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->dmub_srv will de NULL if the ASIC does not support DMUB, which is
tested in dm_dmub_sw_init.

However, it will be dereferenced in dmub_hw_lock_mgr_cmd if
should_use_dmub_lock returns true.

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

Fix this by checking for dmub_srv in should_use_dmub_lock.

[   37.440832] BUG: kernel NULL pointer dereference, address: 0000000000000058
[   37.447808] #PF: supervisor read access in kernel mode
[   37.452959] #PF: error_code(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 Google_Morphius.13434.858.0 10/26/2023
[   37.487103] RIP: 0010:dmub_hw_lock_mgr_cmd+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]  ? __die_body+0x66/0xb0
[   37.580756]  ? page_fault_oops+0x3e7/0x4a0
[   37.584861]  ? exc_page_fault+0x3e/0xe0
[   37.588706]  ? exc_page_fault+0x5c/0xe0
[   37.592550]  ? asm_exc_page_fault+0x22/0x30
[   37.596742]  ? dmub_hw_lock_mgr_cmd+0x77/0xb0
[   37.601107]  dcn10_cursor_lock+0x1e1/0x240
[   37.605211]  program_cursor_attributes+0x81/0x190
[   37.609923]  commit_planes_for_stream+0x998/0x1ef0
[   37.614722]  update_planes_and_stream_v2+0x41e/0x5c0
[   37.619703]  dc_update_planes_and_stream+0x78/0x140
[   37.624588]  amdgpu_dm_atomic_commit_tail+0x4362/0x49f0
[   37.629832]  ? srso_return_thunk+0x5/0x5f
[   37.633847]  ? mark_held_locks+0x6d/0xd0
[   37.637774]  ? _raw_spin_unlock_irq+0x24/0x50
[   37.642135]  ? srso_return_thunk+0x5/0x5f
[   37.646148]  ? lockdep_hardirqs_on+0x95/0x150
[   37.650510]  ? srso_return_thunk+0x5/0x5f
[   37.654522]  ? _raw_spin_unlock_irq+0x2f/0x50
[   37.658883]  ? srso_return_thunk+0x5/0x5f
[   37.662897]  ? wait_for_common+0x186/0x1c0
[   37.666998]  ? srso_return_thunk+0x5/0x5f
[   37.671009]  ? drm_crtc_next_vblank_start+0xc3/0x170
[   37.675983]  commit_tail+0xf5/0x1c0
[   37.679478]  drm_atomic_helper_commit+0x2a2/0x2b0
[   37.684186]  drm_atomic_commit+0xd6/0x100
[   37.688199]  ? __cfi___drm_printfn_info+0x10/0x10
[   37.692911]  drm_atomic_helper_update_plane+0xe5/0x130
[   37.698054]  drm_mode_cursor_common+0x501/0x670
[   37.702600]  ? __cfi_drm_mode_cursor_ioctl+0x10/0x10
[   37.707572]  drm_mode_cursor_ioctl+0x48/0x70
[   37.711851]  drm_ioctl_kernel+0xf2/0x150
[   37.715781]  drm_ioctl+0x363/0x590
[   37.719189]  ? __cfi_drm_mode_cursor_ioctl+0x10/0x10
[   37.724165]  amdgpu_drm_ioctl+0x41/0x80
[   37.728013]  __se_sys_ioctl+0x7f/0xd0
[   37.731685]  do_syscall_64+0x87/0x100
[   37.735355]  ? vma_end_read+0x12/0xe0
[   37.739024]  ? srso_return_thunk+0x5/0x5f
[   37.743041]  ? find_held_lock+0x47/0xf0
[   37.746884]  ? vma_end_read+0x12/0xe0
[   37.750552]  ? srso_return_thunk+0x5/0
---truncated---
CVSS v3.1: 5.5