Dear Syzkaller Group and Linux Kernel Upstream,
I am writing to report an intermittent issue that appears when running
Syzkaller inside a Docker container with privileged KVM access. The
host system becomes unresponsive after prolonged fuzzing, and I hope
your insights can help identify the root cause.
Environment Details:
- Host Machine:
- OS: Ubuntu 20.04.6 LTS
- Kernel: x86_64 Linux 5.15.0-136-generic
- CPU: Intel Xeon Platinum 8268 @ 192×3.9GHz
- Docker Container:
- Base Image: Ubuntu 22.04 (qgrain/kernel-fuzz:v1)
- Syzkaller Version: commit 4121cf9 (20250217)
- Startup Command: docker run -itd -p 29400:22 -v
/PATH/KERNELS:/root/kernels --name NAME --privileged=true
qgrain/kernel-fuzz:v1
After the fuzzing instances had been running for an extended period,
the host system became completely inaccessible (e.g., SSH connections
failed). Through IPMI, I observed the following repeated log messages
on the virtual terminal:
[244053.888249] kvm [3867]: vcpu2, guest pF: 0xffffffff813008ac
vmx_set_jsr: BTF ln_inA2_DEBUGTRLSR 0x2, nop
[244053.938264] kvm [3867]: vcpu3, guest pF: 0xffffffff813008ac
vmx_set_jsr: BTF ln_inA2_DEBUGTRLSR 0x2, nop
[244053.960191] kvm [3867]: vcpu0, guest pF: 0xffffffff813008ac
vmx_set_jsr: BTF ln_inA2_DEBUGTRLSR 0x2, nop
[244053.992411] kvm [3867]: vcpu1, guest pF: 0xffffffff813008ac
vmx_set_jsr: BTF ln_inA2_DEBUGTRLSR 0x2, nop
[244075.149293] kvm [3882]: vcpu3, guest pF: 0xffffffff81300744
vmx_set_jsr: BTF ln_inA2_DEBUGTRLSR 0x2, nop
...
Speculation on Possible Causes:
- One possibility is that the long-term Syzkaller fuzzing workload has
generated test cases that trigger an edge-case bug in the host KVM
module. The repeated “guest pF” errors could indicate that a specific
sequence of guest instructions is not being handled correctly.
- Alternatively, prolonged high-load conditions from continuous
fuzzing might have exposed an unhandled kernel or hardware bug related
to virtualization—potentially in the CPU’s VMX or within the KVM
module itself.
I apologize for the limited diagnostic information available at this
time (find nothing relevant to KVM in system logs). The above
speculation is preliminary, and I am unsure whether the root cause
lies within the Syzkaller side or Kernel KVM side.
Thank you for your attention to this matter. I look forward to any
suggestions or questions you may have.
Best regards,
Zhiyu Zhang
