Linux kernel: powerpc: KVM guest can trigger host crash on Power8

[Michael Ellerman]

[ Dropping oss-security from Cc]

John Paul Adrian Glaubitz <glaubitz at physik.fu-berlin.de> writes:
> On 10/27/21 13:06, Michael Ellerman wrote:
>> John Paul Adrian Glaubitz <glaubitz at physik.fu-berlin.de> writes:
>>> On 10/27/21 07:30, Michael Ellerman wrote:
>>>> I did test the repro case you gave me before (in the bugzilla), which
>>>> was building glibc, that passes for me with a patched host.
>>>
>>> Did you manage to crash the unpatched host?
>> 
>> Yes, the parallel builds of glibc you described crashed the unpatched
>> host 100% reliably for me.
>
> OK, that is very good news!
>
>> I also have a standalone reproducer I'll send you.
>
> Thanks, that would be helpful!
>
>>> Also, I'll try a kernel from git with Debian's config.
>>>
>>>> I guess we have yet another bug.
>>>>
>>>> I tried the following in a debian BE VM and it completed fine:
>>>>
>>>>  $ dget -u http://ftp.debian.org/debian/pool/main/g/git/git_2.33.1-1.dsc
>>>>  $ sbuild -d sid --arch=powerpc --no-arch-all git_2.33.1-1.dsc
>>>>
>>>> Same for ppc64.
>>>>
>>>> And I also tried both at once, repeatedly in a loop.
>>>
>>> Did you try building gcc-11 for powerpc and ppc64 both at once?
>> 
>> No, I will try that now.

That completed fine on my BE VM here.

I ran these in two tmux windows:
  $ sbuild -d sid --arch=powerpc --no-arch-all gcc-11_11.2.0-10.dsc
  $ sbuild -d sid --arch=ppc64 --no-arch-all gcc-11_11.2.0-10.dsc


The VM has 32 CPUs, with 4 threads per core:

  $ ppc64_cpu --info
  Core   0:    0*    1*    2*    3*
  Core   1:    4*    5*    6*    7*
  Core   2:    8*    9*   10*   11*
  Core   3:   12*   13*   14*   15*
  Core   4:   16*   17*   18*   19*
  Core   5:   20*   21*   22*   23*
  Core   6:   24*   25*   26*   27*
  Core   7:   28*   29*   30*   31*


cheers