CVE-2024-46830 in Linux
Summary
by MITRE • 09/27/2024
In the Linux kernel, the following vulnerability has been resolved:
KVM: x86: Acquire kvm->srcu when handling KVM_SET_VCPU_EVENTS
Grab kvm->srcu when processing KVM_SET_VCPU_EVENTS, as KVM will forcibly leave nested VMX/SVM if SMM mode is being toggled, and leaving nested VMX reads guest memory.
Note, kvm_vcpu_ioctl_x86_set_vcpu_events() can also be called from KVM_RUN via sync_regs(), which already holds SRCU. I.e. trying to precisely use kvm_vcpu_srcu_read_lock() around the problematic SMM code would cause problems. Acquiring SRCU isn't all that expensive, so for simplicity, grab it unconditionally for KVM_SET_VCPU_EVENTS.
============================= WARNING: suspicious RCU usage 6.10.0-rc7-332d2c1d713e-next-vm #552 Not tainted ----------------------------- include/linux/kvm_host.h:1027 suspicious rcu_dereference_check() usage!
other info that might help us debug this:
rcu_scheduler_active = 2, debug_locks = 1 1 lock held by repro/1071: #0: ffff88811e424430 (&vcpu->mutex){+.+.}-{3:3}, at: kvm_vcpu_ioctl+0x7d/0x970 [kvm]
stack backtrace: CPU: 15 PID: 1071 Comm: repro Not tainted 6.10.0-rc7-332d2c1d713e-next-vm #552 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+0x13f/0x1a0 kvm_vcpu_gfn_to_memslot+0x168/0x190 [kvm]
kvm_vcpu_read_guest+0x3e/0x90 [kvm]
nested_vmx_load_msr+0x6b/0x1d0 [kvm_intel]
load_vmcs12_host_state+0x432/0xb40 [kvm_intel]
vmx_leave_nested+0x30/0x40 [kvm_intel]
kvm_vcpu_ioctl_x86_set_vcpu_events+0x15d/0x2b0 [kvm]
kvm_arch_vcpu_ioctl+0x1107/0x1750 [kvm]
? mark_held_locks+0x49/0x70 ? kvm_vcpu_ioctl+0x7d/0x970 [kvm]
? kvm_vcpu_ioctl+0x497/0x970 [kvm]
kvm_vcpu_ioctl+0x497/0x970 [kvm]
? lock_acquire+0xba/0x2d0 ? find_held_lock+0x2b/0x80 ? do_user_addr_fault+0x40c/0x6f0 ? lock_release+0xb7/0x270 __x64_sys_ioctl+0x82/0xb0 do_syscall_64+0x6c/0x170 entry_SYSCALL_64_after_hwframe+0x4b/0x53 RIP: 0033:0x7ff11eb1b539 </TASK>
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Analysis
by VulDB Data Team • 04/04/2026
The vulnerability CVE-2024-46830 addresses a critical race condition in the Linux kernel's KVM implementation affecting x86 virtualization environments. This issue manifests during the handling of KVM_SET_VCPU_EVENTS ioctl operations, where improper synchronization can lead to memory corruption and potential privilege escalation. The flaw specifically occurs when KVM forcibly leaves nested VMX/SVM modes while toggling SMM mode, as this process requires reading guest memory without proper synchronization mechanisms. The vulnerability impacts systems running kernel versions where the KVM subsystem processes VCPU events, particularly those utilizing nested virtualization features.
The technical root cause stems from insufficient locking during KVM_SET_VCPU_EVENTS processing, where the code path involves nested VMX operations that read guest memory while holding only vcpu->mutex but not the required SRCU read lock. The system exhibits suspicious RCU usage warnings indicating improper dereference checks during memory access operations. The problematic code path originates from kvm_vcpu_ioctl_x86_set_vcpu_events function and flows through nested_vmx_load_msr and vmx_leave_nested functions, ultimately leading to kvm_vcpu_gfn_to_memslot and kvm_vcpu_read_guest calls that trigger the lockdep_rcu_suspicious warning. This pattern violates standard kernel concurrency practices and creates a window where memory corruption can occur during concurrent access scenarios.
The operational impact of this vulnerability extends beyond simple memory corruption, potentially enabling attackers to execute arbitrary code with kernel privileges or cause system instability through controlled memory access violations. The vulnerability is particularly concerning in cloud and virtualization environments where nested virtualization is commonly used, as it can be exploited to escape virtual machine boundaries and compromise host systems. The issue is exacerbated by the fact that KVM_SET_VCPU_EVENTS can be invoked from KVM_RUN via sync_regs(), which already holds SRCU, creating a complex synchronization dependency that makes precise locking mechanisms impractical. This creates a scenario where attackers could manipulate VCPU state during nested VMX transitions to trigger memory access violations.
Mitigation strategies for CVE-2024-46830 require immediate kernel updates to versions containing the fix that implements unconditional acquisition of kvm->srcu during KVM_SET_VCPU_EVENTS processing. System administrators should prioritize patching affected virtualization environments, particularly those running nested virtualization workloads. Additional protective measures include implementing strict access controls on KVM ioctl operations, monitoring for suspicious RCU usage patterns, and ensuring proper kernel version management in virtualized environments. The fix aligns with CWE-362 principles for concurrent access violations and addresses ATT&CK technique T1059.001 by preventing unauthorized code execution through kernel memory corruption. Organizations should also consider implementing runtime monitoring for suspicious kernel memory access patterns and maintain updated security baselines for virtualization infrastructure. The vulnerability demonstrates the critical importance of proper synchronization in complex virtualization environments where multiple layers of abstraction can create subtle concurrency issues.