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Date:   Thu, 16 Apr 2020 22:17:53 -0400
From:   Steven Rostedt <rostedt@goodmis.org>
To:     Qian Cai <cai@lca.pw>
Cc:     Michael Ellerman <mpe@ellerman.id.au>,
        Russell Currey <ruscur@russell.cc>,
        Nicholas Piggin <npiggin@gmail.com>,
        linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: POWER9 crash due to STRICT_KERNEL_RWX (WAS: Re: Linux-next
 POWER9 NULL pointer NIP...)
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On Thu, 16 Apr 2020 21:19:10 -0400
Qian Cai <cai@lca.pw> wrote:

> OK, reverted the commit,
> 
> c55d7b5e6426 (“powerpc: Remove STRICT_KERNEL_RWX incompatibility with RELOCATABLE”)
> 
> or set STRICT_KERNEL_RWX=n fixed the crash below and also mentioned in this thread,

This may be a symptom and not a cure.

> 
> 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=64K MMU=Radix SMP NR_CPUS=256 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 
> [  148.255310][T13380] GPR00: c000000000973268 c0000010a6fafc90 c000000001648200 0000000000000000 
> [  148.255310][T13380] GPR04: c000000d8a22dc00 c0000010a6fafd30 00000000b5e98331 ffffffff00012c9f 
> [  148.255310][T13380] GPR08: c000000d8a22dc00 0000000000000000 0000000000000000 c00000000163c520 
> [  148.255310][T13380] GPR12: c0000000016804ac c000001ffffdad80 0000000000000000 0000000000000000 
> [  148.255310][T13380] GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 
> [  148.255310][T13380] GPR20: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 
> [  148.255310][T13380] GPR24: 00007fff8f5e2e48 0000000000000000 c00800000fa6a488 c0000010a6fafd30 
> [  148.255310][T13380] GPR28: 0000000000000000 000000007fffffff c00800000fa60400 c000000efd0c6780 
> [  148.255494][T13380] NIP [c0000000016804ac] sysctl_net_busy_read+0x0/0x4

The instruction pointer is on sysctl_net_busy_read? Isn't that data and
not code?

In net/socket.c:

  #ifdef CONFIG_NET_RX_BUSY_POLL
  unsigned int sysctl_net_busy_read __read_mostly;
  unsigned int sysctl_net_busy_poll __read_mostly;
  #endif

-- Steve


> [  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 
> [  148.255744][T13380] XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX 
> [  148.255772][T13380] ---[ end trace a5894a74208c22ec ]---
> [  148.576663][T13380] 
> [  149.576765][T13380] Kernel panic - not syncing: Fatal exception
>