[PATCH v5] drm/fbdev-generic: prohibit potential out-of-bounds access
Thomas Zimmermann
tzimmermann at suse.de
Fri Apr 21 08:09:47 UTC 2023
Hi
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:
I've merged this patch into drm-misc-fixes. Thanks for the fix.
Best regards
Thomas
>
> 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)
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