]

Let do_kunwind() and kunwind_stack_walk() return the state of stack walk
properly to the caller, and use them in arch_stack_walk_reliable(). This
can be used to enable livepatching for arm64.

Signed-off-by: Song Liu <song@kernel.org>
---
 arch/arm64/Kconfig             |  2 +-
 arch/arm64/kernel/stacktrace.c | 35 +++++++++++++++++++++++++++-------
 2 files changed, 29 insertions(+), 8 deletions(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 213f42d5ca27..f5af6faf9e2b 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -271,6 +271,7 @@ config ARM64
 	select HAVE_SOFTIRQ_ON_OWN_STACK
 	select USER_STACKTRACE_SUPPORT
 	select VDSO_GETRANDOM
+	select HAVE_RELIABLE_STACKTRACE
 	help
 	  ARM 64-bit (AArch64) Linux support.
 
@@ -2495,4 +2496,3 @@ endmenu # "CPU Power Management"
 source "drivers/acpi/Kconfig"
 
 source "arch/arm64/kvm/Kconfig"
-
diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
index 1d9d51d7627f..280dd6839a18 100644
--- a/arch/arm64/kernel/stacktrace.c
+++ b/arch/arm64/kernel/stacktrace.c
@@ -277,22 +277,28 @@ kunwind_next(struct kunwind_state *state)
 
 typedef bool (*kunwind_consume_fn)(const struct kunwind_state *state, void *cookie);
 
-static __always_inline void
+static __always_inline int
 do_kunwind(struct kunwind_state *state, kunwind_consume_fn consume_state,
 	   void *cookie)
 {
+	int ret;
+
 	if (kunwind_recover_return_address(state))
-		return;
+		return -EINVAL;
 
 	while (1) {
-		int ret;
 
-		if (!consume_state(state, cookie))
+		ret = consume_state(state, cookie);
+		if (!ret)
 			break;
 		ret = kunwind_next(state);
 		if (ret < 0)
 			break;
 	}
+	/* Unwind terminated successfully */
+	if (ret == -ENOENT)
+		ret = 0;
+	return ret;
 }
 
 /*
@@ -324,7 +330,7 @@ do_kunwind(struct kunwind_state *state, kunwind_consume_fn consume_state,
 			: stackinfo_get_unknown();		\
 	})
 
-static __always_inline void
+static __always_inline int
 kunwind_stack_walk(kunwind_consume_fn consume_state,
 		   void *cookie, struct task_struct *task,
 		   struct pt_regs *regs)
@@ -352,7 +358,7 @@ kunwind_stack_walk(kunwind_consume_fn consume_state,
 
 	if (regs) {
 		if (task != current)
-			return;
+			return -EINVAL;
 		kunwind_init_from_regs(&state, regs);
 	} else if (task == current) {
 		kunwind_init_from_caller(&state);
@@ -360,7 +366,7 @@ kunwind_stack_walk(kunwind_consume_fn consume_state,
 		kunwind_init_from_task(&state, task);
 	}
 
-	do_kunwind(&state, consume_state, cookie);
+	return do_kunwind(&state, consume_state, cookie);
 }
 
 struct kunwind_consume_entry_data {
@@ -387,6 +393,21 @@ noinline noinstr void arch_stack_walk(stack_trace_consume_fn consume_entry,
 	kunwind_stack_walk(arch_kunwind_consume_entry, &data, task, regs);
 }
 
+noinline noinstr int arch_stack_walk_reliable(stack_trace_consume_fn consume_entry,
+			void *cookie, struct task_struct *task)
+{
+	int ret;
+
+	struct kunwind_consume_entry_data data = {
+		.consume_entry = consume_entry,
+		.cookie = cookie,
+	};
+
+	ret = kunwind_stack_walk(arch_kunwind_consume_entry, &data, task, NULL);
+
+	return ret;
+}
+
 struct bpf_unwind_consume_entry_data {
 	bool (*consume_entry)(void *cookie, u64 ip, u64 sp, u64 fp);
 	void *cookie;
-- 
2.43.5