{"id":"CVE-2026-68093","state":"PUBLISHED","title":"KVM: SVM: Bump asid_generation on CPU online to avoid ASID collision after hotplug","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: SVM: Bump asid_generation on CPU online to avoid ASID collision after hotplug\n\nIf a vCPU stays scheduled out (or blocked) while the last pCPU it ran\non goes through a hotplug cycle (online->offline->online), and the vCPU\nthen resumes execution on the same pCPU, then it is possible for it to\nrun with an ASID that has now been assigned to a different vCPU,\nresulting in stale TLB translations being used.\n\nsvm_enable_virtualization_cpu() resets asid_generation to 1 and sets\nnext_asid to max_asid + 1 on every CPU online event, including hotplug\ncycles.  Because next_asid starts beyond the pool boundary, the first\ncall to new_asid() after an online event always wraps the pool,\nincrementing asid_generation to 2 and assigning ASIDs starting from\nmin_asid.\n\nConsider two vCPUs from different VMs, vCPU-A pinned to CPU-X holding\nasid_generation=2 and ASID=N from before the hotplug event:\n\n  1. CPU-X goes offline and back online: asid_generation resets to 1,\n     next_asid = max_asid + 1.\n\n  2. One or more vCPUs migrate to CPU-X and call new_asid(), wrapping\n     the pool and consuming ASIDs starting from min_asid.  Eventually\n     vCPU-B from a different VM is assigned asid_generation=2, ASID=N\n     — the same ASID that vCPU-A held before the hotplug.\n\n  3. vCPU-A enters pre_svm_run() on CPU-X: current_vmcb->cpu is\n     unchanged so the migration branch is skipped.  Its saved\n     asid_generation=2 matches sd->asid_generation=2, so the generation\n     check silently passes and vCPU-A continues running with ASID=N —\n     the same ASID just freshly assigned to vCPU-B.\n\nBoth vCPUs from different VMs now run on CPU-X with the same ASID,\ncausing them to share NPT TLB entries and producing stale translations.\n\nThe collision manifests as a KVM internal error (Suberror: 1, emulation\nfailure).  The NPT page fault reports a faulting GPA far outside the\nVM's physical memory range — a sign of stale TLB translations being\nused.  KVM falls back to instruction emulation, which fails on\nFPU/XSave instructions (XRSTOR, STMXCSR) that the emulator does not\nimplement.\n\nFix this by incrementing asid_generation instead of resetting it to 1\nin svm_enable_virtualization_cpu().  On module load, asid_generation\nstarts at 0 (memset) and the increment produces 1, identical to the\nold behaviour.  On subsequent hotplug cycles the generation advances\nbeyond any value a vCPU previously observed on this CPU, so the\ngeneration check in pre_svm_run() reliably forces new_asid() on every\nvCPU after every hotplug cycle.","publishedAt":"2026-08-10T11:58:05.933Z","updatedAt":"2026-08-19T16:29:15.060Z","severity":null,"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"774c47f1d78e373a6bd2964f4e278d1ce26c21cb","status":"affected","lessThan":"2028b81321dc757b6875b99c10d908e349c141e2","versionType":"git"},{"version":"774c47f1d78e373a6bd2964f4e278d1ce26c21cb","status":"affected","lessThan":"60283726f2845bd78b95efbd0e50b93944780477","versionType":"git"},{"version":"774c47f1d78e373a6bd2964f4e278d1ce26c21cb","status":"affected","lessThan":"7508916b4b55d6f5ecc68cd09774dabd3a6b4440","versionType":"git"},{"version":"774c47f1d78e373a6bd2964f4e278d1ce26c21cb","status":"affected","lessThan":"0f33b1c457c2199ed130b92cc2ff363a3f7b9415","versionType":"git"},{"version":"774c47f1d78e373a6bd2964f4e278d1ce26c21cb","status":"affected","lessThan":"6b542d116acecb83a1ca34e8eace304cff6a4ec9","versionType":"git"},{"version":"774c47f1d78e373a6bd2964f4e278d1ce26c21cb","status":"affected","lessThan":"25f744ffa0c8e799e06250ce2e618367b166b0d4","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["arch/x86/kvm/svm/svm.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"2.6.21","status":"affected"},{"version":"0","status":"unaffected","lessThan":"2.6.21","versionType":"semver"},{"version":"6.1.183","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.148","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.101","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.42","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.1.6","status":"unaffected","lessThanOrEqual":"7.1.*","versionType":"semver"},{"version":"7.2","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["arch/x86/kvm/svm/svm.c"]}],"references":["https://git.kernel.org/stable/c/2028b81321dc757b6875b99c10d908e349c141e2","https://git.kernel.org/stable/c/60283726f2845bd78b95efbd0e50b93944780477","https://git.kernel.org/stable/c/7508916b4b55d6f5ecc68cd09774dabd3a6b4440","https://git.kernel.org/stable/c/0f33b1c457c2199ed130b92cc2ff363a3f7b9415","https://git.kernel.org/stable/c/6b542d116acecb83a1ca34e8eace304cff6a4ec9","https://git.kernel.org/stable/c/25f744ffa0c8e799e06250ce2e618367b166b0d4"],"weaknesses":[],"ingestedAt":"2026-10-29T20:12:49.727Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/68xxx/CVE-2026-68093.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-68093","state":"PUBLISHED","datePublished":"2026-08-10T11:58:05.933Z","dateUpdated":"2026-08-19T16:29:15.060Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-07-30T09:28:09.367Z"},"containers":{"cna":{"title":"KVM: SVM: Bump asid_generation on CPU online to avoid ASID collision after hotplug","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: SVM: Bump asid_generation on CPU online to avoid ASID collision after hotplug\n\nIf a vCPU stays scheduled out (or blocked) while the last pCPU it ran\non goes through a hotplug cycle (online->offline->online), and the vCPU\nthen resumes execution on the same pCPU, then it is possible for it to\nrun with an ASID that has now been assigned to a different vCPU,\nresulting in stale TLB translations being used.\n\nsvm_enable_virtualization_cpu() resets asid_generation to 1 and sets\nnext_asid to max_asid + 1 on every CPU online event, including hotplug\ncycles.  Because next_asid starts beyond the pool boundary, the first\ncall to new_asid() after an online event always wraps the pool,\nincrementing asid_generation to 2 and assigning ASIDs starting from\nmin_asid.\n\nConsider two vCPUs from different VMs, vCPU-A pinned to CPU-X holding\nasid_generation=2 and ASID=N from before the hotplug event:\n\n  1. CPU-X goes offline and back online: asid_generation resets to 1,\n     next_asid = max_asid + 1.\n\n  2. One or more vCPUs migrate to CPU-X and call new_asid(), wrapping\n     the pool and consuming ASIDs starting from min_asid.  Eventually\n     vCPU-B from a different VM is assigned asid_generation=2, ASID=N\n     — the same ASID that vCPU-A held before the hotplug.\n\n  3. vCPU-A enters pre_svm_run() on CPU-X: current_vmcb->cpu is\n     unchanged so the migration branch is skipped.  Its saved\n     asid_generation=2 matches sd->asid_generation=2, so the generation\n     check silently passes and vCPU-A continues running with ASID=N —\n     the same ASID just freshly assigned to vCPU-B.\n\nBoth vCPUs from different VMs now run on CPU-X with the same ASID,\ncausing them to share NPT TLB entries and producing stale translations.\n\nThe collision manifests as a KVM internal error (Suberror: 1, emulation\nfailure).  The NPT page fault reports a faulting GPA far outside the\nVM's physical memory range — a sign of stale TLB translations being\nused.  KVM falls back to instruction emulation, which fails on\nFPU/XSave instructions (XRSTOR, STMXCSR) that the emulator does not\nimplement.\n\nFix this by incrementing asid_generation instead of resetting it to 1\nin svm_enable_virtualization_cpu().  On module load, asid_generation\nstarts at 0 (memset) and the increment produces 1, identical to the\nold behaviour.  On subsequent hotplug cycles the generation advances\nbeyond any value a vCPU previously observed on this CPU, so the\ngeneration check in pre_svm_run() reliably forces new_asid() on every\nvCPU after every hotplug cycle."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"774c47f1d78e373a6bd2964f4e278d1ce26c21cb","status":"affected","lessThan":"2028b81321dc757b6875b99c10d908e349c141e2","versionType":"git"},{"version":"774c47f1d78e373a6bd2964f4e278d1ce26c21cb","status":"affected","lessThan":"60283726f2845bd78b95efbd0e50b93944780477","versionType":"git"},{"version":"774c47f1d78e373a6bd2964f4e278d1ce26c21cb","status":"affected","lessThan":"7508916b4b55d6f5ecc68cd09774dabd3a6b4440","versionType":"git"},{"version":"774c47f1d78e373a6bd2964f4e278d1ce26c21cb","status":"affected","lessThan":"0f33b1c457c2199ed130b92cc2ff363a3f7b9415","versionType":"git"},{"version":"774c47f1d78e373a6bd2964f4e278d1ce26c21cb","status":"affected","lessThan":"6b542d116acecb83a1ca34e8eace304cff6a4ec9","versionType":"git"},{"version":"774c47f1d78e373a6bd2964f4e278d1ce26c21cb","status":"affected","lessThan":"25f744ffa0c8e799e06250ce2e618367b166b0d4","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["arch/x86/kvm/svm/svm.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"2.6.21","status":"affected"},{"version":"0","status":"unaffected","lessThan":"2.6.21","versionType":"semver"},{"version":"6.1.183","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.148","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.101","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.42","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.1.6","status":"unaffected","lessThanOrEqual":"7.1.*","versionType":"semver"},{"version":"7.2","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["arch/x86/kvm/svm/svm.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/2028b81321dc757b6875b99c10d908e349c141e2"},{"url":"https://git.kernel.org/stable/c/60283726f2845bd78b95efbd0e50b93944780477"},{"url":"https://git.kernel.org/stable/c/7508916b4b55d6f5ecc68cd09774dabd3a6b4440"},{"url":"https://git.kernel.org/stable/c/0f33b1c457c2199ed130b92cc2ff363a3f7b9415"},{"url":"https://git.kernel.org/stable/c/6b542d116acecb83a1ca34e8eace304cff6a4ec9"},{"url":"https://git.kernel.org/stable/c/25f744ffa0c8e799e06250ce2e618367b166b0d4"}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-08-19T16:29:15.060Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.21","versionEndExcluding":"6.1.183"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.21","versionEndExcluding":"6.6.148"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.21","versionEndExcluding":"6.12.101"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.21","versionEndExcluding":"6.18.42"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.21","versionEndExcluding":"7.1.6"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"2.6.21","versionEndExcluding":"7.2"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}}}}}