linux-kernel - Re: [PATCH v3 1/3] vt: preserve unicode values corresponding to screen characters

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Message-ID: <CAGXu5j+KLvJ-n_QRrfq15E8iO_rqfpp+K7PDAZHZMHcemy9y7g@mail.gmail.com>
Date:   Tue, 10 Jul 2018 17:52:01 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Nicolas Pitre <nicolas.pitre@...aro.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Dave Mielke <Dave@...lke.cc>,
        Samuel Thibault <samuel.thibault@...-lyon.org>,
        Adam Borowski <kilobyte@...band.pl>,
        Alan Cox <gnomes@...rguk.ukuu.org.uk>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-console@...r.kernel.org
Subject: Re: [PATCH v3 1/3] vt: preserve unicode values corresponding to
 screen characters

On Tue, Jun 26, 2018 at 8:56 PM, Nicolas Pitre <nicolas.pitre@...aro.org> wrote:
> The vt code translates UTF-8 strings into glyph index values and stores
> those glyph values directly in the screen buffer. Because there can only
> be at most 512 glyphs, it is impossible to represent most unicode
> characters, in which case a default glyph (often '?') is displayed
> instead. The original unicode value is then lost.
>
> This patch implements the basic screen buffer handling to preserve unicode
> values alongside corresponding display glyphs.  It is not activated by
> default, meaning that people not relying on that functionality won't get
> the implied overhead.
>
> Signed-off-by: Nicolas Pitre <nico@...aro.org>
> Tested-by: Dave Mielke <Dave@...lke.cc>
> Acked-by: Adam Borowski <kilobyte@...band.pl>
> ---
>  drivers/tty/vt/vt.c            | 220 +++++++++++++++++++++++++++++++--
>  include/linux/console_struct.h |   2 +
>  2 files changed, 211 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
> index 1eb1a376a0..7b636638b3 100644
> --- a/drivers/tty/vt/vt.c
> +++ b/drivers/tty/vt/vt.c
> [...]
> +static void vc_uniscr_scroll(struct vc_data *vc, unsigned int t, unsigned int b,
> +                            enum con_scroll dir, unsigned int nr)
> +{
> +       struct uni_screen *uniscr = get_vc_uniscr(vc);
> +
> +       if (uniscr) {
> +               unsigned int s, d, rescue, clear;
> +               char32_t *save[nr];

Can you adjust this to avoid the VLA here? I've almost gotten all VLAs
removed from the kernel[1], and this is introducing a new one. :)

Thanks!

-Kees

[1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com

> +
> +               s = clear = t;
> +               d = t + nr;
> +               rescue = b - nr;
> +               if (dir == SM_UP) {
> +                       swap(s, d);
> +                       swap(clear, rescue);
> +               }
> +               memcpy(save, uniscr->lines + rescue, nr * sizeof(*save));
> +               memmove(uniscr->lines + d, uniscr->lines + s,
> +                       (b - t - nr) * sizeof(*uniscr->lines));
> +               memcpy(uniscr->lines + clear, save, nr * sizeof(*save));
> +               vc_uniscr_clear_lines(vc, clear, nr);
> +       }
> +}


-- 
Kees Cook
Pixel Security