linux-kernel - Re: [RFC/PATCH 2/2] pstore: Convert console write to use ->write

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Date:   Tue, 15 Nov 2016 15:21:25 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Anton Vorontsov <anton@...msg.org>,
        Colin Cross <ccross@...roid.com>,
        Tony Luck <tony.luck@...el.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Stefan Hajnoczi <stefanha@...hat.com>
Subject: Re: [RFC/PATCH 2/2] pstore: Convert console write to use ->write_buf

On Tue, Oct 18, 2016 at 6:23 PM, Namhyung Kim <namhyung@...nel.org> wrote:
> Maybe I'm missing something, but I don't know why it needs to copy the
> input buffer to psinfo->buf and then write.  Instead we can write the
> input buffer directly.  The only implementation that supports console
> message (i.e. ramoops) already does it for ftrace messages.
>
> For the upcoming virtio backend driver, it needs to protect psinfo->buf
> overwritten from console messages.  If it could use ->write_buf method
> instead of ->write, the problem will be solved easily.

Agreed, this looks like needless bounce-buffering. Thanks!

-Kees

>
> Cc: Stefan Hajnoczi <stefanha@...hat.com>
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> ---
>  fs/pstore/platform.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c
> index 14984d902a99..960d66251bab 100644
> --- a/fs/pstore/platform.c
> +++ b/fs/pstore/platform.c
> @@ -584,8 +584,8 @@ static void pstore_console_write(struct console *con, const char *s, unsigned c)
>                 } else {
>                         spin_lock_irqsave(&psinfo->buf_lock, flags);
>                 }
> -               memcpy(psinfo->buf, s, c);
> -               psinfo->write(PSTORE_TYPE_CONSOLE, 0, &id, 0, 0, 0, c, psinfo);
> +               psinfo->write_buf(PSTORE_TYPE_CONSOLE, 0, &id, 0,
> +                                 s, 0, c, psinfo);
>                 spin_unlock_irqrestore(&psinfo->buf_lock, flags);
>                 s += c;
>                 c = e - s;
> --
> 2.9.3
>



-- 
Kees Cook
Nexus Security