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

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Date:   Tue, 10 Jul 2018 23:39:39 -0400
From:   Nicolas Pitre <nicolas.pitre@...aro.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Nicolas Pitre <nicolas.pitre@...aro.org>,
        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

I am on vacation away from an actual keyboard until next week. Will look at it then. 

> Le 10 juill. 2018 à 20:52, Kees Cook <keescook@...omium.org> a écrit :
> 
>> 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