UBUNTU-CVE-2021-46990
In the Linux kernel, the following vulnerability has been resolved: powerpc/64s: Fix crashes when toggling entry flush barrier The entry flush mitigation can be enabled/disabled at runtime via a debugfs file (entry_flush), which causes the kernel to patch itself to enable/disable the relevant mitigations. However depending on which mitigation we're using, it may not be safe to do that patching while other CPUs are active. For example the following crash: sleeper[15639]: segfault (11) at c000000000004c20 nip c000000000004c20 lr c000000000004c20 Shows that we returned to userspace with a corrupted LR that points into the kernel, due to executing the partially patched call to the fallback entry flush (ie. we missed the LR restore). Fix it by doing the patching under stop machine. The CPUs that aren't doing the patching will be spinning in the core of the stop machine logic. That is currently sufficient for our purposes, because none of the patching we do is to that code or anywhere in the vicinity.
02 / AFFECTED SOFTWARE
Affected packages
50 explicit affected versions
6 explicit affected versions
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2 explicit affected versions
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67 explicit affected versions
28 explicit affected versions
47 explicit affected versions
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35 explicit affected versions
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77 explicit affected versions
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95 explicit affected versions
1 explicit affected versions
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12 explicit affected versions
1 explicit affected versions
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12 explicit affected versions
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37 explicit affected versions
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10 explicit affected versions
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13 explicit affected versions
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13 explicit affected versions
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11 explicit affected versions
12 explicit affected versions
69 explicit affected versions
7 explicit affected versions
12 explicit affected versions
31 explicit affected versions
26 explicit affected versions
10 explicit affected versions
26 explicit affected versions
13 explicit affected versions
16 explicit affected versions
3 explicit affected versions
51 explicit affected versions
23 explicit affected versions
12 explicit affected versions
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1 explicit affected versions
26 explicit affected versions
8 explicit affected versions
5 explicit affected versions
20 explicit affected versions
8 explicit affected versions
21 explicit affected versions
10 explicit affected versions
13 explicit affected versions
7 explicit affected versions
23 explicit affected versions
10 explicit affected versions
12 explicit affected versions
19 explicit affected versions
44 explicit affected versions
16 explicit affected versions
3 explicit affected versions
13 explicit affected versions
26 explicit affected versions
37 explicit affected versions
38 explicit affected versions
9 explicit affected versions
11 explicit affected versions
138 explicit affected versions
21 explicit affected versions
7 explicit affected versions
71 explicit affected versions
4 explicit affected versions
77 explicit affected versions
54 explicit affected versions
4 explicit affected versions
45 explicit affected versions
20 explicit affected versions
43 explicit affected versions
118 explicit affected versions
92 explicit affected versions
10 explicit affected versions
8 explicit affected versions
14 explicit affected versions
23 explicit affected versions
4 explicit affected versions
10 explicit affected versions
1 explicit affected versions
1 explicit affected versions
03 / CONNECTIONS
Connected vulnerabilities
04 / EVIDENCE
Source records
In the Linux kernel, the following vulnerability has been resolved: powerpc/64s: Fix crashes when toggling entry flush barrier The entry flush mitigation can be enabled/disabled at runtime via a debugfs file (entry_flush), which causes the kernel to patch itself to enable/disable the relevant mitigations. However depending on which mitigation we're using, it may not be safe to do that patching while other CPUs are active. For example the following crash: sleeper[15639]: segfault (11) at c000000000004c20 nip c000000000004c20 lr c000000000004c20 Shows that we returned to userspace with a corrupted LR that points into the kernel, due to executing the partially patched call to the fallback entry flush (ie. we missed the LR restore). Fix it by doing the patching under stop machine. The CPUs that aren't doing the patching will be spinning in the core of the stop machine logic. That is currently sufficient for our purposes, because none of the patching we do is to that code or anywhere in the vicinity.
05 / REFERENCES
Further evidence
- https://git.kernel.org/linus/aec86b052df6541cc97c5fca44e5934cbea4963b
- https://git.kernel.org/stable/c/0b4eb172cc12dc102cd0ad013e53ee4463db9508
- https://git.kernel.org/stable/c/0c25a7bb697f2e6ee65b6d63782f675bf129511a
- https://git.kernel.org/stable/c/2db22ba4e0e103f00e0512e0ecce36ac78c644f8
- https://git.kernel.org/stable/c/5bc00fdda1e934c557351a9c751a205293e68cbf
- https://git.kernel.org/stable/c/8382b15864e5014261b4f36c2aa89723612ee058
- https://git.kernel.org/stable/c/aec86b052df6541cc97c5fca44e5934cbea4963b
- https://git.kernel.org/stable/c/d2e3590ca39ccfd8a5a46d8c7f095cb6c7b9ae92
- https://git.kernel.org/stable/c/dd0d6117052faace5440db20fc37175efe921c7d
- https://git.kernel.org/stable/c/ee4b7aab93c2631c3bb0753023c5dda592bb666b
- https://ubuntu.com/security/CVE-2021-46990
- https://ubuntu.com/security/notices/USN-6739-1
- https://www.cve.org/CVERecord?id=CVE-2021-46990