CVE-2025-40102
Unknown Unknown - Not Provided
BaseFortify

Publication date: 2025-10-30

Last updated on: 2025-10-30

Assigner: kernel.org

Description
In the Linux kernel, the following vulnerability has been resolved: KVM: arm64: Prevent access to vCPU events before init Another day, another syzkaller bug. KVM erroneously allows userspace to pend vCPU events for a vCPU that hasn't been initialized yet, leading to KVM interpreting a bunch of uninitialized garbage for routing / injecting the exception. In one case the injection code and the hyp disagree on whether the vCPU has a 32bit EL1 and put the vCPU into an illegal mode for AArch64, tripping the BUG() in exception_target_el() during the next injection: kernel BUG at arch/arm64/kvm/inject_fault.c:40! Internal error: Oops - BUG: 00000000f2000800 [#1] SMP CPU: 3 UID: 0 PID: 318 Comm: repro Not tainted 6.17.0-rc4-00104-g10fd0285305d #6 PREEMPT Hardware name: linux,dummy-virt (DT) pstate: 21402009 (nzCv daif +PAN -UAO -TCO +DIT -SSBS BTYPE=--) pc : exception_target_el+0x88/0x8c lr : pend_serror_exception+0x18/0x13c sp : ffff800082f03a10 x29: ffff800082f03a10 x28: ffff0000cb132280 x27: 0000000000000000 x26: 0000000000000000 x25: ffff0000c2a99c20 x24: 0000000000000000 x23: 0000000000008000 x22: 0000000000000002 x21: 0000000000000004 x20: 0000000000008000 x19: ffff0000c2a99c20 x18: 0000000000000000 x17: 0000000000000000 x16: 0000000000000000 x15: 00000000200000c0 x14: 0000000000000000 x13: 0000000000000000 x12: 0000000000000000 x11: 0000000000000000 x10: 0000000000000000 x9 : 0000000000000000 x8 : ffff800082f03af8 x7 : 0000000000000000 x6 : 0000000000000000 x5 : ffff800080f621f0 x4 : 0000000000000000 x3 : 0000000000000000 x2 : 000000000040009b x1 : 0000000000000003 x0 : ffff0000c2a99c20 Call trace: exception_target_el+0x88/0x8c (P) kvm_inject_serror_esr+0x40/0x3b4 __kvm_arm_vcpu_set_events+0xf0/0x100 kvm_arch_vcpu_ioctl+0x180/0x9d4 kvm_vcpu_ioctl+0x60c/0x9f4 __arm64_sys_ioctl+0xac/0x104 invoke_syscall+0x48/0x110 el0_svc_common.constprop.0+0x40/0xe0 do_el0_svc+0x1c/0x28 el0_svc+0x34/0xf0 el0t_64_sync_handler+0xa0/0xe4 el0t_64_sync+0x198/0x19c Code: f946bc01 b4fffe61 9101e020 17fffff2 (d4210000) Reject the ioctls outright as no sane VMM would call these before KVM_ARM_VCPU_INIT anyway. Even if it did the exception would've been thrown away by the eventual reset of the vCPU's state.
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Meta Information
Published
2025-10-30
Last Modified
2025-10-30
Generated
2026-05-07
AI Q&A
2025-10-30
EPSS Evaluated
2026-05-05
NVD
CVE-2025-40102
Affected Vendors & Products
Showing 1 associated CPE
Vendor Product Version / Range
linux kernel *
Helpful Resources
Exploitability
CWE
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KEV
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CWE ID Description
CWE-UNKNOWN
Attack-Flow Graph
AI Powered Q&A
Can you explain this vulnerability to me?

This vulnerability in the Linux kernel's KVM on arm64 allows userspace to access and pend vCPU events for a virtual CPU (vCPU) that has not been initialized yet. This leads to KVM interpreting uninitialized garbage data when routing or injecting exceptions, which can cause the kernel to enter an illegal mode and trigger a kernel BUG or internal error. The issue arises because KVM does not reject ioctls related to vCPU events before the vCPU is properly initialized.


How can this vulnerability impact me? :

This vulnerability can cause the Linux kernel to crash or enter an unstable state due to illegal mode transitions and kernel BUGs triggered by uninitialized vCPU event handling. This could lead to denial of service or system instability in environments using KVM virtualization on arm64 architectures.


How can this vulnerability be detected on my network or system? Can you suggest some commands?

This vulnerability can be detected by monitoring the Linux kernel logs for the specific kernel BUG related to KVM arm64 vCPU events before initialization. Look for messages containing 'kernel BUG at arch/arm64/kvm/inject_fault.c:40' or 'Internal error: Oops - BUG' related to KVM. You can use the command `dmesg | grep 'kvm'` or `journalctl -k | grep 'kvm'` to search for such errors. Additionally, monitoring for crashes or oops messages related to KVM vCPU initialization may indicate exploitation attempts.


What immediate steps should I take to mitigate this vulnerability?

The immediate mitigation step is to ensure that the Linux kernel is updated to a version where this vulnerability is fixed. The fix involves rejecting ioctls that attempt to access or pend vCPU events before the vCPU has been initialized (i.e., before KVM_ARM_VCPU_INIT). Avoid running or allowing untrusted userspace code to interact with KVM vCPU ioctls before initialization. Applying the latest kernel patches that include this fix is the recommended action.


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