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MID_RHS_MATCH_FROM(0.00)[]; internal_greylist_whitelist(0.00)[2a07:de40:b281:104:10:150:64:97]; RECEIVED_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:106:10:150:64:167:received]; RCPT_COUNT_SEVEN(0.00)[11]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:mid,suse.de:dkim,suse.com:url,imap1.dmz-prg2.suse.org:rdns,imap1.dmz-prg2.suse.org:helo] X-Rspamd-Server: rspamd1.dmz-prg2.suse.org X-Spam-Flag: NO Hi Am 18.05.26 um 09:17 schrieb w15303746062@163.com: > From: Mingyu Wang <25181214217@stu.xidian.edu.cn> > > When vmwgfx is configured to use VKMS for vblank simulation, it relies > on drm_calc_timestamping_constants() to calculate the frame duration > (vblank->framedur_ns). > > However, Fuzzers (like Syzkaller) can submit extremely malicious > display modes through DRM_IOCTL_MODE_SETCRTC. If the user-space passes > a mode with a massive pixel clock (crtc_clock) and small resolution > (htotal/vtotal), the integer division in drm_calc_timestamping_constants() > truncates the result to 0. > > Consequently, vmw_vkms_enable_vblank() blindly sets the hrtimer period > to 0. When the timer is started, it fires instantly and continuously. > Because hrtimer_forward_now() cannot advance time for a 0-period, > the overrun value skyrockets, locking the CPU in an infinite hard-IRQ > loop (vkms_vblank_simulate() -> HRTIMER_RESTART). > > This completely starves the CPU, leading to massive RCU stalls and > blocking other essential tasks (like jbd2 and writeback workers) > indefinitely: > > [ C1] vkms_vblank_simulate: vblank timer overrun > ... > INFO: task kworker/u18:2:50 blocked for more than 143 seconds. > Workqueue: writeback wb_workfn (flush-8:0) > Call Trace: > > __schedule+0x1044/0x5bb0 > wbt_wait+0x1c8/0x3b0 > blk_mq_submit_bio+0x29fa/0x31f0 > submit_bio_noacct+0xca7/0x1f90 > ext4_bio_write_folio+0x95a/0x1d10 > ... > > NMI backtrace for cpu 1 > Call Trace: > > vkms_vblank_simulate+0x8f/0x390 > __hrtimer_run_queues+0x1f5/0xb30 > hrtimer_interrupt+0x39a/0x880 > > Fix this DoS vulnerability by adding a defensive sanity check in > vmw_vkms_enable_vblank() to reject a 0-ns frame duration, allowing > DRM core to gracefully fallback/reject the mode without crashing. > > Fixes: cd2eb57df1b8 ("drm/vmwgfx: Implement virtual kms") > Cc: stable@vger.kernel.org > Signed-off-by: Mingyu Wang <25181214217@stu.xidian.edu.cn> > --- > drivers/gpu/drm/vmwgfx/vmwgfx_vkms.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_vkms.c b/drivers/gpu/drm/vmwgfx/vmwgfx_vkms.c > index 5abd7f5ad2db..b3950ae424f3 100644 > --- a/drivers/gpu/drm/vmwgfx/vmwgfx_vkms.c > +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_vkms.c > @@ -288,6 +288,16 @@ vmw_vkms_enable_vblank(struct drm_crtc *crtc) > > drm_calc_timestamping_constants(crtc, &crtc->mode); > > + /* > + * DEFENSIVE CHECK: > + * drm_calc_timestamping_constants() can calculate a framedur_ns > + * of 0 if user-space provides a malicious mode with a huge > + * crtc_clock and small htotal/vtotal due to integer division > + * truncation. Prevent hrtimer interrupt storms by refusing such modes. > + */ > + if (WARN_ON_ONCE(vblank->framedur_ns == 0)) > + return -EINVAL; This code does no longer exist in the development tree (i.e., drm-misc). Although the new implementation might have a similar issue. Best regards Thomas > + > hrtimer_setup(&du->vkms.timer, &vmw_vkms_vblank_simulate, CLOCK_MONOTONIC, > HRTIMER_MODE_REL); > du->vkms.period_ns = ktime_set(0, vblank->framedur_ns); -- -- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com GF: Jochen Jaser, Andrew McDonald, Werner Knoblich, (HRB 36809, AG Nürnberg)