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Subject: POWER9 crash due to STRICT_KERNEL_RWX (WAS: Re: Linux-next POWER9
 NULL pointer NIP...)
From:   Qian Cai <cai@lca.pw>
In-Reply-To: <161662E3-5D9C-4C15-919C-CFEFE4CC35CB@lca.pw>
Date:   Thu, 16 Apr 2020 21:19:10 -0400
Cc:     Nicholas Piggin <npiggin@gmail.com>,
        linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>
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References: <15AC5B0E-A221-4B8C-9039-FA96B8EF7C88@lca.pw>
 <87eeszlb6u.fsf@mpe.ellerman.id.au>
 <0675B22E-8F32-432C-9378-FDE159DD1729@lca.pw>
 <20200407093054.3eb23e45@gandalf.local.home>
 <EA9F9A54-87BC-477A-BE8A-7D53F80C5223@lca.pw>
 <20200409101413.35d9c72d@gandalf.local.home>
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 <161662E3-5D9C-4C15-919C-CFEFE4CC35CB@lca.pw>
To:     Michael Ellerman <mpe@ellerman.id.au>,
        Russell Currey <ruscur@russell.cc>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

OK, reverted the commit,

c55d7b5e6426 (=E2=80=9Cpowerpc: Remove STRICT_KERNEL_RWX incompatibility =
with RELOCATABLE=E2=80=9D)

or set STRICT_KERNEL_RWX=3Dn fixed the crash below and also mentioned in =
this thread,

=
https://lore.kernel.org/lkml/15AC5B0E-A221-4B8C-9039-FA96B8EF7C88@lca.pw/

[  148.110969][T13115] LTP: starting chown04_16
[  148.255048][T13380] kernel tried to execute exec-protected page =
(c0000000016804ac) - exploit attempt? (uid: 0)
[  148.255099][T13380] BUG: Unable to handle kernel instruction fetch
[  148.255122][T13380] Faulting instruction address: 0xc0000000016804ac
[  148.255136][T13380] Oops: Kernel access of bad area, sig: 11 [#1]
[  148.255157][T13380] LE PAGE_SIZE=3D64K MMU=3DRadix SMP NR_CPUS=3D256 =
DEBUG_PAGEALLOC NUMA PowerNV
[  148.255171][T13380] Modules linked in: loop kvm_hv kvm xfs sd_mod =
bnx2x mdio ahci tg3 libahci libphy libata firmware_class dm_mirror =
dm_region_hash dm_log dm_mod
[  148.255213][T13380] CPU: 45 PID: 13380 Comm: chown04_16 Tainted: G    =
    W         5.6.0+ #7
[  148.255236][T13380] NIP:  c0000000016804ac LR: c00800000fa60408 CTR: =
c0000000016804ac
[  148.255250][T13380] REGS: c0000010a6fafa00 TRAP: 0400   Tainted: G    =
    W          (5.6.0+)
[  148.255281][T13380] MSR:  9000000010009033 <SF,HV,EE,ME,IR,DR,RI,LE>  =
CR: 84000248  XER: 20040000
[  148.255310][T13380] CFAR: c00800000fa66534 IRQMASK: 0=20
[  148.255310][T13380] GPR00: c000000000973268 c0000010a6fafc90 =
c000000001648200 0000000000000000=20
[  148.255310][T13380] GPR04: c000000d8a22dc00 c0000010a6fafd30 =
00000000b5e98331 ffffffff00012c9f=20
[  148.255310][T13380] GPR08: c000000d8a22dc00 0000000000000000 =
0000000000000000 c00000000163c520=20
[  148.255310][T13380] GPR12: c0000000016804ac c000001ffffdad80 =
0000000000000000 0000000000000000=20
[  148.255310][T13380] GPR16: 0000000000000000 0000000000000000 =
0000000000000000 0000000000000000=20
[  148.255310][T13380] GPR20: 0000000000000000 0000000000000000 =
0000000000000000 0000000000000000=20
[  148.255310][T13380] GPR24: 00007fff8f5e2e48 0000000000000000 =
c00800000fa6a488 c0000010a6fafd30=20
[  148.255310][T13380] GPR28: 0000000000000000 000000007fffffff =
c00800000fa60400 c000000efd0c6780=20
[  148.255494][T13380] NIP [c0000000016804ac] =
sysctl_net_busy_read+0x0/0x4
[  148.255516][T13380] LR [c00800000fa60408] find_free_cb+0x8/0x30 =
[loop]
[  148.255528][T13380] Call Trace:
[  148.255538][T13380] [c0000010a6fafc90] [c0000000009732c0] =
idr_for_each+0xf0/0x170 (unreliable)
[  148.255572][T13380] [c0000010a6fafd10] [c00800000fa626c4] =
loop_lookup.part.1+0x4c/0xb0 [loop]
[  148.255597][T13380] [c0000010a6fafd50] [c00800000fa634d8] =
loop_control_ioctl+0x120/0x1d0 [loop]
[  148.255623][T13380] [c0000010a6fafdb0] [c0000000004ddc08] =
ksys_ioctl+0xd8/0x130
[  148.255636][T13380] [c0000010a6fafe00] [c0000000004ddc88] =
sys_ioctl+0x28/0x40
[  148.255669][T13380] [c0000010a6fafe20] [c00000000000b378] =
system_call+0x5c/0x68
[  148.255699][T13380] Instruction dump:
[  148.255718][T13380] XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX =
XXXXXXXX XXXXXXXX XXXXXXXX=20
[  148.255744][T13380] XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX =
XXXXXXXX XXXXXXXX XXXXXXXX=20
[  148.255772][T13380] ---[ end trace a5894a74208c22ec ]---
[  148.576663][T13380]=20
[  149.576765][T13380] Kernel panic - not syncing: Fatal exception