GSD-2021-46990
Vulnerability from gsd - Updated: 2024-02-28 06:03Details
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.
Aliases
{
"gsd": {
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"remediation": "unknown",
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"details": "In the Linux kernel, the following vulnerability has been resolved:\n\npowerpc/64s: Fix crashes when toggling entry flush barrier\n\nThe entry flush mitigation can be enabled/disabled at runtime via a\ndebugfs file (entry_flush), which causes the kernel to patch itself to\nenable/disable the relevant mitigations.\n\nHowever depending on which mitigation we\u0027re using, it may not be safe to\ndo that patching while other CPUs are active. For example the following\ncrash:\n\n sleeper[15639]: segfault (11) at c000000000004c20 nip c000000000004c20 lr c000000000004c20\n\nShows that we returned to userspace with a corrupted LR that points into\nthe kernel, due to executing the partially patched call to the fallback\nentry flush (ie. we missed the LR restore).\n\nFix it by doing the patching under stop machine. The CPUs that aren\u0027t\ndoing the patching will be spinning in the core of the stop machine\nlogic. That is currently sufficient for our purposes, because none of\nthe patching we do is to that code or anywhere in the vicinity.",
"id": "GSD-2021-46990",
"modified": "2024-02-28T06:03:57.796491Z",
"schema_version": "1.4.0"
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}
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"id": "CVE-2021-46990",
"lastModified": "2024-02-28T14:06:45.783",
"metrics": {},
"published": "2024-02-28T09:15:37.733",
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Sightings
| Author | Source | Type | Date |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
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