From: Sui Jingfeng suijingfeng@loongson.cn
[ Upstream commit c8687694bb1f5c48134f152f8c5c2e53483eb99d ]
The fbdev test of IGT may write after EOF, which lead to out-of-bound access for drm drivers with 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 is 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 still 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)
Signed-off-by: Sui Jingfeng suijingfeng@loongson.cn Fixes: aa15c677cc34 ("drm/fb-helper: Fix vertical damage clipping") Reviewed-by: Thomas Zimmermann tzimmermann@suse.de Tested-by: Geert Uytterhoeven geert+renesas@glider.be Link: https://lore.kernel.org/dri-devel/ad44df29-3241-0d9e-e708-b0338bf3c623@189.c... Signed-off-by: Thomas Zimmermann tzimmermann@suse.de Link: https://patchwork.freedesktop.org/patch/msgid/20230420030500.1578756-1-suiji... Signed-off-by: Sasha Levin sashal@kernel.org --- 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 2fe8349be0995..2a4e9fea03dd7 100644 --- a/drivers/gpu/drm/drm_fb_helper.c +++ b/drivers/gpu/drm/drm_fb_helper.c @@ -625,19 +625,27 @@ 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);