Re: [PATCH v5] drm/fbdev-generic: prohibit potential out-of-bounds access

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



Hi

Am 20.04.23 um 14:25 schrieb Geert Uytterhoeven:
Hi Thomas,

On Thu, Apr 20, 2023 at 1:10 PM Thomas Zimmermann <tzimmermann@xxxxxxx> wrote:
Am 20.04.23 um 12:04 schrieb Sui Jingfeng:
What will happen if the 'screen_size' is not page_size aligned and mmap
will mapping in the granularity of pages ?

You need to map at page granularity. If screen_size is not page-size
aligned, there's this trailing buffer that is accessible, but cannot be
displayed. But userspace has no direct way of knowing that, so let's
ignore that problem for now.

Userspace can know, if fb_fix_screeninfo.smem_{start,len} match
the actual offset and size.

Can you elaborate? How can userspace detect/compute the actually usable space?

From grep'ing fbdev drivers, smem_len appears to be a multiple of the pagesize. (?) screen_size is not exported and line_length in the fixed portion. Or can line_length change between modes? In that case it should be (yres_virtual * line_length), right?

Best regards
Thomas



Gr{oetje,eeting}s,

                         Geert


--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)

Attachment: OpenPGP_signature
Description: OpenPGP digital signature


[Index of Archives]     [Linux DRI Users]     [Linux Intel Graphics]     [Linux USB Devel]     [Video for Linux]     [Linux Audio Users]     [Yosemite News]     [Linux Kernel]     [Linux SCSI]     [XFree86]     [Linux USB Devel]     [Video for Linux]     [Linux Audio Users]     [Linux Kernel]     [Linux SCSI]     [XFree86]
  Powered by Linux