CVE-2016-5412 in Linux
Summary
by MITRE
arch/powerpc/kvm/book3s_hv_rmhandlers.S in the Linux kernel through 4.7 on PowerPC platforms, when CONFIG_KVM_BOOK3S_64_HV is enabled, allows guest OS users to cause a denial of service (host OS infinite loop) by making a H_CEDE hypercall during the existence of a suspended transaction.
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Analysis
by VulDB Data Team • 09/13/2022
The vulnerability identified as CVE-2016-5412 resides within the Linux kernel's PowerPC implementation of the KVM hypervisor subsystem, specifically in the book3s_hv_rmhandlers.S file. This flaw affects Linux kernel versions through 4.7 and manifests when the CONFIG_KVM_BOOK3S_64_HV configuration option is enabled, creating a critical security issue that can be exploited by guest operating system users to induce a denial of service condition on the host system. The vulnerability operates through a specific interaction between the hypervisor's handling of hypercalls and the PowerPC processor's transactional memory capabilities, particularly when a suspended transaction exists during hypercall execution.
The technical mechanism of this vulnerability involves the H_CEDE hypercall, which is designed to suspend the guest processor and allow other threads to execute while the current thread is in a waiting state. When this hypercall is executed during the existence of a suspended transaction, the kernel's hypervisor implementation enters an infinite loop condition that prevents the host operating system from continuing normal operations. This occurs because the kernel's handling of the H_CEDE hypercall does not properly account for the presence of suspended transactions, leading to a recursive or circular execution path that cannot be resolved without manual intervention or system reboot. The flaw demonstrates a classic lack of proper state management in hypervisor code, where the system fails to properly transition between different processor states when handling specific hypercall sequences.
The operational impact of this vulnerability extends beyond simple denial of service, as it can effectively render the entire host system unusable to legitimate users while maintaining the malicious guest's ability to continue operating. This creates a significant risk for virtualized environments where multiple tenants share the same physical hardware, as a single compromised or malicious guest can potentially disrupt services for all other virtual machines running on the same host. The vulnerability is particularly concerning in cloud computing and data center environments where KVM-based virtualization is commonly deployed, as it provides a straightforward method for attackers to cause system-wide outages without requiring elevated privileges on the host system. The infinite loop condition consumes significant CPU resources and prevents the host from processing other legitimate requests, effectively creating a resource exhaustion scenario that can be exploited for sustained denial of service attacks.
Mitigation strategies for CVE-2016-5412 should focus on both immediate patching and architectural considerations for virtualized environments. The primary solution involves applying the kernel patches released by the Linux kernel development team that address the improper handling of H_CEDE hypercalls during suspended transaction states, which directly resolves the infinite loop condition. Organizations should also consider implementing additional monitoring and alerting mechanisms to detect unusual CPU utilization patterns that might indicate exploitation attempts, as well as ensuring that virtualization environments are properly isolated to limit the impact of potential attacks. From a security architecture perspective, this vulnerability highlights the importance of proper state management in hypervisor code and aligns with CWE-121, which addresses buffer overflow conditions that can lead to control flow modification. The flaw also demonstrates characteristics consistent with ATT&CK technique T1499, which involves the use of resource exhaustion to cause denial of service, making it a significant concern for organizations implementing virtualized security controls and maintaining availability for critical services.