CVE-2025-22093: drm/amd/display: avoid NPD when ASIC does not support DMUB

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

drm/amd/display: avoid NPD when ASIC does not support DMUB

ctx->dmubsrv will de NULL if the ASIC does not support DMUB, which is tested in dmdmubswinit.

However, it will be dereferenced in dmubhwlockmgrcmd if shouldusedmublock returns true.

This has been the case since dmub support has been added for PSR1.

Fix this by checking for dmubsrv in shouldusedmublock.

[ 37.440832] BUG: kernel NULL pointer dereference, address: 0000000000000058 [ 37.447808] #PF: supervisor read access in kernel mode [ 37.452959] #PF: errorcode(0x0000) - not-present page [ 37.458112] PGD 0 P4D 0 [ 37.460662] Oops: Oops: 0000 [#1] PREEMPT SMP NOPTI [ 37.465553] CPU: 2 UID: 1000 PID: 1745 Comm: DrmThread Not tainted 6.14.0-rc1-00003-gd62e938120f0 #23 99720e1cb1e0fc4773b8513150932a07de3c6e88 [ 37.478324] Hardware name: Google Morphius/Morphius, BIOS GoogleMorphius.13434.858.0 10/26/2023 [ 37.487103] RIP: 0010:dmubhwlockmgrcmd+0x77/0xb0 [ 37.492074] Code: 44 24 0e 00 00 00 00 48 c7 04 24 45 00 00 0c 40 88 74 24 0d 0f b6 02 88 44 24 0c 8b 01 89 44 24 08 85 f6 75 05 c6 44 24 0e 01 <48> 8b 7f 58 48 89 e6 ba 01 00 00 00 e8 08 3c 2a 00 65 48 8b 04 5 [ 37.510822] RSP: 0018:ffff969442853300 EFLAGS: 00010202 [ 37.516052] RAX: 0000000000000000 RBX: ffff92db03000000 RCX: ffff969442853358 [ 37.523185] RDX: ffff969442853368 RSI: 0000000000000001 RDI: 0000000000000000 [ 37.530322] RBP: 0000000000000001 R08: 00000000000004a7 R09: 00000000000004a5 [ 37.537453] R10: 0000000000000476 R11: 0000000000000062 R12: ffff92db0ade8000 [ 37.544589] R13: ffff92da01180ae0 R14: ffff92da011802a8 R15: ffff92db03000000 [ 37.551725] FS: 0000784a9cdfc6c0(0000) GS:ffff92db2af00000(0000) knlGS:0000000000000000 [ 37.559814] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 37.565562] CR2: 0000000000000058 CR3: 0000000112b1c000 CR4: 00000000003506f0 [ 37.572697] Call Trace: [ 37.575152] <TASK> [ 37.577258] ? diebody+0x66/0xb0 [ 37.580756] ? pagefaultoops+0x3e7/0x4a0 [ 37.584861] ? excpagefault+0x3e/0xe0 [ 37.588706] ? excpagefault+0x5c/0xe0 [ 37.592550] ? asmexcpagefault+0x22/0x30 [ 37.596742] ? dmubhwlockmgrcmd+0x77/0xb0 [ 37.601107] dcn10cursorlock+0x1e1/0x240 [ 37.605211] programcursorattributes+0x81/0x190 [ 37.609923] commitplanesforstream+0x998/0x1ef0 [ 37.614722] updateplanesandstreamv2+0x41e/0x5c0 [ 37.619703] dcupdateplanesandstream+0x78/0x140 [ 37.624588] amdgpudmatomiccommittail+0x4362/0x49f0 [ 37.629832] ? srsoreturnthunk+0x5/0x5f [ 37.633847] ? markheldlocks+0x6d/0xd0 [ 37.637774] ? rawspinunlockirq+0x24/0x50 [ 37.642135] ? srsoreturnthunk+0x5/0x5f [ 37.646148] ? lockdephardirqson+0x95/0x150 [ 37.650510] ? srsoreturnthunk+0x5/0x5f [ 37.654522] ? rawspinunlockirq+0x2f/0x50 [ 37.658883] ? srsoreturnthunk+0x5/0x5f [ 37.662897] ? waitforcommon+0x186/0x1c0 [ 37.666998] ? srsoreturnthunk+0x5/0x5f [ 37.671009] ? drmcrtcnextvblankstart+0xc3/0x170 [ 37.675983] committail+0xf5/0x1c0 [ 37.679478] drmatomichelpercommit+0x2a2/0x2b0 [ 37.684186] drmatomiccommit+0xd6/0x100 [ 37.688199] ? cfidrmprintfninfo+0x10/0x10 [ 37.692911] drmatomichelperupdateplane+0xe5/0x130 [ 37.698054] drmmodecursorcommon+0x501/0x670 [ 37.702600] ? cfidrmmodecursorioctl+0x10/0x10 [ 37.707572] drmmodecursorioctl+0x48/0x70 [ 37.711851] drmioctlkernel+0xf2/0x150 [ 37.715781] drmioctl+0x363/0x590 [ 37.719189] ? cfidrmmodecursorioctl+0x10/0x10 [ 37.724165] amdgpudrmioctl+0x41/0x80 [ 37.728013] sesysioctl+0x7f/0xd0 [ 37.731685] dosyscall64+0x87/0x100 [ 37.735355] ? vmaendread+0x12/0xe0 [ 37.739024] ? srsoreturnthunk+0x5/0x5f [ 37.743041] ? findheldlock+0x47/0xf0 [ 37.746884] ? vmaendread+0x12/0xe0 [ 37.750552] ? srsoreturnthunk+0x5/0 ---truncated---