arm64: stacktrace: recover return address for first entry

The function which calls the top-level backtracing function may have
been instrumented with ftrace and/or kprobes, and hence the first return
address may have been rewritten.

Factor out the existing fgraph / kretprobes address recovery, and use
this for the first address. As the comment for the fgraph case isn't all
that helpful, I've also dropped that.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Kalesh Singh <kaleshsingh@google.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Madhavan T. Venkataraman <madvenka@linux.microsoft.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20230411162943.203199-2-mark.rutland@arm.com
Signed-off-by: Will Deacon <will@kernel.org>

diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
index 8315430..dd03feb 100644 (file)
--- a/arch/arm64/kernel/stacktrace.c
+++ b/arch/arm64/kernel/stacktrace.c
@@ -69,6 +69,32 @@ static __always_inline void unwind_init_from_task(struct unwind_state *state,
        state->pc = thread_saved_pc(task);
 }
 
+static __always_inline int
+unwind_recover_return_address(struct unwind_state *state)
+{
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+       if (state->task->ret_stack &&
+           (state->pc == (unsigned long)return_to_handler)) {
+               unsigned long orig_pc;
+               orig_pc = ftrace_graph_ret_addr(state->task, NULL, state->pc,
+                                               (void *)state->fp);
+               if (WARN_ON_ONCE(state->pc == orig_pc))
+                       return -EINVAL;
+               state->pc = orig_pc;
+       }
+#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
+
+#ifdef CONFIG_KRETPROBES
+       if (is_kretprobe_trampoline(state->pc)) {
+               state->pc = kretprobe_find_ret_addr(state->task,
+                                                   (void *)state->fp,
+                                                   &state->kr_cur);
+       }
+#endif /* CONFIG_KRETPROBES */
+
+       return 0;
+}
+
 /*
  * Unwind from one frame record (A) to the next frame record (B).
  *
@@ -92,35 +118,16 @@ static int notrace unwind_next(struct unwind_state *state)
 
        state->pc = ptrauth_strip_insn_pac(state->pc);
 
-#ifdef CONFIG_FUNCTION_GRAPH_TRACER
-       if (tsk->ret_stack &&
-               (state->pc == (unsigned long)return_to_handler)) {
-               unsigned long orig_pc;
-               /*
-                * This is a case where function graph tracer has
-                * modified a return address (LR) in a stack frame
-                * to hook a function return.
-                * So replace it to an original value.
-                */
-               orig_pc = ftrace_graph_ret_addr(tsk, NULL, state->pc,
-                                               (void *)state->fp);
-               if (WARN_ON_ONCE(state->pc == orig_pc))
-                       return -EINVAL;
-               state->pc = orig_pc;
-       }
-#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
-#ifdef CONFIG_KRETPROBES
-       if (is_kretprobe_trampoline(state->pc))
-               state->pc = kretprobe_find_ret_addr(tsk, (void *)state->fp, &state->kr_cur);
-#endif
-
-       return 0;
+       return unwind_recover_return_address(state);
 }
 NOKPROBE_SYMBOL(unwind_next);
 
 static void notrace unwind(struct unwind_state *state,
                           stack_trace_consume_fn consume_entry, void *cookie)
 {
+       if (unwind_recover_return_address(state))
+               return;
+
        while (1) {
                int ret;