CVE-2021-47553

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Source
https://nvd.nist.gov/vuln/detail/CVE-2021-47553
Import Source
https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2021-47553.json
JSON Data
https://api.osv.dev/v1/vulns/CVE-2021-47553
Related
Published
2024-05-24T15:15:20Z
Modified
2024-09-18T03:18:53.134118Z
Summary
[none]
Details

In the Linux kernel, the following vulnerability has been resolved:

sched/scs: Reset task stack state in bringup_cpu()

To hot unplug a CPU, the idle task on that CPU calls a few layers of C code before finally leaving the kernel. When KASAN is in use, poisoned shadow is left around for each of the active stack frames, and when shadow call stacks are in use. When shadow call stacks (SCS) are in use the task's saved SCS SP is left pointing at an arbitrary point within the task's shadow call stack.

When a CPU is offlined than onlined back into the kernel, this stale state can adversely affect execution. Stale KASAN shadow can alias new stackframes and result in bogus KASAN warnings. A stale SCS SP is effectively a memory leak, and prevents a portion of the shadow call stack being used. Across a number of hotplug cycles the idle task's entire shadow call stack can become unusable.

We previously fixed the KASAN issue in commit:

e1b77c92981a5222 ("sched/kasan: remove stale KASAN poison after hotplug")

... by removing any stale KASAN stack poison immediately prior to onlining a CPU.

Subsequently in commit:

f1a0a376ca0c4ef1 ("sched/core: Initialize the idle task with preemption disabled")

... the refactoring left the KASAN and SCS cleanup in one-time idle thread initialization code rather than something invoked prior to each CPU being onlined, breaking both as above.

We fixed SCS (but not KASAN) in commit:

63acd42c0d4942f7 ("sched/scs: Reset the shadow stack when idletaskexit")

... but as this runs in the context of the idle task being offlined it's potentially fragile.

To fix these consistently and more robustly, reset the SCS SP and KASAN shadow of a CPU's idle task immediately before we online that CPU in bringup_cpu(). This ensures the idle task always has a consistent state when it is running, and removes the need to so so when exiting an idle task.

Whenever any thread is created, duptaskstruct() will give the task a stack which is free of KASAN shadow, and initialize the task's SCS SP, so there's no need to specially initialize either for idle thread within init_idle(), as this was only necessary to handle hotplug cycles.

I've tested this on arm64 with:

  • gcc 11.1.0, defconfig +KASANINLINE, KASANSTACK
  • clang 12.0.0, defconfig +KASANINLINE, KASANSTACK, SHADOWCALLSTACK

... offlining and onlining CPUS with:

| while true; do | for C in /sys/devices/system/cpu/cpu*/online; do | echo 0 > $C; | echo 1 > $C; | done | done

References

Affected packages

Debian:11 / linux

Package

Name
linux
Purl
pkg:deb/debian/linux?arch=source

Affected ranges

Type
ECOSYSTEM
Events
Introduced
0Unknown introduced version / All previous versions are affected
Fixed
5.10.84-1

Affected versions

5.*

5.10.46-4
5.10.46-5
5.10.70-1~bpo10+1
5.10.70-1

Ecosystem specific

{
    "urgency": "not yet assigned"
}

Debian:12 / linux

Package

Name
linux
Purl
pkg:deb/debian/linux?arch=source

Affected ranges

Type
ECOSYSTEM
Events
Introduced
0Unknown introduced version / All previous versions are affected
Fixed
5.15.15-1

Ecosystem specific

{
    "urgency": "not yet assigned"
}

Debian:13 / linux

Package

Name
linux
Purl
pkg:deb/debian/linux?arch=source

Affected ranges

Type
ECOSYSTEM
Events
Introduced
0Unknown introduced version / All previous versions are affected
Fixed
5.15.15-1

Ecosystem specific

{
    "urgency": "not yet assigned"
}