linux-kernel - Re: [PATCH v4 04/18] arm64: stacktrace: Handle frame pointer from different address spaces

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Message-ID: <CA+EHjTzv9VFnp+6kCw0pMuUxqXtmthujg7ga=Fkexz9jEq29LA@mail.gmail.com>
Date:   Fri, 15 Jul 2022 14:56:44 +0100
From:   Fuad Tabba <tabba@...gle.com>
To:     Kalesh Singh <kaleshsingh@...gle.com>
Cc:     maz@...nel.org, mark.rutland@....com, broonie@...nel.org,
        madvenka@...ux.microsoft.com, will@...nel.org, qperret@...gle.com,
        james.morse@....com, alexandru.elisei@....com,
        suzuki.poulose@....com, catalin.marinas@....com,
        andreyknvl@...il.com, russell.king@...cle.com,
        vincenzo.frascino@....com, mhiramat@...nel.org, ast@...nel.org,
        drjones@...hat.com, wangkefeng.wang@...wei.com, elver@...gle.com,
        keirf@...gle.com, yuzenghui@...wei.com, ardb@...nel.org,
        oupton@...gle.com, linux-arm-kernel@...ts.infradead.org,
        kvmarm@...ts.cs.columbia.edu, linux-kernel@...r.kernel.org,
        android-mm@...gle.com, kernel-team@...roid.com
Subject: Re: [PATCH v4 04/18] arm64: stacktrace: Handle frame pointer from
 different address spaces

Hi Kalesh,

On Fri, Jul 15, 2022 at 7:11 AM 'Kalesh Singh' via kernel-team
<kernel-team@...roid.com> wrote:
>
> The unwinder code is made reusable so that it can be used to
> unwind various types of stacks. One usecase is unwinding the
> nVHE hyp stack from the host (EL1) in non-protected mode. This
> means that the unwinder must be able to tracnslate HYP stack

s/tracnslate/translate

> addresses to kernel addresses.
>
> Add a callback (stack_trace_translate_fp_fn) to allow specifying
> the translation function.
>
> Signed-off-by: Kalesh Singh <kaleshsingh@...gle.com>
> ---
>  arch/arm64/include/asm/stacktrace/common.h | 26 ++++++++++++++++++++--
>  arch/arm64/kernel/stacktrace.c             |  2 +-
>  2 files changed, 25 insertions(+), 3 deletions(-)
>
> diff --git a/arch/arm64/include/asm/stacktrace/common.h b/arch/arm64/include/asm/stacktrace/common.h
> index 0c5cbfdb56b5..5f5d74a286f3 100644
> --- a/arch/arm64/include/asm/stacktrace/common.h
> +++ b/arch/arm64/include/asm/stacktrace/common.h
> @@ -123,9 +123,22 @@ static inline void unwind_init_common(struct unwind_state *state,
>         state->prev_fp = 0;
>         state->prev_type = STACK_TYPE_UNKNOWN;
>  }
> +/**
> + * stack_trace_translate_fp_fn() - Translates a non-kernel frame pointer to
> + * a kernel address.
> + *
> + * @fp:   the frame pointer to be updated to it's kernel address.
> + * @type: the stack type associated with frame pointer @fp
> + *
> + * Returns true and success and @fp is updated to the corresponding
> + * kernel virtual address; otherwise returns false.
> + */

Please add a newline before the new block.

Also, something which you have done in comment blocks in this patch as
well as future patches (so I won't mention them again) is use the
opening comment mark /** , which is meant for kernel-doc comments
(https://www.kernel.org/doc/html/latest/doc-guide/kernel-doc.html).
However, this block, and many if not most of the others don't seem to
be conformant (scripts/kernel-doc -v -none
arch/arm64/include/asm/stacktrace/common.h).

I think the easiest thing to do is to format them as a normal block: /*.


> +typedef bool (*stack_trace_translate_fp_fn)(unsigned long *fp,
> +                                           enum stack_type type);
>
>  static inline int unwind_next_common(struct unwind_state *state,
> -                                    struct stack_info *info)
> +                                    struct stack_info *info,
> +                                    stack_trace_translate_fp_fn translate_fp)
>  {
>         struct task_struct *tsk = state->task;
>         unsigned long fp = state->fp;
> @@ -159,13 +172,22 @@ static inline int unwind_next_common(struct unwind_state *state,
>                 __set_bit(state->prev_type, state->stacks_done);
>         }
>
> +       /* Record fp as prev_fp before attempting to get the next fp */
> +       state->prev_fp = fp;
> +
> +       /*
> +        * If fp is not from the current address space perform the necessary
> +        * translation before dereferencing it to get the next fp.
> +        */
> +       if (translate_fp && !translate_fp(&fp, info->type))
> +               return -EINVAL;
> +

A call to unwind_next_common could fail having updated state->prev_fp
as well as state->stacks_done. I think that it might be better to
rework it so that there aren't any side effects should a call fail.

Thanks,
/fuad





>         /*
>          * 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;
> diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
> index 834851939364..eef3cf6bf2d7 100644
> --- a/arch/arm64/kernel/stacktrace.c
> +++ b/arch/arm64/kernel/stacktrace.c
> @@ -87,7 +87,7 @@ static int notrace unwind_next(struct unwind_state *state)
>         if (fp == (unsigned long)task_pt_regs(tsk)->stackframe)
>                 return -ENOENT;
>
> -       err = unwind_next_common(state, &info);
> +       err = unwind_next_common(state, &info, NULL);
>         if (err)
>                 return err;
>
> --
> 2.37.0.170.g444d1eabd0-goog
>
> --
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>