{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2026-99178", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2026-09-25T10:25:14.399Z", "datePublished": "2026-10-28T10:35:31.961Z", "dateUpdated": "2026-10-28T10:35:31.961Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-10-28T10:35:31.961Z" }, "descriptions": [ { "lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nx86/kvm: Don't consume async #PF flags on a kernel #PF in NMI context\n\nAn async #PF \"page not present\" event arrives through the #PF vector,\nand its reason sits in the per-CPU apf_reason.flags until\n__kvm_handle_async_pf() reads and clears it. If an NMI arrives after\nthe event is injected and before the #PF handler reads the flags, and\nthe NMI handler itself takes a #PF, that fault reads and clears the\nflags belonging to the #PF it interrupted. It then finds interrupts\ndisabled in the NMI context it interrupted, and panics:\n\n Kernel panic - not syncing: Host injected async #PF in interrupt\ndisabled region\n Call Trace:\n \n panic+0x52/0x60\n __kvm_handle_async_pf+0xb0/0xb0\n exc_page_fault+0x71/0xb0\n asm_exc_page_fault+0x27/0x30\n RIP: 0010:__get_user_nocheck_8+0x6/0x20\n perf_callchain_user+0x147/0x1a0\n get_perf_callchain+0x12d/0x1c0\n ...\n perf_event_nmi_handler+0x26/0x50\n exc_nmi+0xe8/0x110\n RIP: 0010:asm_exc_page_fault+0x0/0x30\n \n\nThe last RIP line shows the NMI landing on the first instruction of\nthe #PF entry. perf with user call chains takes such a fault: the\nsampling NMI walks the user stack with __get_user(), which faults when\na saved frame pointer is not a valid user address or the walk runs off\nthe top of the stack. The same window exists when KVM, running as an\nL1 hypervisor with DELIVERY_AS_PF_VMEXIT, reads the flags itself after\na #PF VM-exit.\n\nThe NMI entry code saves and restores CR2 for this nesting, but not the\nasync #PF reason. Andy Lutomirski described the race, with perf as the\nexample, when async #PF delivery was reworked in 2020 [1]. Saving and\nclearing the flags across the NMI, next to CR2, was discussed there but\nnot merged.\n\nSince that rework, Linux has stopped setting KVM_ASYNC_PF_SEND_ALWAYS,\nso the host delivers \"page not present\" only for user mode faults and\na kernel-mode fault in NMI context (including kernel-mode #MC and #DB)\ncannot be an async page fault. In that case, return without touching\nthe flags so that the interrupted handler finds them intact.\n\nTested on v7.3-rc5 in a 4-vCPU, 2 GiB guest restored from a snapshot\nwhose memory is served on demand through userfaultfd, so that reading\nit back takes async #PFs, while every thread samples hardware cycles\nwith user call chains and points its frame pointer at an unmapped page.\nWithout this patch the guest panicked as above in 3 of 3 runs. With it,\nthe guest survived 3 of 3 runs of 60 seconds, and the host counted\n148,441 to 153,334 kvm_async_pf_not_present events in the first 20\nseconds of each. On 6.18.50 the results were the same: the guest\npanicked without the patch and survived with it." } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "arch/x86/kernel/kvm.c" ], "versions": [ { "version": "1da177e4c3f41524e886b7f1b8a0c1fc7321cac2", "lessThan": "b77e9622bbade9812e2090c66d25c372f515e921", "status": "affected", "versionType": "git" }, { "version": "1da177e4c3f41524e886b7f1b8a0c1fc7321cac2", "lessThan": "f45ee1ff6358a22d7e22a4c53cb3148ea97b10d9", "status": "affected", "versionType": "git" }, { "version": "1da177e4c3f41524e886b7f1b8a0c1fc7321cac2", "lessThan": "81d99abe2bd81379abfb595e403bbbee6fbfc624", "status": "affected", "versionType": "git" }, { "version": "0", "lessThan": "6.18.59", "status": "affected", "versionType": "semver" }, { "version": "0", "lessThan": "7.2.13", "status": "affected", "versionType": "semver" } ] }, { "product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "arch/x86/kernel/kvm.c" ], "versions": [ { "version": "6.18.59", "lessThanOrEqual": "6.18.*", "status": "unaffected", "versionType": "semver" }, { "version": "7.2.13", "lessThanOrEqual": "7.2.*", "status": "unaffected", "versionType": "semver" }, { "version": "7.3", "lessThanOrEqual": "*", "status": "unaffected", "versionType": "original_commit_for_fix" } ] } ], "cpeApplicability": [ { "nodes": [ { "operator": "OR", "negate": false, "cpeMatch": [ { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionEndExcluding": "6.18.59" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionEndExcluding": "7.2.13" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionEndExcluding": "7.3" } ] } ] } ], "references": [ { "url": "https://git.kernel.org/stable/c/b77e9622bbade9812e2090c66d25c372f515e921" }, { "url": "https://git.kernel.org/stable/c/f45ee1ff6358a22d7e22a4c53cb3148ea97b10d9" }, { "url": "https://git.kernel.org/stable/c/81d99abe2bd81379abfb595e403bbbee6fbfc624" } ], "title": "x86/kvm: Don't consume async #PF flags on a kernel #PF in NMI context", "x_generator": { "engine": "bippy-1.2.0" } } } }