linux-kernel - Re: [PATCH v3 0/5] console: Miscellaneous clean-ups, do not use FNTCHARCNT() in fbcon.c

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20201117062142.GA28766@PWN>
Date:   Tue, 17 Nov 2020 01:21:42 -0500
From:   Peilin Ye <yepeilin.cs@...il.com>
To:     Daniel Vetter <daniel@...ll.ch>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Daniel Vetter <daniel@...ll.ch>,
        Jiri Slaby <jirislaby@...nel.org>,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-fbdev@...r.kernel.org
Subject: Re: [PATCH v3 0/5] console: Miscellaneous clean-ups, do not use
 FNTCHARCNT() in fbcon.c

On Mon, Nov 16, 2020 at 11:09:49AM +0100, Daniel Vetter wrote:
> On Sat, Nov 14, 2020 at 07:47:16AM -0500, Peilin Ye wrote:
> > On Sat, Nov 14, 2020 at 01:22:22PM +0100, Greg Kroah-Hartman wrote:
> > > On Sat, Nov 14, 2020 at 01:18:06PM +0100, Greg Kroah-Hartman wrote:
> > > > On Sat, Nov 14, 2020 at 03:10:21AM -0500, Peilin Ye wrote:
> > > > > Thanks for reviewing!  Questions about the last patch [5/5] though, it
> > > > > depends on the following assumption:
> > > > > 
> > > > > """
> > > > > For each console `idx`, `vc_cons[idx].d->vc_font.data` and
> > > > > `fb_display[idx].fontdata` always point to the same buffer.
> > > > > """
> > > > > 
> > > > > Is this true?  I think it is true by grepping for `fontdata`.  I also
> > > > > noticed that fbcon.c is using `vc->vc_font.data` and `p->fontdata`
> > > > > interchangeably, see fbcon_get_requirement():
> > > > > 
> > > > > 		vc = vc_cons[fg_console].d;
> > > > > 		[...]
> > > > > 			p = &fb_display[fg_console];
> > > > > 			caps->x = 1 << (vc->vc_font.width - 1);
> > > > > 					^^^^^^^^^^^
> > > > > 			caps->y = 1 << (vc->vc_font.height - 1);
> > > > > 					^^^^^^^^^^^
> > > > > 			caps->len = (p->userfont) ?
> > > > > 				FNTCHARCNT(p->fontdata) : 256;
> > > > > 					   ^^^^^^^^^^^
> > > > > 
> > > > > If it is true, then what is the point of using `fontdata` in `struct
> > > > > fbcon_display`?  Just for the `userfont` flag?  Should we delete
> > > > > `fontdata`, when we no longer need the `userfont` flag?
> > > > 
> > > > Yes, after a quick look, I think your analysis here is correct.  So if
> > > > you can delete that, it would be nice if possible.
> > 
> > I see, at the moment we still need `userfont` for refcount handling, I
> > will try to delete both `fontdata` and `userfont` after refcount is
> > taken care of.
> 
> +1 on sunsetting fondata. I think there's a bunch of these in fbcon code,
> because the console subsystem is older than the standard "allow drivers to
> embed the subsystem struct into their own private struct" subclassing
> model. So lots of global arrays indexed by the console id :-/

Yeah, I saw your comments about registered_fb[] :(

> We're also trying to start some kind of test suite for fbdev chardev ioctl
> interface in the gpu test suite. fbcon tests are maybe more related to
> tty/vt, and I have no idea whether anything exists there already.
> 
> But if you want to do some automated testcases for fbcon and there's
> absolutely no other home for them, the gpu test suite might be an option
> of last resort too:
> 
> https://dri.freedesktop.org/docs/drm/gpu/drm-uapi.html#testing-and-validation

Oh, I didn't know about igt-gpu-tools, thanks for the pointer!  Now,
since charcount is taken care of, and font_desc now contains all fields
of console_font, I think it is a good time to replace console_font with
font_desc in vc_data.  Then we can get rid of FNTSUM(), FNTSIZE(), then
(finally) REFCOUNT().

I will start working on vc_data, after done enough testing on [5/5],
ofc. Thanks,

Peilin Ye