Re: [Xen-devel] [PATCH v2 1/4] xen/console: Don't treat NUL character as the end of the buffer

[Julien Grall <julien.grall@xxxxxxx>]

Hi Stefano,

On 10/2/19 2:25 AM, Stefano Stabellini wrote:
> On Mon, 5 Aug 2019, Julien Grall wrote:
> > After upgrading Debian to Buster, I have began to notice console
> > mangling when using zsh in Dom0. This is happenning because output sent by
> > zsh to the console may contain NULs in the middle of the buffer.Hi,
> >
> > The actual implementation of CONSOLEIO_write considers that a buffer
> > always terminate with a NUL and therefore will ignore anything after it.
> >
> > In general, NULs are perfectly legitimate in terminal streams. For
> > instance, this could be used for padding slow terminals. See terminfo(5)
> > section `Delays and Padding`, or search for the pcre '\bpad'.
> >
> > Other use cases includes using the console for dumping non-human
> > readable information (e.g debugger, file if no network...). With the
> > current behavior, the resulting stream will end up to be corrupted.
> >
> > The documentation for CONSOLEIO_write is pretty limited (to not say
> > inexistent). From the declaration, the hypercall takes a buffer and size.
> > So this could lead to think the NUL character is allowed in the middle of
> > the buffer.
> >
> > This patch updates the console API to pass the size along the buffer
> > down so we can remove the reliance on buffer terminating by a NUL
> > character.
> >
> > Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
> >
> > ---
> >
> > This patch was originally sent standalone [1]. But the series grows to
> > include another bug found in the console code and documentation.
> >
> > Cnhanges in v2:
> >      - Switch from unsigned int to size_t. So truncation is avoided. We
> >      can decide whether we want explicit truncation later on.
> >      - Remove unecessary leading NUL added in dump_console_ring_key
> >      - Remove unecessary decoration in sercon_puts
> >      - Fix loop in lfb_scroll_puts
> >      - use while() rather than do {} while()
> >
> > Change since the standalone version:
> >      - Fix early printk on Arm
> >      - Fix gdbstub
> >      - Remove unecessary leading NUL character added by Xen
> >      - Handle DomU console
> >      - Rework the commit message
> >
> > Below a small C program to repro the bug on Xen:
> >
> > int main(void)
> > {
> >      write(1,
> >            
> > "\r\33[0m\0\0\0\0\0\0\0\0\33[27m\33[24m\33[j\33[32mjulien\33[31m@\33[00m\33[36mjuno2-julieng:~\33[37m>",
> >            75);
> >      write(1,
> >            "\33[K\33[32C\33[01;33m--juno2-julieng-13:44--\33[00m\33[37m\33[55D",
> >            54);
> >      write(1, "\33[?2004h", 8);
> >
> >      return 0;
> > }
> >
> > Without this patch, the only --juno2-julieng-13:44-- will be printed in
> > yellow.
> >
> > This patch was tested on Arm using serial console. I am not entirely
> > sure whether the video and PV console is correct. I would appreciate help
> > for testing here.
> >
> > [1] https://lists.xenproject.org/archives/html/xen-devel/2019-02/msg01932.html
> Acked-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
Thank you for the acked-by. Although, this was already merged 2 months ago.

Cheers,


--
Julien Grall

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