iommu/arm-smmu: Don't unregister on shutdown

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

iommu/arm-smmu: Don't unregister on shutdown

Michael Walle says he noticed the following stack trace while performing

a shutdown with "reboot -f". He suggests he got "lucky" and just hit the

correct spot for the reboot while there was a packet transmission in

flight.

Unable to handle kernel NULL pointer dereference at virtual address 0000000000000098

CPU: 0 PID: 23 Comm: kworker/0:1 Not tainted 6.1.0-rc5-00088-gf3600ff8e322 #1930

Hardware name: Kontron KBox A-230-LS (DT)

pc : iommu_get_dma_domain+0x14/0x20

lr : iommu_dma_map_page+0x9c/0x254

Call trace:

iommu_get_dma_domain+0x14/0x20

dma_map_page_attrs+0x1ec/0x250

enetc_start_xmit+0x14c/0x10b0

enetc_xmit+0x60/0xdc

dev_hard_start_xmit+0xb8/0x210

sch_direct_xmit+0x11c/0x420

__dev_queue_xmit+0x354/0xb20

ip6_finish_output2+0x280/0x5b0

__ip6_finish_output+0x15c/0x270

ip6_output+0x78/0x15c

NF_HOOK.constprop.0+0x50/0xd0

mld_sendpack+0x1bc/0x320

mld_ifc_work+0x1d8/0x4dc

process_one_work+0x1e8/0x460

worker_thread+0x178/0x534

kthread+0xe0/0xe4

ret_from_fork+0x10/0x20

Code: d503201f f9416800 d503233f d50323bf (f9404c00)

---[ end trace 0000000000000000 ]---

Kernel panic - not syncing: Oops: Fatal exception in interrupt

This appears to be reproducible when the board has a fixed IP address,

is ping flooded from another host, and "reboot -f" is used.

The following is one more manifestation of the issue:

$ reboot -f

kvm: exiting hardware virtualization

cfg80211: failed to load regulatory.db

arm-smmu 5000000.iommu: disabling translation

sdhci-esdhc 2140000.mmc: Removing from iommu group 11

sdhci-esdhc 2150000.mmc: Removing from iommu group 12

fsl-edma 22c0000.dma-controller: Removing from iommu group 17

dwc3 3100000.usb: Removing from iommu group 9

dwc3 3110000.usb: Removing from iommu group 10

ahci-qoriq 3200000.sata: Removing from iommu group 2

fsl-qdma 8380000.dma-controller: Removing from iommu group 20

platform f080000.display: Removing from iommu group 0

etnaviv-gpu f0c0000.gpu: Removing from iommu group 1

etnaviv etnaviv: Removing from iommu group 1

caam_jr 8010000.jr: Removing from iommu group 13

caam_jr 8020000.jr: Removing from iommu group 14

caam_jr 8030000.jr: Removing from iommu group 15

caam_jr 8040000.jr: Removing from iommu group 16

fsl_enetc 0000:00:00.0: Removing from iommu group 4

arm-smmu 5000000.iommu: Blocked unknown Stream ID 0x429; boot with "arm-smmu.disable_bypass=0" to allow, but this may have security implications

arm-smmu 5000000.iommu: GFSR 0x80000002, GFSYNR0 0x00000002, GFSYNR1 0x00000429, GFSYNR2 0x00000000

fsl_enetc 0000:00:00.1: Removing from iommu group 5

arm-smmu 5000000.iommu: Blocked unknown Stream ID 0x429; boot with "arm-smmu.disable_bypass=0" to allow, but this may have security implications

arm-smmu 5000000.iommu: GFSR 0x80000002, GFSYNR0 0x00000002, GFSYNR1 0x00000429, GFSYNR2 0x00000000

arm-smmu 5000000.iommu: Blocked unknown Stream ID 0x429; boot with "arm-smmu.disable_bypass=0" to allow, but this may have security implications

arm-smmu 5000000.iommu: GFSR 0x80000002, GFSYNR0 0x00000000, GFSYNR1 0x00000429, GFSYNR2 0x00000000

fsl_enetc 0000:00:00.2: Removing from iommu group 6

fsl_enetc_mdio 0000:00:00.3: Removing from iommu group 8

mscc_felix 0000:00:00.5: Removing from iommu group 3

fsl_enetc 0000:00:00.6: Removing from iommu group 7

pcieport 0001:00:00.0: Removing from iommu group 18

arm-smmu 5000000.iommu: Blocked unknown Stream ID 0x429; boot with "arm-smmu.disable_bypass=0" to allow, but this may have security implications

arm-smmu 5000000.iommu: GFSR 0x00000002, GFSYNR0 0x00000000, GFSYNR1 0x00000429, GFSYNR2 0x00000000

pcieport 0002:00:00.0: Removing from iommu group 19

Unable to handle kernel NULL pointer dereference at virtual address 00000000000000a8

pc : iommu_get_dma_domain+0x14/0x20

lr : iommu_dma_unmap_page+0x38/0xe0

Call trace:

iommu_get_dma_domain+0x14/0x20

dma_unmap_page_attrs+0x38/0x1d0

en

---truncated---