[Intel-gfx] drm_modes: signed integer overflow

[Ville Syrjälä]

On Wed, Oct 21, 2020 at 08:13:43PM -0700, Randy Dunlap wrote:
> Hi,
> 
> With linux-next 20201021, when booting up, I am seeing this:
> 
> [    0.560896] UBSAN: signed-integer-overflow in ../drivers/gpu/drm/drm_modes.c:765:20
> [    0.560903] 2376000 * 1000 cannot be represented in type 'int'

Dang. Didn't realize these new crazy >8k modes have dotclocks reaching
almost 6 GHz, which would overflow even u32. I guess we'll switch to
64bit maths. Now I wonder how many other places can hit this overflow
in practice...

> [    0.560909] CPU: 3 PID: 7 Comm: kworker/u16:0 Not tainted 5.9.0-next-20201021 #2
> [    0.560914] Hardware name: TOSHIBA PORTEGE R835/Portable PC, BIOS Version 4.10   01/08/2013
> [    0.560924] Workqueue: events_unbound async_run_entry_fn
> 
> [    0.560930] Call Trace:
> [    0.560938]  dump_stack+0x5e/0x74
> [    0.560943]  ubsan_epilogue+0x9/0x45
> [    0.560948]  handle_overflow+0x8b/0x98
> [    0.560953]  ? set_track+0x3f/0xad
> [    0.560958]  __ubsan_handle_mul_overflow+0xe/0x10
> [    0.560964]  drm_mode_vrefresh+0x4a/0xbc
> [    0.560970] initcall i915_init+0x0/0x6a returned 0 after 116076 usecs
> [    0.560974] calling  cn_proc_init+0x0/0x36 @ 1
> [    0.560978]  cea_mode_alternate_clock+0x11/0x62
> [    0.560985]  drm_match_cea_mode+0xc7/0x1e7
> [    0.560987] initcall cn_proc_init+0x0/0x36 returned 0 after 3 usecs
> [    0.560990] calling  topology_sysfs_init+0x0/0x2d @ 1
> [    0.561000]  drm_mode_validate_ycbcr420+0xd/0x48
> [    0.561005]  drm_helper_probe_single_connector_modes+0x6db/0x7da
> [    0.561012]  drm_client_modeset_probe+0x225/0x143f
> [    0.561018]  ? bitmap_fold+0x8a/0x8a
> [    0.561023]  ? update_cfs_rq_load_avg+0x192/0x1a2
> [    0.561029]  __drm_fb_helper_initial_config_and_unlock+0x3f/0x5b7
> [    0.561035]  ? get_sd_balance_interval+0x1c/0x40
> [    0.561040]  drm_fb_helper_initial_config+0x48/0x4f
> [    0.561047]  intel_fbdev_initial_config+0x13/0x23
> [    0.561052]  async_run_entry_fn+0x89/0x15c
> [    0.561058]  process_one_work+0x15c/0x1f3
> [    0.561064]  worker_thread+0x1ac/0x25d
> [    0.561069]  ? process_scheduled_works+0x2e/0x2e
> [    0.561074]  kthread+0x10e/0x116
> [    0.561078]  ? kthread_parkme+0x1c/0x1c
> [    0.561083]  ret_from_fork+0x22/0x30
> [    0.561087] ================================================================================
> 
> -- 
> ~Randy
> Reported-by: Randy Dunlap <rdunlap at infradead.org>
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> Intel-gfx at lists.freedesktop.org
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-- 
Ville Syrjälä
Intel