[PATCH v5] drm/fbdev-generic: prohibit potential out-of-bounds access
Thomas Zimmermann
tzimmermann at suse.de
Thu Apr 20 07:07:04 UTC 2023
Hi
Am 20.04.23 um 09:04 schrieb Thomas Zimmermann:
> Hi,
>
> this patch looks to me good and I'd like to merge it, if no one objects.
Rereading it, I might have been too eager. What happened to the setting
of screen_size = buffer->gem->size ? It is not relevant?
Best regards
Thomas
>
> In the near future, after i915 has switched to struct drm_client, I
> intend to move DRM's deferred-I/O helpers into fbdev-generic and i915.
> Those are the two users, but they are fairly different. They can then
> both have something tailored towards their needs.
>
> Best regards
> Thomas
>
> Am 20.04.23 um 05:05 schrieb Sui Jingfeng:
>> The fbdev test of IGT may write after EOF, which lead to out-of-bound
>> access for drm drivers hire fbdev-generic. For example, run fbdev test
>> on a x86+ast2400 platform, with 1680x1050 resolution, will cause the
>> linux kernel hang with the following call trace:
>>
>> Oops: 0000 [#1] PREEMPT SMP PTI
>> [IGT] fbdev: starting subtest eof
>> Workqueue: events drm_fb_helper_damage_work [drm_kms_helper]
>> [IGT] fbdev: starting subtest nullptr
>>
>> RIP: 0010:memcpy_erms+0xa/0x20
>> RSP: 0018:ffffa17d40167d98 EFLAGS: 00010246
>> RAX: ffffa17d4eb7fa80 RBX: ffffa17d40e0aa80 RCX: 00000000000014c0
>> RDX: 0000000000001a40 RSI: ffffa17d40e0b000 RDI: ffffa17d4eb80000
>> RBP: ffffa17d40167e20 R08: 0000000000000000 R09: ffff89522ecff8c0
>> R10: ffffa17d4e4c5000 R11: 0000000000000000 R12: ffffa17d4eb7fa80
>> R13: 0000000000001a40 R14: 000000000000041a R15: ffffa17d40167e30
>> FS: 0000000000000000(0000) GS:ffff895257380000(0000)
>> knlGS:0000000000000000
>> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> CR2: ffffa17d40e0b000 CR3: 00000001eaeca006 CR4: 00000000001706e0
>> Call Trace:
>> <TASK>
>> ? drm_fbdev_generic_helper_fb_dirty+0x207/0x330 [drm_kms_helper]
>> drm_fb_helper_damage_work+0x8f/0x170 [drm_kms_helper]
>> process_one_work+0x21f/0x430
>> worker_thread+0x4e/0x3c0
>> ? __pfx_worker_thread+0x10/0x10
>> kthread+0xf4/0x120
>> ? __pfx_kthread+0x10/0x10
>> ret_from_fork+0x2c/0x50
>> </TASK>
>> CR2: ffffa17d40e0b000
>> ---[ end trace 0000000000000000 ]---
>>
>> The is because damage rectangles computed by
>> drm_fb_helper_memory_range_to_clip() function does not guaranteed to be
>> bound in the screen's active display area. Possible reasons are:
>>
>> 1) Buffers are allocated in the granularity of page size, for mmap system
>> call support. The shadow screen buffer consumed by fbdev emulation
>> may
>> also choosed be page size aligned.
>>
>> 2) The DIV_ROUND_UP() used in drm_fb_helper_memory_range_to_clip()
>> will introduce off-by-one error.
>>
>> For example, on a 16KB page size system, in order to store a 1920x1080
>> XRGB framebuffer, we need allocate 507 pages. Unfortunately, the size
>> 1920*1080*4 can not be divided exactly by 16KB.
>>
>> 1920 * 1080 * 4 = 8294400 bytes
>> 506 * 16 * 1024 = 8290304 bytes
>> 507 * 16 * 1024 = 8306688 bytes
>>
>> line_length = 1920*4 = 7680 bytes
>>
>> 507 * 16 * 1024 / 7680 = 1081.6
>>
>> off / line_length = 507 * 16 * 1024 / 7680 = 1081
>> DIV_ROUND_UP(507 * 16 * 1024, 7680) will yeild 1082
>>
>> memcpy_toio() typically issue the copy line by line, when copy the last
>> line, out-of-bound access will be happen. Because:
>>
>> 1082 * line_length = 1082 * 7680 = 8309760, and 8309760 > 8306688
>>
>> Note that userspace may stil write to the invisiable area if a larger
>> buffer than width x stride is exposed. But it is not a big issue as
>> long as there still have memory resolve the access if not drafting so
>> far.
>>
>> - Also limit the y1 (Daniel)
>> - keep fix patch it to minimal (Daniel)
>> - screen_size is page size aligned because of it need mmap (Thomas)
>> - Adding fixes tag (Thomas)
>>
>> Fixes: aa15c677cc34 ("drm/fb-helper: Fix vertical damage clipping")
>>
>> Signed-off-by: Sui Jingfeng <suijingfeng at loongson.cn>
>> Reviewed-by: Thomas Zimmermann <tzimmermann at suse.de>
>> Tested-by: Geert Uytterhoeven <geert+renesas at glider.be>
>> Link:
>> https://lore.kernel.org/dri-devel/ad44df29-3241-0d9e-e708-b0338bf3c623@189.cn/
>> ---
>> drivers/gpu/drm/drm_fb_helper.c | 16 ++++++++++++----
>> 1 file changed, 12 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/drm_fb_helper.c
>> b/drivers/gpu/drm/drm_fb_helper.c
>> index 64458982be40..6bb1b8b27d7a 100644
>> --- a/drivers/gpu/drm/drm_fb_helper.c
>> +++ b/drivers/gpu/drm/drm_fb_helper.c
>> @@ -641,19 +641,27 @@ static void drm_fb_helper_damage(struct
>> drm_fb_helper *helper, u32 x, u32 y,
>> static void drm_fb_helper_memory_range_to_clip(struct fb_info *info,
>> off_t off, size_t len,
>> struct drm_rect *clip)
>> {
>> + u32 line_length = info->fix.line_length;
>> + u32 fb_height = info->var.yres;
>> off_t end = off + len;
>> u32 x1 = 0;
>> - u32 y1 = off / info->fix.line_length;
>> + u32 y1 = off / line_length;
>> u32 x2 = info->var.xres;
>> - u32 y2 = DIV_ROUND_UP(end, info->fix.line_length);
>> + u32 y2 = DIV_ROUND_UP(end, line_length);
>> +
>> + /* Don't allow any of them beyond the bottom bound of display
>> area */
>> + if (y1 > fb_height)
>> + y1 = fb_height;
>> + if (y2 > fb_height)
>> + y2 = fb_height;
>> if ((y2 - y1) == 1) {
>> /*
>> * We've only written to a single scanline. Try to reduce
>> * the number of horizontal pixels that need an update.
>> */
>> - off_t bit_off = (off % info->fix.line_length) * 8;
>> - off_t bit_end = (end % info->fix.line_length) * 8;
>> + off_t bit_off = (off % line_length) * 8;
>> + off_t bit_end = (end % line_length) * 8;
>> x1 = bit_off / info->var.bits_per_pixel;
>> x2 = DIV_ROUND_UP(bit_end, info->var.bits_per_pixel);
>
--
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)
-------------- next part --------------
A non-text attachment was scrubbed...
Name: OpenPGP_signature
Type: application/pgp-signature
Size: 840 bytes
Desc: OpenPGP digital signature
URL: <https://lists.freedesktop.org/archives/dri-devel/attachments/20230420/af0a43a9/attachment.sig>
More information about the dri-devel
mailing list