KVM: nSVM: Raise #UD if unhandled VMMCALL isn't intercepted by L1

Summary

In the Linux kernel, the following vulnerability has been resolved: KVM: nSVM: Raise #UD if unhandled VMMCALL isn't intercepted by L1 Explicitly synthesize a #UD for VMMCALL if L2 is active, L1 does NOT want to intercept VMMCALL, nested_svm_l2_tlb_flush_enabled() is true, and the hypercall is something other than one of the supported Hyper-V hypercalls. When all of the above conditions are met, KVM will intercept VMMCALL but never forward it to L1, i.e. will let L2 make hypercalls as if it were L1. The TLFS says a whole lot of nothing about this scenario, so go with the architectural behavior, which says that VMMCALL #UDs if it's not intercepted. Opportunistically do a 2-for-1 stub trade by stub-ifying the new API instead of the helpers it uses. The last remaining "single" stub will soon be dropped as well. [sean: rewrite changelog and comment, tag for stable, remove defunct stubs]

Timeline

1. May 27, 2026, 12:58 PM UTCCVE published
2. Oct 16, 2026, 3:19 PM UTCCISA SSVC assessment

   Exploitation: none · Automatable: no · Technical impact: partial

3. Oct 21, 2026, 12:41 PM UTCRecord last updated

Affected versions

• Linux Linux

  From 3f4a812edf5cb0a50e65fbdfafdb3e688da18f16 · fixed in fcef67506c0234935cb0fb026740a637edb58d7c; From 3f4a812edf5cb0a50e65fbdfafdb3e688da18f16 · fixed in 924d721fae95687acedbaf624a094ed0e8b67104; From 3f4a812edf5cb0a50e65fbdfafdb3e688da18f16 · fixed in 009c0f726abeaa67aad1d96b883bdce01d405ce2; From 3f4a812edf5cb0a50e65fbdfafdb3e688da18f16 · fixed in 5fb4a5f361565f5b629d8a8fe5288ce8463c5727; From 3f4a812edf5cb0a50e65fbdfafdb3e688da18f16 · fixed in c36991c6f8d2ab56ee67aff04e3c357f45cfc76c

• Linux Linux

  6.2

• KernelLinux

  From 6.2.0 · fixed in 6.6.160; From 6.7.0 · fixed in 6.12.86; From 6.13.0 · fixed in 6.18.27; From 6.19.0 · fixed in 7.0.4

References 5