CVE-2026-89917KVM: arm64: Handle VNCR TLB invalidation race with vcpu_put() VNCR unmapping

Official description

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.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/5cbd8761d001c11ada73b1753d772c4745a70e72
• https://git.kernel.org/stable/c/9065c1261f8a05c6a7a2d90048c7c0665ab2896d
• https://git.kernel.org/stable/c/38640bc32be3fcf9526d477155bc19d3f146231f