Re: powernv_rng_read: Oops: Kernel access of bad area, sig: 11 [#1]

[Paul Menzel <pmenzel@molgen.mpg.de>]

Dear Madhavan, dear Jason,


Am 11.05.26 um 10:03 schrieb Paul Menzel:

> Am 11.05.26 um 09:00 schrieb Paul Menzel:
> 
>> Am 07.05.26 um 04:40 schrieb Madhavan Srinivasan:
>>>
>>> On 5/6/26 7:31 PM, Paul Menzel wrote:
>>
>>>> After a long while, on the 8335-GCA POWER8 (raw) 0x4d0200 
>>>> opal:skiboot-5.4.8-5787ad3 PowerNV, I built Linux from Linus’ master 
>>>> branch and rebooted via kexec.
>>>>
>>>> ```
>>>> [    0.000000] Linux version 7.1.0-rc2+ (pmenzel@flughafenberlinbrandenburgwillybrandt.molgen.mpg.de) (gcc (Ubuntu 11.2.0-7ubuntu2) 11.2.0, GNU ld (GNU Binutils for Ubuntu) 2.37) #3 SMP PREEMPT Wed May  6 08:50:58 CEST 2026
>>>> […]
>>>> [   17.901992] Kernel attempted to read user page (0) - exploit attempt? (uid: 0)
>>>> [   17.902011] BUG: Kernel NULL pointer dereference on read at 0x00000000
>>>> [   17.902018] Faulting instruction address: 0xc0000000000e7138
>>>> [   17.902027] Oops: Kernel access of bad area, sig: 11 [#1]
>>>> [   17.902034] LE PAGE_SIZE=64K MMU=Hash  SMP NR_CPUS=2048 NUMA PowerNV
>>>> [   17.902045] Modules linked in: powernv_rng(+) bnx2x ofpart ibmpowernv bfq mdio cmdlinepart powernv_flash ipmi_powernv ipmi_devintf mtd ipmi_msghandler at24(+) vmx_crypto opal_prd sch_fq_codel nfsd parport_pc ppdev auth_rpcgss nfs_acl lp lockd grace parport sunrpc autofs4 btrfs xor libblake2b raid6_pq ast drm_shmem_helper drm_client_lib i2c_algo_bit drm_kms_helper drm ahci drm_panel_orientation_quirks libahci
>>>> [   17.902185] CPU: 147 UID: 0 PID: 2626 Comm: hwrng Not tainted 7.1.0-rc2+ #3 PREEMPTLAZY
>>>> [   17.902197] Hardware name: 8335-GCA POWER8 (raw) 0x4d0200 opal:skiboot-5.4.8-5787ad3 PowerNV
>>>> [   17.902204] NIP:  c0000000000e7138 LR: c00800001ec8013c CTR: c0000000000e70fc
>>>> [   17.902212] REGS: c000000092913c50 TRAP: 0300   Not tainted (7.1.0-rc2+)
>>>> [   17.902222] MSR:  900000000280b033 <SF,HV,VEC,VSX,EE,FP,ME,IR,DR,RI,LE>  CR: 44420220  XER: 20000000
>>>> [   17.902269] CFAR: c00800001ec8026c DAR: 0000000000000000 DSISR: 40000000 IRQMASK: 0
>>>>                GPR00: c00800001ec8013c c000000092913ef0 c000000001c18100 c00000002222d900
>>>>                GPR04: c00000002222d900 0000000000000080 0000000000000001 0000000000000000
>>>>                GPR08: 0000000000000000 c000000002212000 c0000000951e1780 c00800001ec80258
>>>>                GPR12: c0000000000e70fc c00000ffff6fd700 c0000000001d11c0 c00000001b99b9c0
>>>>                GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
>>>>                GPR20: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
>>>>                GPR24: 0000000000000000 c000000002fe6a58 0000000000000000 0000000000000000
>>>>                GPR28: c000000002fe6a20 0000000000000010 000000000000000f c00000002222d900
>>>> [   17.902406] NIP [c0000000000e7138] pnv_get_random_long+0x3c/0x114
>>>> [   17.902426] LR [c00800001ec8013c] powernv_rng_read+0x78/0xc4 [powernv_rng]
>>>> [   17.902444] Call Trace:
>>>> [   17.902448] [c000000092913ef0] [c000000092913f30] 0xc000000092913f30 (unreliable)
>>>> [   17.902463] [c000000092913f30] [c000000000decd58] hwrng_fillfn+0xd4/0x3dc
>>>> [   17.902484] [c000000092913f90] [c0000000001d1328] kthread+0x170/0x1a4
>>>> [   17.902498] [c000000092913fe0] [c00000000000d030] start_kernel_thread+0x14/0x18
>>>> [   17.902513] Code: 60000000 7d2000a6 71290010 418200bc e94d0908 812a0000 39290001 912a0000 e90d0030 3d220060 39299f00 7d08482a <e9280000> 7c0004ac e8e90000 0c070000
>>>> [   17.902569] ---[ end trace 0000000000000000 ]---
>>>> [   18.008801] pstore: backend (nvram) writing error (-1)
>>>>
>>>> [   18.015458] note: hwrng[2626] exited with irqs disabled
>>>> [   18.015483] note: hwrng[2626] exited with preempt_count 1
>>>> ```
>>>>
>>>> Please find the output of `dmesg` attached.
>>>
>>> This is from my yesterday's boot test log in my P8, did not see this 
>>> fail.
>>>
>>> root@ltcppm1:~# uname -a
>>> Linux ltcppm1.ltc.tadn.ibm.com 7.1.0-rc2-00021-gf583bd5f64d4 #1 SMP 
>>> PREEMPT Wed May  6 00:55:45 EDT 2026 ppc64le GNU/Linux
>>> root@ltcppm1:~# dmesg
>>> [    0.000000] [      T0] random: crng init done
>>> [    0.000000] [      T0] hash-mmu: Page sizes from device-tree:
>>> [    0.000000] [      T0] hash-mmu: base_shift=12: shift=12, sllp=0x0000, avpnm=0x00000000, tlbiel=1, penc=0
>>> [    0.000000] [      T0] hash-mmu: base_shift=12: shift=16, sllp=0x0000, avpnm=0x00000000, tlbiel=1, penc=7
>>> [    0.000000] [      T0] hash-mmu: base_shift=12: shift=24, sllp=0x0000, avpnm=0x00000000, tlbiel=1, penc=56
>>> [    0.000000] [      T0] hash-mmu: base_shift=16: shift=16, sllp=0x0110, avpnm=0x00000000, tlbiel=1, penc=1
>>> [    0.000000] [      T0] hash-mmu: base_shift=16: shift=24, sllp=0x0110, avpnm=0x00000000, tlbiel=1, penc=8
>>> [    0.000000] [      T0] hash-mmu: base_shift=24: shift=24, sllp=0x0100, avpnm=0x00000001, tlbiel=0, penc=0
>>> [    0.000000] [      T0] hash-mmu: base_shift=34: shift=34, sllp=0x0120, avpnm=0x000007ff, tlbiel=0, penc=3
>>> [    0.000000] [      T0] Enabling pkeys with max key count 32
>>> [    0.000000] [      T0] Activating Kernel Userspace Access Prevention
>>> [    0.000000] [      T0] Activating Kernel Userspace Execution Prevention
>>> [    0.000000] [      T0] hash-mmu: Page orders: linear mapping = 24, virtual = 16, io = 16, vmemmap = 24
>>> [    0.000000] [      T0] hash-mmu: Using 1TB segments
>>> [    0.000000] [      T0] hash-mmu: Initializing hash mmu with SLB
>>> [    0.000000] [      T0] Linux version 7.1.0-rc2-00021-gf583bd5f64d4 (root@ltcppm1.ltc.tadn.ibm.com) (gcc (GCC) 16.1.1 20260501 (Red Hat 16.1.1-1), GNU ld version 2.46-1.fc44) #1 SMP PREEMPT Wed May  6 00:55:45 EDT 2026
>>> [    0.000000] [      T0] OF: reserved mem: 0x0000000039c00000..0x000000003b6801ff (27136 KiB) map non-reusable ibm,firmware-allocs-memory@39c00000
>>> [    0.000000] [      T0] OF: reserved mem: 0x0000000800000000..0x0000000800e801ff (14848 KiB) map non-reusable ibm,firmware-allocs-memory@800000000
>>> [    0.000000] [      T0] OF: reserved mem: 0x0000001000000000..0x0000001000dc01ff (14080 KiB) map non-reusable ibm,firmware-allocs-memory@1000000000
>>> [    0.000000] [      T0] OF: reserved mem: 0x0000001800000000..0x0000001800e801ff (14848 KiB) map non-reusable ibm,firmware-allocs-memory@1800000000
>>> [    0.000000] [      T0] OF: reserved mem: 0x0000000030000000..0x00000000302fffff (3072 KiB) map non-reusable ibm,firmware-code@30000000
>>> [    0.000000] [      T0] OF: reserved mem: 0x0000000031000000..0x0000000031bfffff (12288 KiB) map non-reusable ibm,firmware-data@31000000
>>> [    0.000000] [      T0] OF: reserved mem: 0x0000000030300000..0x0000000030ffffff (13312 KiB) map non-reusable ibm,firmware-heap@30300000
>>> [    0.000000] [      T0] OF: reserved mem: 0x0000000031c00000..0x0000000033fdffff (36736 KiB) map non-reusable ibm,firmware-stacks@31c00000
>>> [    0.000000] [      T0] OF: reserved mem: 0x0000001ffd510000..0x0000001ffd69ffff (1600 KiB) map non-reusable ibm,hbrt-code-image@1ffd510000
>>> [    0.000000] [      T0] OF: reserved mem: 0x0000001ffd6a0000..0x0000001ffd6fffff (384 KiB) map non-reusable ibm,hbrt-target-image@1ffd6a0000
>>> [    0.000000] [      T0] OF: reserved mem: 0x0000001ffd700000..0x0000001ffd7fffff (1024 KiB) map non-reusable ibm,hbrt-vpd-image@1ffd700000
>>> [    0.000000] [      T0] OF: reserved mem: 0x0000001ffda00000..0x0000001ffdafffff (1024 KiB) map non-reusable ibm,slw-image@1ffda00000
>>> [    0.000000] [      T0] OF: reserved mem: 0x0000001ffde00000..0x0000001ffdefffff (1024 KiB) map non-reusable ibm,slw-image@1ffde00000
>>> [    0.000000] [      T0] OF: reserved mem: 0x0000001ffe200000..0x0000001ffe2fffff (1024 KiB) map non-reusable ibm,slw-image@1ffe200000
>>> [    0.000000] [      T0] OF: reserved mem: 0x0000001ffe600000..0x0000001ffe6fffff (1024 KiB) map non-reusable ibm,slw-image@1ffe600000
>>> [    0.000000] [      T0] Found initrd at 0xc000000006a40000:0xc00000000815ae9e
>>> [    0.000000] [      T0] Hardware name: 8247-22L POWER8E (raw) 0x4b0201 opal:skiboot-v5.4.12 PowerNV
>>> [    0.000000] [      T0] printk: legacy bootconsole [udbg0] enabled
>>> [    0.000000] [      T0] CPU maps initialized for 8 threads per core
>>> [    0.000000] [      T0]  (thread shift is 3)
>>>>> But I my opal version 5.4.12.
>>>
>>> Thanks for reporting the issue, will have an look at it.
>>
>> I bisected it to a change between 5.19-rc3 and 5.19-rc4, and merge 
>> commit 8100775d59a6 (Merge tag 'powerpc-5.19-3' of git:// 
>> git.kernel.org/ pub/scm/linux/kernel/git/powerpc/linux) [1] indeed has 
>> rng related changes
>>
>>>  - Three fixes to wire up our various RNGs earlier in boot so they're
>>>    available for use in the initial seeding in random_init().
> 
> I confirmed, that commit f3eac426657d (powerpc/powernv: wire up rng 
> during setup_arch) [2] introduced the Oops.
> 
>>> [    0.000000] [      T0] Allocated 4608 bytes for 160 pacas
>>> [    0.000000] [      T0] 
>>> -----------------------------------------------------
>>>
>>> .......
>>>
>>> [   37.407674] [    T900] audit: type=1130 audit(1778043621.931:10): pid=1 uid=0 auid=4294967295 ses=4294967295 msg='unit=lvm2-monitor comm="systemd" exe="/usr/lib/systemd/systemd" hostname=? addr=? terminal=? res=success'
>>> [   37.413015] [    T900] audit: type=1130 audit(1778043621.937:11): pid=1 uid=0 auid=4294967295 ses=4294967295 msg='unit=systemd-sysctl comm="systemd" exe="/usr/lib/systemd/systemd" hostname=? addr=? terminal=? res=success'
>>> [   38.448156] [   T2286] powernv_rng: Registered powernv hwrng.
>>> [   38.575227] [   T2264] tg3 0005:09:00.1 enP5p9s0f1: renamed from eth1
>>> [   38.582176] [   T2223] tg3 0005:09:00.2 enP5p9s0f2: renamed from eth2
>>> ........
>>>
>>> ////cpuinfo output
>>>
>>> processor    : 159
>>>
>>> cpu        : POWER8E (raw), altivec supported
>>> clock        : 2061.000000MHz
>>> revision    : 2.1 (pvr 004b 0201)
>>>
>>> timebase    : 512000000
>>> platform    : PowerNV
>>> model        : 8247-22L
>>> machine        : PowerNV 8247-22L
>>> firmware    : OPAL
>>> MMU        : Hash
>>>
>>>
>>> But my system opal version 5.4.12.
>>> Thanks for reporting the issue, will have an look at it.

Were you able to take a look? I sent in a patch [3], that hasn’t gotten 
any response.


Kind regards,

Paul


>> [1]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=8100775d59a6789c3c6c309de26fac52f129cba8
> [2]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=f3eac426657d985b97c92fa5f7ae1d43f04721f3
[3]: 
https://lore.kernel.org/all/20260511120413.254934-2-pmenzel@molgen.mpg.de/