Re: [PATCH v4 03/18] arm64: stacktrace: Factor out unwind_next_common()

[Fuad Tabba <tabba@google.com>]

Hi Kalesh,

On Fri, Jul 15, 2022 at 7:11 AM Kalesh Singh <kaleshsingh@google.com> wrote:
>
> Move common unwind_next logic to stacktrace/common.h. This allows
> reusing the code in the implementation the nVHE hypervisor stack
> unwinder, later in this series.
>
> Signed-off-by: Kalesh Singh <kaleshsingh@google.com>

Reviewed-by: Fuad Tabba <tabba@google.com>

Thanks,
/fuad


> ---
>  arch/arm64/include/asm/stacktrace/common.h | 50 ++++++++++++++++++++++
>  arch/arm64/kernel/stacktrace.c             | 41 ++----------------
>  2 files changed, 54 insertions(+), 37 deletions(-)
>
> diff --git a/arch/arm64/include/asm/stacktrace/common.h b/arch/arm64/include/asm/stacktrace/common.h
> index f58b786460d3..0c5cbfdb56b5 100644
> --- a/arch/arm64/include/asm/stacktrace/common.h
> +++ b/arch/arm64/include/asm/stacktrace/common.h
> @@ -65,6 +65,10 @@ struct unwind_state {
>  static inline bool on_overflow_stack(unsigned long sp, unsigned long size,
>                                      struct stack_info *info);
>
> +static inline bool on_accessible_stack(const struct task_struct *tsk,
> +                                      unsigned long sp, unsigned long size,
> +                                      struct stack_info *info);
> +
>  static inline bool on_stack(unsigned long sp, unsigned long size,
>                             unsigned long low, unsigned long high,
>                             enum stack_type type, struct stack_info *info)
> @@ -120,4 +124,50 @@ static inline void unwind_init_common(struct unwind_state *state,
>         state->prev_type = STACK_TYPE_UNKNOWN;
>  }
>
> +static inline int unwind_next_common(struct unwind_state *state,
> +                                    struct stack_info *info)
> +{
> +       struct task_struct *tsk = state->task;
> +       unsigned long fp = state->fp;
> +
> +       if (fp & 0x7)
> +               return -EINVAL;
> +
> +       if (!on_accessible_stack(tsk, fp, 16, info))
> +               return -EINVAL;
> +
> +       if (test_bit(info->type, state->stacks_done))
> +               return -EINVAL;
> +
> +       /*
> +        * As stacks grow downward, any valid record on the same stack must be
> +        * at a strictly higher address than the prior record.
> +        *
> +        * Stacks can nest in several valid orders, e.g.
> +        *
> +        * TASK -> IRQ -> OVERFLOW -> SDEI_NORMAL
> +        * TASK -> SDEI_NORMAL -> SDEI_CRITICAL -> OVERFLOW
> +        *
> +        * ... but the nesting itself is strict. Once we transition from one
> +        * stack to another, it's never valid to unwind back to that first
> +        * stack.
> +        */
> +       if (info->type == state->prev_type) {
> +               if (fp <= state->prev_fp)
> +                       return -EINVAL;
> +       } else {
> +               __set_bit(state->prev_type, state->stacks_done);
> +       }
> +
> +       /*
> +        * Record this frame record's values and location. The prev_fp and
> +        * prev_type are only meaningful to the next unwind_next() invocation.
> +        */
> +       state->fp = READ_ONCE(*(unsigned long *)(fp));
> +       state->pc = READ_ONCE(*(unsigned long *)(fp + 8));
> +       state->prev_fp = fp;
> +       state->prev_type = info->type;
> +
> +       return 0;
> +}
>  #endif /* __ASM_STACKTRACE_COMMON_H */
> diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
> index 94a5dd2ab8fd..834851939364 100644
> --- a/arch/arm64/kernel/stacktrace.c
> +++ b/arch/arm64/kernel/stacktrace.c
> @@ -81,48 +81,15 @@ static int notrace unwind_next(struct unwind_state *state)
>         struct task_struct *tsk = state->task;
>         unsigned long fp = state->fp;
>         struct stack_info info;
> +       int err;
>
>         /* Final frame; nothing to unwind */
>         if (fp == (unsigned long)task_pt_regs(tsk)->stackframe)
>                 return -ENOENT;
>
> -       if (fp & 0x7)
> -               return -EINVAL;
> -
> -       if (!on_accessible_stack(tsk, fp, 16, &info))
> -               return -EINVAL;
> -
> -       if (test_bit(info.type, state->stacks_done))
> -               return -EINVAL;
> -
> -       /*
> -        * As stacks grow downward, any valid record on the same stack must be
> -        * at a strictly higher address than the prior record.
> -        *
> -        * Stacks can nest in several valid orders, e.g.
> -        *
> -        * TASK -> IRQ -> OVERFLOW -> SDEI_NORMAL
> -        * TASK -> SDEI_NORMAL -> SDEI_CRITICAL -> OVERFLOW
> -        *
> -        * ... but the nesting itself is strict. Once we transition from one
> -        * stack to another, it's never valid to unwind back to that first
> -        * stack.
> -        */
> -       if (info.type == state->prev_type) {
> -               if (fp <= state->prev_fp)
> -                       return -EINVAL;
> -       } else {
> -               __set_bit(state->prev_type, state->stacks_done);
> -       }
> -
> -       /*
> -        * Record this frame record's values and location. The prev_fp and
> -        * prev_type are only meaningful to the next unwind_next() invocation.
> -        */
> -       state->fp = READ_ONCE(*(unsigned long *)(fp));
> -       state->pc = READ_ONCE(*(unsigned long *)(fp + 8));
> -       state->prev_fp = fp;
> -       state->prev_type = info.type;
> +       err = unwind_next_common(state, &info);
> +       if (err)
> +               return err;
>
>         state->pc = ptrauth_strip_insn_pac(state->pc);
>
> --
> 2.37.0.170.g444d1eabd0-goog
>