In the Linux kernel, the following vulnerability has been resolved:

drm/display/dpmst: Add protection against 0 vcpi

When releasing a timeslot there is a slight chance we may end up with the wrong payload mask due to overflow if the delayeddestroywork ends up coming into play after a DP 2.1 monitor gets disconnected which causes vcpi to become 0 then we try to make the payload = ~BIT(vcpi - 1) which is a negative shift. VCPI id should never really be 0 hence skip changing the payload mask if VCPI is 0.

Otherwise it leads to <7> [515.287237] xe 0000:03:00.0: [drm:drmdpmstgetportmalloc [drmdisplayhelper]] port ffff888126ce9000 (3) <4> [515.287267] -----------[ cut here ]----------- <3> [515.287268] UBSAN: shift-out-of-bounds in ../drivers/gpu/drm/display/drmdpmsttopology.c:4575:36 <3> [515.287271] shift exponent -1 is negative <4> [515.287275] CPU: 7 UID: 0 PID: 3108 Comm: kworker/u64:33 Tainted: G S U 6.17.0-rc6-lgci-xe-xe-3795-3e79699fa1b216e92+ #1 PREEMPT(voluntary) <4> [515.287279] Tainted: [S]=CPUOUTOFSPEC, [U]=USER <4> [515.287279] Hardware name: ASUS System Product Name/PRIME Z790-P WIFI, BIOS 1645 03/15/2024 <4> [515.287281] Workqueue: drmdpmstwq drmdpdelayeddestroywork [drmdisplayhelper] <4> [515.287303] Call Trace: <4> [515.287304] <TASK> <4> [515.287306] dumpstacklvl+0xc1/0xf0 <4> [515.287313] dumpstack+0x10/0x20 <4> [515.287316] ubsanhandleshiftoutofbounds+0x133/0x2e0 <4> [515.287324] ? drmatomicgetprivateobjstate+0x186/0x1d0 <4> [515.287333] drmdpatomicreleasetimeslots.cold+0x17/0x3d [drmdisplayhelper] <4> [515.287355] mstconnectoratomiccheck+0x159/0x180 [xe] <4> [515.287546] drmatomichelpercheckmodeset+0x4d9/0xfa0 <4> [515.287550] ? wwmutexlock.constprop.0+0x6f/0x1a60 <4> [515.287562] intelatomiccheck+0x119/0x2b80 [xe] <4> [515.287740] ? findheldlock+0x31/0x90 <4> [515.287747] ? lockrelease+0xce/0x2a0 <4> [515.287754] drmatomiccheckonly+0x6a2/0xb40 <4> [515.287758] ? drmatomicaddaffectedconnectors+0x12b/0x140 <4> [515.287765] drmatomiccommit+0x6e/0xf0 <4> [515.287766] ? pfxdrmprintfninfo+0x10/0x10 <4> [515.287774] drmclientmodesetcommitatomic+0x25c/0x2b0 <4> [515.287794] drmclientmodesetcommitlocked+0x60/0x1b0 <4> [515.287795] ? mutexlocknested+0x1b/0x30 <4> [515.287801] drmclientmodesetcommit+0x26/0x50 <4> [515.287804] drmfbhelperrestorefbdevmodeunlocked+0xdc/0x110 <4> [515.287810] drmfbhelperhotplugevent+0x120/0x140 <4> [515.287814] drmfbdevclienthotplug+0x28/0xd0 <4> [515.287819] drmclienthotplug+0x6c/0xf0 <4> [515.287824] drmclientdevhotplug+0x9e/0xd0 <4> [515.287829] drmkmshelperhotplugevent+0x1a/0x30 <4> [515.287834] drmdpdelayeddestroywork+0x3df/0x410 [drmdisplayhelper] <4> [515.287861] processonework+0x22b/0x6f0 <4> [515.287874] workerthread+0x1e8/0x3d0 <4> [515.287879] ? pfxworkerthread+0x10/0x10 <4> [515.287882] kthread+0x11c/0x250 <4> [515.287886] ? pfxkthread+0x10/0x10 <4> [515.287890] retfromfork+0x2d7/0x310 <4> [515.287894] ? pfxkthread+0x10/0x10 <4> [515.287897] retfromforkasm+0x1a/0x30