CVE-2025-23141 in Linux
Summary
by MITRE • 05/01/2025
In the Linux kernel, the following vulnerability has been resolved:
KVM: x86: Acquire SRCU in KVM_GET_MP_STATE to protect guest memory accesses
Acquire a lock on kvm->srcu when userspace is getting MP state to handle a rather extreme edge case where "accepting" APIC events, i.e. processing pending INIT or SIPI, can trigger accesses to guest memory. If the vCPU is in L2 with INIT *and* a TRIPLE_FAULT request pending, then getting MP state will trigger a nested VM-Exit by way of ->check_nested_events(), and emuating the nested VM-Exit can access guest memory.
The splat was originally hit by syzkaller on a Google-internal kernel, and reproduced on an upstream kernel by hacking the triple_fault_event_test selftest to stuff a pending INIT, store an MSR on VM-Exit (to generate a memory access on VMX), and do vcpu_mp_state_get() to trigger the scenario.
============================= WARNING: suspicious RCU usage 6.14.0-rc3-b112d356288b-vmx/pi_lockdep_false_pos-lock #3 Not tainted ----------------------------- include/linux/kvm_host.h:1058 suspicious rcu_dereference_check() usage!
other info that might help us debug this:
rcu_scheduler_active = 2, debug_locks = 1 1 lock held by triple_fault_ev/1256: #0: ffff88810df5a330 (&vcpu->mutex){+.+.}-{4:4}, at: kvm_vcpu_ioctl+0x8b/0x9a0 [kvm]
stack backtrace: CPU: 11 UID: 1000 PID: 1256 Comm: triple_fault_ev Not tainted 6.14.0-rc3-b112d356288b-vmx #3 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 Call Trace: <TASK> dump_stack_lvl+0x7f/0x90 lockdep_rcu_suspicious+0x144/0x190 kvm_vcpu_gfn_to_memslot+0x156/0x180 [kvm]
kvm_vcpu_read_guest+0x3e/0x90 [kvm]
read_and_check_msr_entry+0x2e/0x180 [kvm_intel]
__nested_vmx_vmexit+0x550/0xde0 [kvm_intel]
kvm_check_nested_events+0x1b/0x30 [kvm]
kvm_apic_accept_events+0x33/0x100 [kvm]
kvm_arch_vcpu_ioctl_get_mpstate+0x30/0x1d0 [kvm]
kvm_vcpu_ioctl+0x33e/0x9a0 [kvm]
__x64_sys_ioctl+0x8b/0xb0 do_syscall_64+0x6c/0x170 entry_SYSCALL_64_after_hwframe+0x4b/0x53 </TASK>
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Analysis
by VulDB Data Team • 11/07/2025
The vulnerability described in CVE-2025-23141 affects the Linux kernel's KVM implementation on x86 architectures, specifically within the handling of nested virtualization scenarios. This issue arises when userspace attempts to retrieve the multiprocessor state of a virtual CPU through the KVM_GET_MP_STATE ioctl, which triggers an edge case involving APIC event processing and guest memory access. The root cause lies in the improper synchronization of memory access operations during nested VM-exits, where guest memory accesses can occur without proper protection mechanisms. The vulnerability was initially discovered through automated testing by syzkaller on a Google-internal kernel and subsequently reproduced on upstream kernels, demonstrating its potential impact across different kernel versions.
The technical flaw manifests in the absence of proper SRCU (Sleepable Read-Copy Update) locking when accessing guest memory during MP state retrieval operations. When a vCPU is operating in nested virtualization mode with pending INIT events and a TRIPLE_FAULT request, the process of checking nested events can trigger a VM-exit that subsequently emulates memory accesses to guest pages. The kernel's current implementation fails to acquire the necessary kvm->srcu lock during this critical path, leading to potential race conditions and memory access violations. The stack trace reveals that the issue occurs during nested VM-exit emulation in the __nested_vmx_vmexit function, where kvm_vcpu_read_guest attempts to access guest memory without proper locking, triggering a suspicious RCU usage warning from the kernel's lockdep subsystem.
The operational impact of this vulnerability extends beyond simple memory access violations to potentially enable privilege escalation or system instability within virtualized environments. The scenario described requires specific conditions involving nested virtualization, pending INIT events, and memory access patterns during VM-exit handling, making it an extreme edge case but one that could be exploited by malicious actors with access to virtualized systems. The vulnerability affects systems using KVM with Intel VT-x virtualization capabilities, particularly those running nested virtualization workloads where multiple levels of VM-exits occur. The lockdep subsystem's warning indicates that the kernel's RCU subsystem detected potentially unsafe memory access patterns, suggesting that this could lead to memory corruption or data integrity issues.
Mitigation strategies for this vulnerability involve implementing proper SRCU locking mechanisms during the KVM_GET_MP_STATE operation to ensure that guest memory accesses are properly synchronized. The fix requires acquiring the kvm->srcu lock before processing APIC events and guest memory accesses during MP state retrieval, which prevents concurrent modifications to guest memory structures. System administrators should ensure that all KVM-based virtualization environments are updated to kernel versions containing the patched implementation. Organizations running nested virtualization workloads should particularly monitor their systems for this vulnerability, as the conditions required for exploitation are more likely to occur in complex virtualization setups. The fix aligns with security best practices for concurrent access control and memory management in virtualized environments, addressing the underlying CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization) vulnerability pattern. This issue also relates to ATT&CK technique T1059.001 (Command and Scripting Interpreter: PowerShell) and T1078.004 (Valid Accounts: Cloud Accounts) in the context of privilege escalation within virtualized environments, though the primary concern is the kernel-level memory safety violation rather than direct account compromise.