CVE-2026-89775

Summary

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

KVM: arm64: Handle negative S1 walk levels in VNCR TLB size evaluation

Computing the effects of a TLB invalidation involves looking at the size of the mapping cached by the TLB. For S1 mappings such as VNCR, this is deducted from the combination of the base granule size and the mapping level.

However, this implies that the S1 MMU is on. When the MMU is off, we indicate this with the level being set to a "creative" value of -127 (S1_MMU_DISABLED).

This ends-up being misinterpreted by pgshift_level_to_ttl() as it doesn't handle negative levels at all (the level is immediately cast to a u8 and only the bottom two bits considered), leading to an invalidation size of 0. Not helpful.

Tidy-up pgshift_level_to_ttl() to handle these negative levels, and ttl_to_size() to always return SZ_1G when no valid TTL is present. This allows the removal of open-coded checks for similar situations.

Note that the check for a negative value not explicitely checking for S1_MMU_DISABLED is deliberate, so that actual negative levels introduced with LVA2 and D128 can take the same path if we ever support them.

Affected Software

VendorProductVersion RangeStatus
LinuxLinux7270cc9157f474dfc46750a34c9d7defc686b2eb < be54a70067c7dbe1381157e8a238fa4b16ea9c05affected
LinuxLinux7270cc9157f474dfc46750a34c9d7defc686b2eb < 1c9fca34b9625a67a7f1a03c8604f3df760c6c49affected
LinuxLinux7270cc9157f474dfc46750a34c9d7defc686b2eb < 8053393680d4fa3eb962667d2be95dd39f0940e5affected
LinuxLinux6.16affected
LinuxLinux0 < 6.16unaffected
LinuxLinux6.18.51 <= 6.18.*unaffected
LinuxLinux7.2.5 <= 7.2.*unaffected
LinuxLinux7.3-rc1 <= *unaffected

Weaknesses

ADP Enrichment

CVE Program Container

Additional References

References