KVM: arm64: Handle VNCR TLB invalidation race with vcpu_put() VNCR unmapping

Summary

In the Linux kernel, the following vulnerability has been resolved: KVM: arm64: Handle VNCR TLB invalidation race with vcpu_put() VNCR unmapping While VNCR TLB invalidation always occurs under the MMU lock, vcpu_put() doesn't, while it unmaps the VNCR page. The problem is that the invalidation evaluates vncr_tlb::cpu to decide whether an unmapping needs to take place (cpu != -1) before performing it. On the other hand, this_cpu_reset_vncr_fixmap() unconditionally unmaps if L1_VNCR_MAPPED is set. These two obviously can race, with a TOCTOU pattern on the TLBI path, and a BUG_ON() on the vcpu_put() path. And the two can end-up calling vncr_fixmap(-1), with extra lethal effects. Move the reset of vncr_tlb::cpu to -1 to a common function, and make this update atomic so that only a single thread can reset the field and perform the corresponding unmap. The vcpu_put() still need to unconditionally unmap the current VNCR to close another ugly race. Finally, the assignment of vncr_tlb::cpu is moved to be kept in sync with the actual mapping, similar to L1_VNCR_MAPPED being set.

Timeline

1. Sep 16, 2026, 10:32 AM UTCCVE published
2. Oct 19, 2026, 8:54 AM UTCRecord last updated

Affected versions

• Linux Linux

  From 7270cc9157f474dfc46750a34c9d7defc686b2eb · fixed in 5cbd8761d001c11ada73b1753d772c4745a70e72; From 7270cc9157f474dfc46750a34c9d7defc686b2eb · fixed in 9065c1261f8a05c6a7a2d90048c7c0665ab2896d; From 7270cc9157f474dfc46750a34c9d7defc686b2eb · fixed in 38640bc32be3fcf9526d477155bc19d3f146231f

• Linux Linux

  6.16

• KernelLinux

  From 6.16.0 · fixed in 6.18.52; From 6.19.0 · fixed in 7.2.5

References 3