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

dmaengine: idxd: Ensure safe user copy of completion record

If CONFIG_HARDENED_USERCOPY is enabled, copying completion record from
event log cache to user triggers a kernel bug.

[ 1987.159822] usercopy: Kernel memory exposure attempt detected from SLUB object ‘dsa0’ (offset 74, size 31)!
[ 1987.170845] ——————[ cut here ]——————
[ 1987.176086] kernel BUG at mm/usercopy.c:102!
[ 1987.180946] invalid opcode: 0000 [#1] PREEMPT SMP NOPTI
[ 1987.186866] CPU: 17 PID: 528 Comm: kworker/17:1 Not tainted 6.8.0-rc2+ #5
[ 1987.194537] Hardware name: Intel Corporation AvenueCity/AvenueCity, BIOS BHSDCRB1.86B.2492.D03.2307181620 07/18/2023
[ 1987.206405] Workqueue: wq0.0 idxd_evl_fault_work [idxd]
[ 1987.212338] RIP: 0010:usercopy_abort+0x72/0x90
[ 1987.217381] Code: 58 65 9c 50 48 c7 c2 17 85 61 9c 57 48 c7 c7 98 fd 6b 9c 48 0f 44 d6 48 c7 c6 b3 08 62 9c 4c 89 d1 49 0f 44 f3 e8 1e 2e d5 ff <0f> 0b 49 c7 c1 9e 42 61 9c 4c 89 cf 4d 89 c8 eb a9 66 66 2e 0f 1f
[ 1987.238505] RSP: 0018:ff62f5cf20607d60 EFLAGS: 00010246
[ 1987.244423] RAX: 000000000000005f RBX: 000000000000001f RCX: 0000000000000000
[ 1987.252480] RDX: 0000000000000000 RSI: ffffffff9c61429e RDI: 00000000ffffffff
[ 1987.260538] RBP: ff62f5cf20607d78 R08: ff2a6a89ef3fffe8 R09: 00000000fffeffff
[ 1987.268595] R10: ff2a6a89eed00000 R11: 0000000000000003 R12: ff2a66934849c89a
[ 1987.276652] R13: 0000000000000001 R14: ff2a66934849c8b9 R15: ff2a66934849c899
[ 1987.284710] FS: 0000000000000000(0000) GS:ff2a66b22fe40000(0000) knlGS:0000000000000000
[ 1987.293850] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 1987.300355] CR2: 00007fe291a37000 CR3: 000000010fbd4005 CR4: 0000000000f71ef0
[ 1987.308413] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 1987.316470] DR3: 0000000000000000 DR6: 00000000fffe07f0 DR7: 0000000000000400
[ 1987.324527] PKRU: 55555554
[ 1987.327622] Call Trace:
[ 1987.330424] <TASK>
[ 1987.332826] ? show_regs+0x6e/0x80
[ 1987.336703] ? die+0x3c/0xa0
[ 1987.339988] ? do_trap+0xd4/0xf0
[ 1987.343662] ? do_error_trap+0x75/0xa0
[ 1987.347922] ? usercopy_abort+0x72/0x90
[ 1987.352277] ? exc_invalid_op+0x57/0x80
[ 1987.356634] ? usercopy_abort+0x72/0x90
[ 1987.360988] ? asm_exc_invalid_op+0x1f/0x30
[ 1987.365734] ? usercopy_abort+0x72/0x90
[ 1987.370088] __check_heap_object+0xb7/0xd0
[ 1987.374739] __check_object_size+0x175/0x2d0
[ 1987.379588] idxd_copy_cr+0xa9/0x130 [idxd]
[ 1987.384341] idxd_evl_fault_work+0x127/0x390 [idxd]
[ 1987.389878] process_one_work+0x13e/0x300
[ 1987.394435] ? __pfx_worker_thread+0x10/0x10
[ 1987.399284] worker_thread+0x2f7/0x420
[ 1987.403544] ? _raw_spin_unlock_irqrestore+0x2b/0x50
[ 1987.409171] ? __pfx_worker_thread+0x10/0x10
[ 1987.414019] kthread+0x107/0x140
[ 1987.417693] ? __pfx_kthread+0x10/0x10
[ 1987.421954] ret_from_fork+0x3d/0x60
[ 1987.426019] ? __pfx_kthread+0x10/0x10
[ 1987.430281] ret_from_fork_asm+0x1b/0x30
[ 1987.434744] </TASK>

The issue arises because event log cache is created using
kmem_cache_create() which is not suitable for user copy.

Fix the issue by creating event log cache with
kmem_cache_create_usercopy(), ensuring safe user copy.