CVE-2023-52639 in Linux
Summary
by MITRE • 04/03/2024
In the Linux kernel, the following vulnerability has been resolved:
KVM: s390: vsie: fix race during shadow creation
Right now it is possible to see gmap->private being zero in kvm_s390_vsie_gmap_notifier resulting in a crash. This is due to the fact that we add gmap->private == kvm after creation:
static int acquire_gmap_shadow(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page) {
[...]
gmap = gmap_shadow(vcpu->arch.gmap, asce, edat); if (IS_ERR(gmap)) return PTR_ERR(gmap); gmap->private = vcpu->kvm;
Let children inherit the private field of the parent.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 03/17/2025
The vulnerability CVE-2023-52639 affects the Linux kernel's KVM implementation on s390 architecture systems, specifically within the virtual supervisor instruction execution subsystem. This issue represents a race condition during the creation of shadow virtual memory mappings that can lead to system crashes and potential privilege escalation. The flaw manifests when the gmap->private field becomes zero during the kvm_s390_vsie_gmap_notifier function execution, causing a kernel panic due to invalid memory access patterns.
The technical root cause lies in the improper initialization sequence of the gmap structure's private field within the acquire_gmap_shadow function. The kernel code creates a shadow gmap mapping using gmap_shadow() but only assigns the vcpu->kvm to gmap->private after the mapping is established. This timing issue creates a window where other threads or processes can access the gmap structure before the private field is properly set, leading to a null pointer dereference when the gmap notifier attempts to access the uninitialized field. This race condition specifically impacts the s390 virtualization subsystem where guest virtual machines interact with hypervisor memory management structures.
The operational impact of this vulnerability extends beyond simple system crashes to potentially compromise the integrity of virtualized environments. Attackers could exploit this race condition to cause denial of service against virtual machines or potentially escalate privileges within the hypervisor context. The vulnerability affects systems running Linux kernels with KVM virtualization enabled on s390 architecture, making it particularly concerning for mainframe virtualization environments and enterprise data centers that rely on IBM z/Architecture systems. The issue stems from a fundamental flaw in the memory management synchronization mechanisms within the virtualization layer, where proper initialization ordering is not enforced.
Mitigation strategies should focus on implementing proper synchronization mechanisms around the gmap creation and initialization process. System administrators should prioritize applying kernel updates that contain the patched code which ensures proper initialization ordering of the gmap->private field before making it accessible to other threads. The fix requires modifying the acquire_gmap_shadow function to initialize the private field before any potential access paths are established, preventing the race condition from occurring. Additionally, organizations should monitor for similar race conditions in other virtualization components and ensure proper implementation of the principle of least privilege for virtual machine operations. This vulnerability aligns with CWE-362, which addresses race conditions in concurrent programming, and maps to ATT&CK technique T1059.003 for privilege escalation through hypervisor vulnerabilities, highlighting the critical nature of proper memory management in virtualized environments.