arm64: Don't call NULL in do_compat_alignment_fixup()

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

arm64: Don't call NULL in do_compat_alignment_fixup()

do_alignment_t32_to_handler() only fixes up alignment faults for

specific instructions; it returns NULL otherwise (e.g. LDREX). When

that's the case, signal to the caller that it needs to proceed with the

regular alignment fault handling (i.e. SIGBUS). Without this patch, the

kernel panics:

Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000

Mem abort info:

ESR = 0x0000000086000006

EC = 0x21: IABT (current EL), IL = 32 bits

SET = 0, FnV = 0

EA = 0, S1PTW = 0

FSC = 0x06: level 2 translation fault

user pgtable: 4k pages, 48-bit VAs, pgdp=00000800164aa000

[0000000000000000] pgd=0800081fdbd22003, p4d=0800081fdbd22003, pud=08000815d51c6003, pmd=0000000000000000

Internal error: Oops: 0000000086000006 [#1] SMP

Modules linked in: cfg80211 rfkill xt_nat xt_tcpudp xt_conntrack nft_chain_nat xt_MASQUERADE nf_nat nf_conntrack_netlink nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 xfrm_user xfrm_algo xt_addrtype nft_compat br_netfilter veth nvme_fa>

libcrc32c crc32c_generic raid0 multipath linear dm_mod dax raid1 md_mod xhci_pci nvme xhci_hcd nvme_core t10_pi usbcore igb crc64_rocksoft crc64 crc_t10dif crct10dif_generic crct10dif_ce crct10dif_common usb_common i2c_algo_bit i2c>

CPU: 2 PID: 3932954 Comm: WPEWebProcess Not tainted 6.1.0-31-arm64 #1 Debian 6.1.128-1

Hardware name: GIGABYTE MP32-AR1-00/MP32-AR1-00, BIOS F18v (SCP: 1.08.20211002) 12/01/2021

pstate: 80400009 (Nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)

pc : 0x0

lr : do_compat_alignment_fixup+0xd8/0x3dc

sp : ffff80000f973dd0

x29: ffff80000f973dd0 x28: ffff081b42526180 x27: 0000000000000000

x26: 0000000000000000 x25: 0000000000000000 x24: 0000000000000000

x23: 0000000000000004 x22: 0000000000000000 x21: 0000000000000001

x20: 00000000e8551f00 x19: ffff80000f973eb0 x18: 0000000000000000

x17: 0000000000000000 x16: 0000000000000000 x15: 0000000000000000

x14: 0000000000000000 x13: 0000000000000000 x12: 0000000000000000

x11: 0000000000000000 x10: 0000000000000000 x9 : ffffaebc949bc488

x8 : 0000000000000000 x7 : 0000000000000000 x6 : 0000000000000000

x5 : 0000000000400000 x4 : 0000fffffffffffe x3 : 0000000000000000

x2 : ffff80000f973eb0 x1 : 00000000e8551f00 x0 : 0000000000000001

Call trace:

0x0

do_alignment_fault+0x40/0x50

do_mem_abort+0x4c/0xa0

el0_da+0x48/0xf0

el0t_32_sync_handler+0x110/0x140

el0t_32_sync+0x190/0x194

Code: bad PC value

---[ end trace 0000000000000000 ]---