// For flags

CVE-2021-47227

x86/fpu: Prevent state corruption in __fpu__restore_sig()

Severity Score

"-"
*CVSS v-

Exploit Likelihood

*EPSS

Affected Versions

*CPE

Public Exploits

0
*Multiple Sources

Exploited in Wild

-
*KEV

Decision

Track
*SSVC
Descriptions

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

x86/fpu: Prevent state corruption in __fpu__restore_sig()

The non-compacted slowpath uses __copy_from_user() and copies the entire
user buffer into the kernel buffer, verbatim. This means that the kernel
buffer may now contain entirely invalid state on which XRSTOR will #GP.
validate_user_xstate_header() can detect some of that corruption, but that
leaves the onus on callers to clear the buffer.

Prior to XSAVES support, it was possible just to reinitialize the buffer,
completely, but with supervisor states that is not longer possible as the
buffer clearing code split got it backwards. Fixing that is possible but
not corrupting the state in the first place is more robust.

Avoid corruption of the kernel XSAVE buffer by using copy_user_to_xstate()
which validates the XSAVE header contents before copying the actual states
to the kernel. copy_user_to_xstate() was previously only called for
compacted-format kernel buffers, but it works for both compacted and
non-compacted forms.

Using it for the non-compacted form is slower because of multiple
__copy_from_user() operations, but that cost is less important than robust
code in an already slow path.

[ Changelog polished by Dave Hansen ]

En el kernel de Linux, se resolvió la siguiente vulnerabilidad: x86/fpu: evita la corrupción del estado en __fpu__restore_sig() La ruta lenta no compactada usa __copy_from_user() y copia todo el búfer del usuario en el búfer del kernel, palabra por palabra. Esto significa que el búfer del kernel ahora puede contener un estado completamente inválido en el que XRSTOR realizará #GP. validar_user_xstate_header() puede detectar parte de esa corrupción, pero eso deja a las personas que llaman la responsabilidad de borrar el búfer. Antes de la compatibilidad con XSAVES, era posible simplemente reinicializar el búfer por completo, pero con los estados del supervisor eso ya no es posible porque la división del código de borrado del búfer lo hacía al revés. Arreglar eso es posible, pero no corromper al Estado en primer lugar es más sólido. Evite la corrupción del búfer XSAVE del kernel utilizando copy_user_to_xstate() que valida el contenido del encabezado XSAVE antes de copiar los estados reales al kernel. copy_user_to_xstate() anteriormente solo se llamaba para buffers del kernel en formato compacto, pero funciona tanto para formatos compactos como no compactos. Usarlo para el formato no compacto es más lento debido a múltiples operaciones __copy_from_user(), pero ese costo es menos importante que el código robusto en una ruta que ya es lenta. [Registro de cambios pulido por Dave Hansen]

*Credits: N/A
CVSS Scores
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Scope
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Confidentiality
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Integrity
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Availability
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* Common Vulnerability Scoring System
SSVC
  • Decision:Track
Exploitation
None
Automatable
No
Tech. Impact
Partial
* Organization's Worst-case Scenario
Timeline
  • 2024-04-10 CVE Reserved
  • 2024-05-21 CVE Published
  • 2024-05-22 EPSS Updated
  • 2024-12-19 CVE Updated
  • ---------- Exploited in Wild
  • ---------- KEV Due Date
  • ---------- First Exploit
CWE
CAPEC
Affected Vendors, Products, and Versions
Vendor Product Version Other Status
Vendor Product Version Other Status <-- --> Vendor Product Version Other Status
Linux
Search vendor "Linux"
Linux Kernel
Search vendor "Linux" for product "Linux Kernel"
>= 5.8 < 5.10.46
Search vendor "Linux" for product "Linux Kernel" and version " >= 5.8 < 5.10.46"
en
Affected
Linux
Search vendor "Linux"
Linux Kernel
Search vendor "Linux" for product "Linux Kernel"
>= 5.8 < 5.12.13
Search vendor "Linux" for product "Linux Kernel" and version " >= 5.8 < 5.12.13"
en
Affected
Linux
Search vendor "Linux"
Linux Kernel
Search vendor "Linux" for product "Linux Kernel"
>= 5.8 < 5.13
Search vendor "Linux" for product "Linux Kernel" and version " >= 5.8 < 5.13"
en
Affected