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

iommufd: Require drivers to supply the cache_invalidate_user ops

If drivers don’t do this then iommufd will oops invalidation ioctls with
something like:

Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000
Mem abort info:

ESR = 0x0000000086000004
EC = 0x21: IABT (current EL), IL = 32 bits
SET = 0, FnV = 0
EA = 0, S1PTW = 0
FSC = 0x04: level 0 translation fault

user pgtable: 4k pages, 48-bit VAs, pgdp=0000000101059000
[0000000000000000] pgd=0000000000000000, p4d=0000000000000000
Internal error: Oops: 0000000086000004 [#1] PREEMPT SMP
Modules linked in:
CPU: 2 PID: 371 Comm: qemu-system-aar Not tainted 6.8.0-rc7-gde77230ac23a #9
Hardware name: linux,dummy-virt (DT)
pstate: 81400809 (Nzcv daif +PAN -UAO -TCO +DIT -SSBS BTYPE=-c)
pc : 0x0
lr : iommufd_hwpt_invalidate+0xa4/0x204
sp : ffff800080f3bcc0
x29: ffff800080f3bcf0 x28: ffff0000c369b300 x27: 0000000000000000
x26: 0000000000000000 x25: 0000000000000000 x24: 0000000000000000
x23: 0000000000000000 x22: 00000000c1e334a0 x21: ffff0000c1e334a0
x20: ffff800080f3bd38 x19: ffff800080f3bd58 x18: 0000000000000000
x17: 0000000000000000 x16: 0000000000000000 x15: 0000ffff8240d6d8
x14: 0000000000000000 x13: 0000000000000000 x12: 0000000000000000
x11: 0000000000000000 x10: 0000000000000000 x9 : 0000000000000000
x8 : 0000001000000002 x7 : 0000fffeac1ec950 x6 : 0000000000000000
x5 : ffff800080f3bd78 x4 : 0000000000000003 x3 : 0000000000000002
x2 : 0000000000000000 x1 : ffff800080f3bcc8 x0 : ffff0000c6034d80
Call trace:
0x0
iommufd_fops_ioctl+0x154/0x274
__arm64_sys_ioctl+0xac/0xf0
invoke_syscall+0x48/0x110
el0_svc_common.constprop.0+0x40/0xe0
do_el0_svc+0x1c/0x28
el0_svc+0x34/0xb4
el0t_64_sync_handler+0x120/0x12c
el0t_64_sync+0x190/0x194

All existing drivers implement this op for nesting, this is mostly a
bisection aid.