Hi Am 17.04.23 um 13:32 schrieb Sui Jingfeng:
The fbdev test of IGT may write after EOF, which lead to out-of-bound access for the drm drivers using fbdev-generic. For example, on a x86 + aspeed bmc card platform, with a 1680x1050 resolution display, running fbdev test if IGT 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 direct reason is that damage rectange computed by drm_fb_helper_memory_range_to_clip() does not guaranteed to be in-bound. It is already results in workaround code populate to elsewhere. Another reason is that exposing a larger buffer size than the actual needed help to trigger this bug intrinsic in drm_fb_helper_memory_range_to_clip(). Others fbdev emulation solutions write to the GEM buffer directly, they won't reproduce this bug because the .fb_dirty function callback do not being hooked, so no chance is given to drm_fb_helper_memory_range_to_clip() to generate a out-of-bound when drm_fb_helper_sys_write() is called. This patch break the trigger condition of this bug by shrinking the shadow buffer size to sizes->surface_height * buffer->fb->pitches[0]. Fixes: '8fbc9af55de0 ("drm/fbdev-generic: Set screen size to size of GEM buffer")' Signed-off-by: Sui Jingfeng <suijingfeng@xxxxxxxxxxx> --- drivers/gpu/drm/drm_fbdev_generic.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/gpu/drm/drm_fbdev_generic.c b/drivers/gpu/drm/drm_fbdev_generic.c index 8e5148bf40bb..b057cfbba938 100644 --- a/drivers/gpu/drm/drm_fbdev_generic.c +++ b/drivers/gpu/drm/drm_fbdev_generic.c @@ -94,7 +94,7 @@ static int drm_fbdev_generic_helper_fb_probe(struct drm_fb_helper *fb_helper, fb_helper->buffer = buffer; fb_helper->fb = buffer->fb;- screen_size = buffer->gem->size;+ screen_size = sizes->surface_height * buffer->fb->pitches[0];
Reviewed-by: Thomas Zimmermann <tzimmermann@xxxxxxx> Thanks a lot for the bugfix. Best regards Thomas
screen_buffer = vzalloc(screen_size);
if (!screen_buffer) {
ret = -ENOMEM;
-- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Maxfeldstr. 5, 90409 Nürnberg, Germany (HRB 36809, AG Nürnberg) Geschäftsführer: Ivo Totev
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