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Message-ID: <4a5c8d28-7f73-4c15-b288-641f0ccc91c2@redhat.com>
Date: Mon, 11 Mar 2024 10:31:41 +0100
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Subject: Re: BUG selftests/mm]
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To: Mirsad Todorovac <mirsad.todorovac@alu.unizg.hr>, linux-mm@kvack.org
Cc: Peter Xu <peterx@redhat.com>, Andrew Morton <akpm@linux-foundation.org>,
 Shuah Khan <shuah@kernel.org>, linux-kselftest@vger.kernel.org,
 linux-kernel@vger.kernel.org, Axel Rasmussen <axelrasmussen@google.com>
References: <a9e3120d-8b79-4435-b113-ceb20aa45ee2@alu.unizg.hr>
From: David Hildenbrand <david@redhat.com>
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In-Reply-To: <a9e3120d-8b79-4435-b113-ceb20aa45ee2@alu.unizg.hr>
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On 09.03.24 20:12, Mirsad Todorovac wrote:
> Hi,
> 
> Routine run of the test in net-next gave also this mm unit error.
> 
> root@defiant:tools/testing/selftests/mm# ./uffd-unit-tests
> Testing UFFDIO_API (with syscall)... done
> Testing UFFDIO_API (with /dev/userfaultfd)... done
> Testing register-ioctls on anon... done
> Testing register-ioctls on shmem... done
> Testing register-ioctls on shmem-private... done
> Testing register-ioctls on hugetlb... skipped [reason: memory allocation failed]
> Testing register-ioctls on hugetlb-private... skipped [reason: memory allocation failed]
> Testing zeropage on anon... done
> Testing zeropage on shmem... done
> Testing zeropage on shmem-private... done
> Testing zeropage on hugetlb... skipped [reason: memory allocation failed]
> Testing zeropage on hugetlb-private... skipped [reason: memory allocation failed]
> Testing move on anon... done
> Testing move-pmd on anon... done
> Testing move-pmd-split on anon... done
> Testing wp-fork on anon... done
> Testing wp-fork on shmem... done
> Testing wp-fork on shmem-private... done
> Testing wp-fork on hugetlb... skipped [reason: memory allocation failed]
> Testing wp-fork on hugetlb-private... skipped [reason: memory allocation failed]
> Testing wp-fork-with-event on anon... done
> Testing wp-fork-with-event on shmem... done
> Testing wp-fork-with-event on shmem-private... done
> Testing wp-fork-with-event on hugetlb... skipped [reason: memory allocation failed]
> Testing wp-fork-with-event on hugetlb-private... skipped [reason: memory allocation failed]
> Testing wp-fork-pin on anon... done
> Testing wp-fork-pin on shmem... done
> Testing wp-fork-pin on shmem-private... done
> Testing wp-fork-pin on hugetlb... skipped [reason: memory allocation failed]
> Testing wp-fork-pin on hugetlb-private... skipped [reason: memory allocation failed]
> Testing wp-fork-pin-with-event on anon... done
> Testing wp-fork-pin-with-event on shmem... done
> Testing wp-fork-pin-with-event on shmem-private... done
> Testing wp-fork-pin-with-event on hugetlb... skipped [reason: memory allocation failed]
> Testing wp-fork-pin-with-event on hugetlb-private... skipped [reason: memory allocation failed]
> Testing wp-unpopulated on anon... done
> Testing minor on shmem... done
> Testing minor on hugetlb... skipped [reason: memory allocation failed]
> Testing minor-wp on shmem... done
> Testing minor-wp on hugetlb... skipped [reason: memory allocation failed]
> Testing minor-collapse on shmem... done
> Testing sigbus on anon... done
> Testing sigbus on shmem... done
> Testing sigbus on shmem-private... done
> Testing sigbus on hugetlb... skipped [reason: memory allocation failed]
> Testing sigbus on hugetlb-private... skipped [reason: memory allocation failed]
> Testing sigbus-wp on anon... done
> Testing sigbus-wp on shmem... done
> Testing sigbus-wp on shmem-private... done
> Testing sigbus-wp on hugetlb... skipped [reason: memory allocation failed]
> Testing sigbus-wp on hugetlb-private... skipped [reason: memory allocation failed]
> Testing events on anon... done
> Testing events on shmem... done
> Testing events on shmem-private... done
> Testing events on hugetlb... skipped [reason: memory allocation failed]
> Testing events on hugetlb-private... skipped [reason: memory allocation failed]
> Testing events-wp on anon... done
> Testing events-wp on shmem... done
> Testing events-wp on shmem-private... done
> Testing events-wp on hugetlb... skipped [reason: memory allocation failed]
> Testing events-wp on hugetlb-private... skipped [reason: memory allocation failed]
> Testing poison on anon... done
> Testing poison on shmem... done
> Testing poison on shmem-private... done
> Testing poison on hugetlb... skipped [reason: memory allocation failed]
> Testing poison on hugetlb-private... skipped [reason: memory allocation failed]
> Userfaults unit tests: pass=42, skip=24, fail=0 (total=66)
> root@defiant:tools/testing/selftests/mm# grep -i huge /proc/meminfo
> 
> It resulted in alarming errors in the syslog:
> 
> Mar  9 19:48:24 defiant kernel: [77187.055103] MCE: Killing uffd-unit-tests:1321817 due to hardware memory corruption fault at 4631e000
> Mar  9 19:48:24 defiant kernel: [77187.055132] MCE: Killing uffd-unit-tests:1321817 due to hardware memory corruption fault at 46320000
> Mar  9 19:48:24 defiant kernel: [77187.055160] MCE: Killing uffd-unit-tests:1321817 due to hardware memory corruption fault at 46322000
> Mar  9 19:48:24 defiant kernel: [77187.055189] MCE: Killing uffd-unit-tests:1321817 due to hardware memory corruption fault at 46324000
> Mar  9 19:48:24 defiant kernel: [77187.055218] MCE: Killing uffd-unit-tests:1321817 due to hardware memory corruption fault at 46326000
> Mar  9 19:48:24 defiant kernel: [77187.055250] MCE: Killing uffd-unit-tests:1321817 due to hardware memory corruption fault at 46328000
> Mar  9 19:48:24 defiant kernel: [77187.055278] MCE: Killing uffd-unit-tests:1321817 due to hardware memory corruption fault at 4632a000
> Mar  9 19:48:24 defiant kernel: [77187.055307] MCE: Killing uffd-unit-tests:1321817 due to hardware memory corruption fault at 4632c000
> Mar  9 19:48:24 defiant kernel: [77187.055336] MCE: Killing uffd-unit-tests:1321817 due to hardware memory corruption fault at 4632e000
> Mar  9 19:48:24 defiant kernel: [77187.055366] MCE: Killing uffd-unit-tests:1321817 due to hardware memory corruption fault at 46330000
> Mar  9 19:48:24 defiant kernel: [77187.055395] MCE: Killing uffd-unit-tests:1321817 due to hardware memory corruption fault at 46332000
> Mar  9 19:48:24 defiant kernel: [77187.055423] MCE: Killing uffd-unit-tests:1321817 due to hardware memory corruption fault at 46334000
> Mar  9 19:48:24 defiant kernel: [77187.055452] MCE: Killing uffd-unit-tests:1321817 due to hardware memory corruption fault at 46336000
> Mar  9 19:48:24 defiant kernel: [77187.055480] MCE: Killing uffd-unit-tests:1321817 due to hardware memory corruption fault at 46338000
> Mar  9 19:48:24 defiant kernel: [77187.055509] MCE: Killing uffd-unit-tests:1321817 due to hardware memory corruption fault at 4633a000
> Mar  9 19:48:24 defiant kernel: [77187.055538] MCE: Killing uffd-unit-tests:1321817 due to hardware memory corruption fault at 4633c000
> Mar  9 19:48:24 defiant kernel: [77187.055567] MCE: Killing uffd-unit-tests:1321817 due to hardware memory corruption fault at 4633e000
> Mar  9 19:48:24 defiant kernel: [77187.055597] MCE: Killing uffd-unit-tests:1321817 due to hardware memory corruption fault at 46340000
> 
> At this point, it can be problem with my box's memory chips, or something with HUGETLB.
> 
> However, since the "classic" allocations were successful, the problem might be in huge pages, or
> if I understood well, in deliberate poisoning of pages?
> 

Isn't that just the (expected) side effect of UFFDIO_POISON tests?

IOW, there is no problem here. We are poisoning virtual memory locations 
(not actual memory) and expect a SIGBUS on next access. While testing 
that, we receive these messages.

The "ugly" thing here seems to be that we can trigger repeated pr_err() 
from user space. There is no rate-limiting in place. Maybe UFFDIO_POISON 
requires root permissions so this cannot be exploited by unprivileged 
user space to flood the system log?

CCing Axel

-- 
Cheers,

David / dhildenb