linux-kernel - Re: [PATCH] tracing: Fix align of static buffer

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Date:   Thu, 26 Nov 2020 18:31:35 +0900
From:   Namhyung Kim <namhyung@...nel.org>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Minchan Kim <minchan@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "stable # 4 . 5" <stable@...r.kernel.org>
Subject: Re: [PATCH] tracing: Fix align of static buffer

Hi Greg,

On Thu, Nov 26, 2020 at 2:52 PM Greg KH <gregkh@...uxfoundation.org> wrote:
>
> On Wed, Nov 25, 2020 at 02:56:54PM -0800, Minchan Kim wrote:
> > With 5.9 kernel on ARM64, I found ftrace_dump output was broken but
> > it had no problem with normal output "cat /sys/kernel/debug/tracing/trace".
> >
> > With investigation, it seems coping the data into temporal buffer seems to
> > break the align binary printf expects if the static buffer is not aligned
> > with 4-byte. IIUC, get_arg in bstr_printf expects that args has already
> > right align to be decoded and seq_buf_bprintf says ``the arguments are saved
> > in a 32bit word array that is defined by the format string constraints``.
> > So if we don't keep the align under copy to temporal buffer, the output
> > will be broken by shifting some bytes.
> >
> > This patch fixes it.
>
> Does this resolve the issue reported at:
>         https://lore.kernel.org/r/20201124223917.795844-1-elavila@google.com
> ?

No, it's a different issue.

Thanks,
Namhyung