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Date: Tue, 26 Oct 2021 10:48:23 +0200
From: John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>
To: mpe@...erman.id.au
Cc: linuxppc-dev@...ts.ozlabs.org, oss-security@...ts.openwall.com,
"debian-powerpc@...ts.debian.org" <debian-powerpc@...ts.debian.org>
Subject: Re: Linux kernel: powerpc: KVM guest can trigger host crash on Power8
Hi Michael!
> The Linux kernel for powerpc since v5.2 has a bug which allows a
> malicious KVM guest to crash the host, when the host is running on
> Power8.
>
> Only machines using Linux as the hypervisor, aka. KVM, powernv or bare
> metal, are affected by the bug. Machines running PowerVM are not
> affected.
>
> The bug was introduced in:
>
> 10d91611f426 ("powerpc/64s: Reimplement book3s idle code in C")
>
> Which was first released in v5.2.
>
> The upstream fix is:
>
> cdeb5d7d890e ("KVM: PPC: Book3S HV: Make idle_kvm_start_guest() return 0 if it went to guest")
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=cdeb5d7d890e14f3b70e8087e745c4a6a7d9f337
>
> Which will be included in the v5.16 release.
I have tested these patches against 5.14 but it seems the problem [1] still remains for me
for big-endian guests. I built a patched kernel yesterday, rebooted the KVM server and let
the build daemons do their work over night.
When I got up this morning, I noticed the machine was down, so I checked the serial console
via IPMI and saw the same messages again as reported in [1]:
[41483.963562] watchdog: BUG: soft lockup - CPU#104 stuck for 25521s! [migration/104:175]
[41507.963307] watchdog: BUG: soft lockup - CPU#104 stuck for 25544s! [migration/104:175]
[41518.311200] rcu: INFO: rcu_sched detected stalls on CPUs/tasks:
[41518.311216] rcu: 136-...0: (135 ticks this GP) idle=242/1/0x4000000000000000 softirq=32031/32033 fqs=2729959
[41547.962882] watchdog: BUG: soft lockup - CPU#104 stuck for 25581s! [migration/104:175]
[41571.962627] watchdog: BUG: soft lockup - CPU#104 stuck for 25603s! [migration/104:175]
[41581.330530] rcu: INFO: rcu_sched detected stalls on CPUs/tasks:
[41581.330546] rcu: 136-...0: (135 ticks this GP) idle=242/1/0x4000000000000000 softirq=32031/32033 fqs=2736378
[41611.962202] watchdog: BUG: soft lockup - CPU#104 stuck for 25641s! [migration/104:175]
[41635.961947] watchdog: BUG: soft lockup - CPU#104 stuck for 25663s! [migration/104:175]
[41644.349859] rcu: INFO: rcu_sched detected stalls on CPUs/tasks:
[41644.349876] rcu: 136-...0: (135 ticks this GP) idle=242/1/0x4000000000000000 softirq=32031/32033 fqs=2742753
[41671.961564] watchdog: BUG: soft lockup - CPU#104 stuck for 25697s! [migration/104:175]
[41695.961309] watchdog: BUG: soft lockup - CPU#104 stuck for 25719s! [migration/104:175]
[41707.369190] rcu: INFO: rcu_sched detected stalls on CPUs/tasks:
[41707.369206] rcu: 136-...0: (135 ticks this GP) idle=242/1/0x4000000000000000 softirq=32031/32033 fqs=2749151
[41735.960884] watchdog: BUG: soft lockup - CPU#104 stuck for 25756s! [migration/104:175]
[41759.960629] watchdog: BUG: soft lockup - CPU#104 stuck for 25778s! [migration/104:175]
[41770.388520] rcu: INFO: rcu_sched detected stalls on CPUs/tasks:
[41770.388548] rcu: 136-...0: (135 ticks this GP) idle=242/1/0x4000000000000000 softirq=32031/32033 fqs=2755540
[41776.076307] rcu: rcu_sched kthread timer wakeup didn't happen for 1423 jiffies! g49897 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402
[41776.076327] rcu: Possible timer handling issue on cpu=32 timer-softirq=1056014
[41776.076336] rcu: rcu_sched kthread starved for 1424 jiffies! g49897 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402 ->cpu=32
[41776.076350] rcu: Unless rcu_sched kthread gets sufficient CPU time, OOM is now expected behavior.
[41776.076360] rcu: RCU grace-period kthread stack dump:
[41776.076434] rcu: Stack dump where RCU GP kthread last ran:
[41783.960374] watchdog: BUG: soft lockup - CPU#104 stuck for 25801s! [migration/104:175]
[41807.960119] watchdog: BUG: soft lockup - CPU#104 stuck for 25823s! [migration/104:175]
[41831.959864] watchdog: BUG: soft lockup - CPU#104 stuck for 25846s! [migration/104:175]
[41833.407851] rcu: INFO: rcu_sched detected stalls on CPUs/tasks:
[41833.407868] rcu: 136-...0: (135 ticks this GP) idle=242/1/0x4000000000000000 softirq=32031/32033 fqs=2760381
[41863.959524] watchdog: BUG: soft lockup - CPU#104 stuck for 25875s! [migration/104:175]
It seems that in this case, it was the testsuite of the git package [2] that triggered the bug. As you
can see from the overview, the git package has been in the building state for 8 hours meaning the
build server crashed and is no longer giving feedback to the database.
Adrian
> [1] https://bugzilla.kernel.org/show_bug.cgi?id=206669
> [2] https://buildd.debian.org/status/package.php?p=git&suite=experimental
--
.''`. John Paul Adrian Glaubitz
: :' : Debian Developer - glaubitz@...ian.org
`. `' Freie Universitaet Berlin - glaubitz@...sik.fu-berlin.de
`- GPG: 62FF 8A75 84E0 2956 9546 0006 7426 3B37 F5B5 F913
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