[PATCH 1/3] arm64: stacktrace: recover return address for first entry

[Kalesh Singh]

On Fri, Mar 24, 2023 at 6:50 AM Mark Rutland <mark.rutland at arm.com> wrote:
>
> 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 at arm.com>
> Cc: Catalin Marinas <catalin.marinas at arm.com>
> Cc: Kalesh Singh <kaleshsingh at google.com>
> Cc: Madhavan T. Venkataraman <madvenka at linux.microsoft.com>
> Cc: Mark Brown <broonie at kernel.org>
> Cc: Will Deacon <will at kernel.org>

Reviewed-by: Kalesh Singh <kaleshsingh at google.com>

Thanks,
Kalesh

> ---
>  arch/arm64/kernel/stacktrace.c | 52 +++++++++++++++++++---------------
>  1 file changed, 29 insertions(+), 23 deletions(-)
>
> diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
> index 83154303e682c..219ce0668a3dd 100644
> --- a/arch/arm64/kernel/stacktrace.c
> +++ b/arch/arm64/kernel/stacktrace.c
> @@ -69,6 +69,31 @@ 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)
> +{
> +       struct task_struct *tsk = state->task;
> +
> +#ifdef CONFIG_FUNCTION_GRAPH_TRACER
> +       if (tsk->ret_stack &&
> +           (state->pc == (unsigned long)return_to_handler)) {
> +               unsigned long orig_pc;
> +               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 /* CONFIG_KRETPROBES */
> +
> +       return 0;
> +}
> +
>  /*
>   * Unwind from one frame record (A) to the next frame record (B).
>   *
> @@ -92,35 +117,16 @@ 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;
>
> --
> 2.30.2
>