KVM: x86/hyper-v: Skip non-canonical addresses during PV TLB flush
- Published
- Last modified
- Where the record stands: published, rejected by its publisher, or superseded by another id.What do these mean? →
- published
- Whether CISA lists it in its Known Exploited Vulnerabilities catalog: proof that attackers are using it.What do these mean? →
- Not listed in CISA KEV
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
Summary
In the Linux kernel, the following vulnerability has been resolved: KVM: x86/hyper-v: Skip non-canonical addresses during PV TLB flush In KVM guests with Hyper-V hypercalls enabled, the hypercalls HVCALL_FLUSH_VIRTUAL_ADDRESS_LIST and HVCALL_FLUSH_VIRTUAL_ADDRESS_LIST_EX allow a guest to request invalidation of portions of a virtual TLB. For this, the hypercall parameter includes a list of GVAs that are supposed to be invalidated. However, when non-canonical GVAs are passed, there is currently no filtering in place and they are eventually passed to checked invocations of INVVPID on Intel / INVLPGA on AMD. While AMD's INVLPGA silently ignores non-canonical addresses (effectively a no-op), Intel's INVVPID explicitly signals VM-Fail and ultimately triggers the WARN_ONCE in invvpid_error(): invvpid failed: ext=0x0 vpid=1 gva=0xaaaaaaaaaaaaa000 WARNING: CPU: 6 PID: 326 at arch/x86/kvm/vmx/vmx.c:482 invvpid_error+0x91/0xa0 [kvm_intel] Modules linked in: kvm_intel kvm 9pnet_virtio irqbypass fuse CPU: 6 UID: 0 PID: 326 Comm: kvm-vm Not tainted 6.15.0 #14 PREEMPT(voluntary) RIP: 0010:invvpid_error+0x91/0xa0 [kvm_intel] Call Trace: vmx_flush_tlb_gva+0x320/0x490 [kvm_intel] kvm_hv_vcpu_flush_tlb+0x24f/0x4f0 [kvm] kvm_arch_vcpu_ioctl_run+0x3013/0x5810 [kvm] Hyper-V documents that invalid GVAs (those that are beyond a partition's GVA space) are to be ignored. While not completely clear whether this ruling also applies to non-canonical GVAs, it is likely fine to make that assumption, and manual testing on Azure confirms "real" Hyper-V interprets the specification in the same way. Skip non-canonical GVAs when processing the list of address to avoid tripping the INVVPID failure. Alternatively, KVM could filter out "bad" GVAs before inserting into the FIFO, but practically speaking the only downside of pushing validation to the final processing is that doing so is suboptimal for the guest, and no well-behaved guest will request TLB flushes for non-canonical addresses.
Timeline
- CVE published
- Record last updated
Affected versions
- Linux Linux
Version range not reported
- Linux Linux
6.2