From: Greg KH <email@example.com> To: Martin Hostettler <firstname.lastname@example.org>, Tetsuo Handa <email@example.com>, firstname.lastname@example.org, Peilin Ye <email@example.com>, syzbot <firstname.lastname@example.org>, email@example.com, firstname.lastname@example.org, email@example.com, Linus Torvalds <firstname.lastname@example.org>, email@example.com, firstname.lastname@example.org, email@example.com, George Kennedy <firstname.lastname@example.org> Subject: Re: [PATCH] vt_ioctl: make VT_RESIZEX behave like VT_RESIZE Date: Tue, 29 Sep 2020 17:10:40 +0000 [thread overview] Message-ID: <20200929171040.GB1351851@kroah.com> (raw) In-Reply-To: <20200929165657.GS438822@phenom.ffwll.local> On Tue, Sep 29, 2020 at 06:56:57PM +0200, Daniel Vetter wrote: > On Tue, Sep 29, 2020 at 12:52:03PM +0200, Martin Hostettler wrote: > > On Tue, Sep 29, 2020 at 10:12:46AM +0900, Tetsuo Handa wrote: > > > On 2020/09/29 2:59, Martin Hostettler wrote: > > > > On Sun, Sep 27, 2020 at 08:46:30PM +0900, Tetsuo Handa wrote: > > > >> VT_RESIZEX was introduced in Linux 1.3.3, but it is unclear that what > > > >> comes to the "+ more" part, and I couldn't find a user of VT_RESIZEX. > > > >> > > > > > > > > It seems this is/was used by "svgatextmode" which seems to be at > > > > http://www.ibiblio.org/pub/Linux/utils/console/ > > > > > > > > Not sure if that kind of software still has a chance to work nowadays. > > > > > > > > > > Thanks for the information. > > > > > > It seems that v.v_vlin = curr_textmode->VDisplay / (MOFLG_ISSET(curr_textmode, ATTR_DOUBLESCAN) ? 2 : 1) > > > and v.v_clin = curr_textmode->FontHeight . Thus, v.v_clin is font's height and seems to be non-zero. > > > But according to https://bugs.gentoo.org/19485 , people are using kernel framebuffer instead. > > > > > > > Yes, this seems to be from pre framebuffer times. > > > > Back in the days "svga" was the wording you got for "pokes svga card > > hardware registers from userspace drivers". And textmode means font > > rendering is done via (fixed function in those times) hardware scanout > > engine. Of course having only to update 2 bytes per character was a huge > > saving early on. Likely this is also before vesa VBE was reliable. > > > > So i guess the point where this all starts going wrong allowing the X parts > > of the api to be combined with FB based rendering at all? Sounds the only > > user didn't use that combination and so it was never tested? > > > > Then again, this all relates to hardware from 20 years ago... > > Imo userspace modesetting should be burned down anywhere we can. We've > gotten away with this in drivers/gpu by just seamlessly transitioning to > kernel drivers. > > Since th only userspace we've found seems to be able to cope if this ioctl > doesn't do anything, my vote goes towards ripping it out completely and > doing nothing in there. Only question is whether we should error or fail > with a silent success: Former is safer, latter can avoid a few regression > reports since the userspace tools keep "working", and usually people don't > notice for stuff this old. It worked in drivers/gpu :-) This patch just ignores the ioctl and keeps on going, so userspace "shouldn't" notice it :) And it's in linux-next now, so all should be good. thanks, greg k-h
next prev parent reply other threads:[~2020-09-29 17:10 UTC|newest] Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-02-23 17:30 KASAN: use-after-free Read in bit_putcs syzbot 2020-09-26 2:03 ` syzbot 2020-09-26 16:25 ` Tetsuo Handa 2020-09-26 19:39 ` Peilin Ye 2020-09-27 0:25 ` Tetsuo Handa 2020-09-27 8:28 ` Tetsuo Handa 2020-09-27 9:27 ` Peilin Ye 2020-09-27 11:46 ` [PATCH] vt_ioctl: make VT_RESIZEX behave like VT_RESIZE Tetsuo Handa 2020-09-27 12:06 ` Greg KH 2020-09-28 17:59 ` Martin Hostettler 2020-09-29 1:12 ` Tetsuo Handa 2020-09-29 10:52 ` Martin Hostettler 2020-09-29 16:56 ` Daniel Vetter 2020-09-29 17:10 ` Greg KH [this message] 2021-04-11 21:43 ` Maciej W. Rozycki 2021-04-11 22:15 ` Linus Torvalds 2021-04-12 7:01 ` Daniel Vetter 2021-04-12 13:30 ` Maciej W. Rozycki
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