[6.4-rc6] Crash during a kexec operation (tpm_amd_is_rng_defective)

[Sachin Sant]

Following crash is observed during a kexec operation on 
IBM Power10 server:

[ 34.381548] Kernel attempted to read user page (50) - exploit attempt? (uid: 0)
[ 34.381562] BUG: Kernel NULL pointer dereference on read at 0x00000050
[ 34.381565] Faulting instruction address: 0xc0000000009db1e4
[ 34.381569] Oops: Kernel access of bad area, sig: 11 [#1]
[ 34.381572] LE PAGE_SIZE=64K MMU=Radix SMP NR_CPUS=2048 NUMA pSeries
[ 34.381576] Modules linked in: dm_mod(E) nft_fib_inet(E) nft_fib_ipv4(E) nft_fib_ipv6(E) nft_fib(E) nft_reject_inet(E) nf_reject_ipv4(E) nf_reject_ipv6(E) nft_reject(E) nft_ct(E) nft_chain_nat(E) nf_nat(E) nf_conntrack(E) nf_defrag_ipv6(E) nf_defrag_ipv4(E) bonding(E) tls(E) rfkill(E) ip_set(E) sunrpc(E) nf_tables(E) nfnetlink(E) pseries_rng(E) aes_gcm_p10_crypto(E) drm(E) drm_panel_orientation_quirks(E) xfs(E) libcrc32c(E) sd_mod(E) sr_mod(E) t10_pi(E) crc64_rocksoft_generic(E) cdrom(E) crc64_rocksoft(E) crc64(E) sg(E) ibmvscsi(E) scsi_transport_srp(E) ibmveth(E) vmx_crypto(E) fuse(E)
[ 34.381613] CPU: 18 PID: 5918 Comm: kexec Kdump: loaded Tainted: G E 6.4.0-rc6-00037-gb6dad5178cea #3
[ 34.381618] Hardware name: IBM,9080-HEX POWER10 (raw) 0x800200 0xf000006 of:IBM,FW1030.20 (NH1030_058) hv:phyp pSeries
[ 34.381621] NIP: c0000000009db1e4 LR: c0000000009db928 CTR: c0000000009eab60
[ 34.381625] REGS: c00000009742f780 TRAP: 0300 Tainted: G E (6.4.0-rc6-00037-gb6dad5178cea)
[ 34.381628] MSR: 800000000280b033 <SF,VEC,VSX,EE,FP,ME,IR,DR,RI,LE> CR: 44488884 XER: 00000001
[ 34.381638] CFAR: c0000000009db19c DAR: 0000000000000050 DSISR: 40000000 IRQMASK: 0 
[ 34.381638] GPR00: c0000000009db928 c00000009742fa20 c0000000014a1500 c0000000081d0000 
[ 34.381638] GPR04: c00000000d842c50 c00000000d842c50 0000000000000025 fffffffffffe0000 
[ 34.381638] GPR08: 0000000000000000 0000000000000000 0000000000000009 c008000000785280 
[ 34.381638] GPR12: c0000000009eab60 c00000135fab7f00 0000000000000000 0000000000000000 
[ 34.381638] GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 
[ 34.381638] GPR20: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 
[ 34.381638] GPR24: 0000000000000000 0000000000000000 0000000000000000 c000000002e21e08 
[ 34.381638] GPR28: c00000000d842c48 c000000002a02208 c00000000321c0c0 c0000000081d0000 
[ 34.381674] NIP [c0000000009db1e4] tpm_amd_is_rng_defective+0x74/0x240
[ 34.381681] LR [c0000000009db928] tpm_chip_unregister+0x138/0x160
[ 34.381685] Call Trace:
[ 34.381686] [c00000009742faa0] [c0000000009db928] tpm_chip_unregister+0x138/0x160
[ 34.381690] [c00000009742fae0] [c0000000009eab94] tpm_ibmvtpm_remove+0x34/0x130
[ 34.381695] [c00000009742fb50] [c000000000115738] vio_bus_remove+0x58/0xd0
[ 34.381701] [c00000009742fb90] [c000000000a01ecc] device_shutdown+0x21c/0x39c
[ 34.381705] [c00000009742fc20] [c0000000001a2684] kernel_restart_prepare+0x54/0x70
[ 34.381710] [c00000009742fc40] [c000000000292c48] kernel_kexec+0xa8/0x100
[ 34.381714] [c00000009742fcb0] [c0000000001a2cd4] __do_sys_reboot+0x214/0x2c0
[ 34.381718] [c00000009742fe10] [c000000000034adc] system_call_exception+0x13c/0x340
[ 34.381723] [c00000009742fe50] [c00000000000d05c] system_call_vectored_common+0x15c/0x2ec
[ 34.381729] --- interrupt: 3000 at 0x7fff9c5459f0
[ 34.381732] NIP: 00007fff9c5459f0 LR: 0000000000000000 CTR: 0000000000000000
[ 34.381735] REGS: c00000009742fe80 TRAP: 3000 Tainted: G E (6.4.0-rc6-00037-gb6dad5178cea)
[ 34.381738] MSR: 800000000280f033 <SF,VEC,VSX,EE,PR,FP,ME,IR,DR,RI,LE> CR: 42422884 XER: 00000000
[ 34.381747] IRQMASK: 0 
[ 34.381747] GPR00: 0000000000000058 00007ffffad83d70 000000012fc47f00 fffffffffee1dead 
[ 34.381747] GPR04: 0000000028121969 0000000045584543 0000000000000000 0000000000000003 
[ 34.381747] GPR08: 0000000000100000 0000000000000000 0000000000000000 0000000000000000 
[ 34.381747] GPR12: 0000000000000000 00007fff9c7bb2c0 000000012fc3f598 0000000000000000 
[ 34.381747] GPR16: ffffffffffffffff 0000000000000000 000000012fc1fcc0 0000000000000000 
[ 34.381747] GPR20: 0000000000008913 0000000000008914 000000014b891020 0000000000000003 
[ 34.381747] GPR24: 0000000000000000 0000000000000001 0000000000000003 00007ffffad83ef0 
[ 34.381747] GPR28: 000000012fc19f10 00007fff9c6419c0 000000014b891080 000000014b891040 
[ 34.381781] NIP [00007fff9c5459f0] 0x7fff9c5459f0
[ 34.381784] LR [0000000000000000] 0x0
[ 34.381786] --- interrupt: 3000
[ 34.381788] Code: 5463063e 408201c8 38210080 4e800020 60000000 60000000 60000000 7c0802a6 fbe10078 7c7f1b78 f8010090 e9230728 <e9890050> 2c2c0000 41820020 7d8903a6 
[ 34.381800] ---[ end trace 0000000000000000 ]---
[ 34.384090] pstore: backend (nvram) writing error (-1)

Git bisect points to following patch

commit bd8621ca1510e6e802df9855bdc35a04a3cfa932
    tpm: Add !tpm_amd_is_rng_defective() to the hwrng_unregister() call site

Reverting the commit allows a successful kexec operation.

- Sachin