{"id":"CVE-2026-46295","state":"PUBLISHED","title":"KVM: x86: Do IRR scan in __kvm_apic_update_irr even if PIR is empty","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: x86: Do IRR scan in __kvm_apic_update_irr even if PIR is empty\n\nFall back to apic_find_highest_vector() when PID.ON is set but PIR\nturns out to be empty, to correctly report the highest pending interrupt\nfrom the existing IRR.\n\nIn a nested VM stress test, the following WARNING fires in\nvmx_check_nested_events() when kvm_cpu_has_interrupt() reports a pending\ninterrupt but the subsequent kvm_apic_has_interrupt() (which invokes\nvmx_sync_pir_to_irr() again) returns -1:\n\n  WARNING: CPU: 99 PID: 57767 at arch/x86/kvm/vmx/nested.c:4449 vmx_check_nested_events+0x6bf/0x6e0 [kvm_intel]\n  Call Trace:\n   kvm_check_and_inject_events\n   vcpu_enter_guest.constprop.0\n   vcpu_run\n   kvm_arch_vcpu_ioctl_run\n   kvm_vcpu_ioctl\n   __x64_sys_ioctl\n   do_syscall_64\n   entry_SYSCALL_64_after_hwframe\n\nThe root cause is a race between vmx_sync_pir_to_irr() on the target vCPU\nand __vmx_deliver_posted_interrupt() on a sender vCPU.  The sender\nperforms two individually-atomic operations that are not a single\ntransaction:\n\n  1. pi_test_and_set_pir(vector)  -- sets the PIR bit\n  2. pi_test_and_set_on()         -- sets PID.ON\n\nThe following interleaving triggers the bug:\n\n  Sender vCPU (IPI):              Target vCPU (1st sync_pir_to_irr):\n  B1: set PIR[vector]\n                                  A1: pi_clear_on()\n                                  A2: pi_harvest_pir() -> sees B1 bit\n                                  A3: xchg() -> consumes bit, PIR=0\n                                      (1st sync returns correct max_irr)\n  B2: set PID.ON = 1\n\n                                  Target vCPU (2nd sync_pir_to_irr):\n                                  C1: pi_test_on() -> TRUE (from B2)\n                                  C2: pi_clear_on() -> ON=0\n                                  C3: pi_harvest_pir() -> PIR empty\n                                  C4: *max_irr = -1, early return\n                                      IRR NOT SCANNED\n\nThe interrupt is not lost (it resides in the IRR from the first sync and\nis recovered on the next vcpu_enter_guest() iteration), but the incorrect\nmax_irr causes a spurious WARNING and a wasted L2 VM-Enter/VM-Exit cycle.","publishedAt":"2026-06-08T15:46:22.494Z","updatedAt":"2026-06-14T18:07:10.912Z","severity":null,"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"b41f8638b9d30fbe045b4ef83ff4136c56a57397","status":"affected","lessThan":"bb1703949dcaa9a49c338dee075f659f4634214d","versionType":"git"},{"version":"b41f8638b9d30fbe045b4ef83ff4136c56a57397","status":"affected","lessThan":"4b6b06a8b12bfd95f9015074b1430c1480908073","versionType":"git"},{"version":"b41f8638b9d30fbe045b4ef83ff4136c56a57397","status":"affected","lessThan":"33fd0ccd2590b470b65adcca288615ad3b5e3e06","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["arch/x86/kvm/lapic.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.16","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.16","versionType":"semver"},{"version":"6.18.30","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.0.7","status":"unaffected","lessThanOrEqual":"7.0.*","versionType":"semver"},{"version":"7.1","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/lapic.c"]}],"references":["https://git.kernel.org/stable/c/bb1703949dcaa9a49c338dee075f659f4634214d","https://git.kernel.org/stable/c/4b6b06a8b12bfd95f9015074b1430c1480908073","https://git.kernel.org/stable/c/33fd0ccd2590b470b65adcca288615ad3b5e3e06"],"weaknesses":[],"ingestedAt":"2026-10-29T20:12:07.131Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/46xxx/CVE-2026-46295.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-46295","state":"PUBLISHED","datePublished":"2026-06-08T15:46:22.494Z","dateUpdated":"2026-06-14T18:07:10.912Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-05-13T15:03:33.110Z"},"containers":{"cna":{"title":"KVM: x86: Do IRR scan in __kvm_apic_update_irr even if PIR is empty","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: x86: Do IRR scan in __kvm_apic_update_irr even if PIR is empty\n\nFall back to apic_find_highest_vector() when PID.ON is set but PIR\nturns out to be empty, to correctly report the highest pending interrupt\nfrom the existing IRR.\n\nIn a nested VM stress test, the following WARNING fires in\nvmx_check_nested_events() when kvm_cpu_has_interrupt() reports a pending\ninterrupt but the subsequent kvm_apic_has_interrupt() (which invokes\nvmx_sync_pir_to_irr() again) returns -1:\n\n  WARNING: CPU: 99 PID: 57767 at arch/x86/kvm/vmx/nested.c:4449 vmx_check_nested_events+0x6bf/0x6e0 [kvm_intel]\n  Call Trace:\n   kvm_check_and_inject_events\n   vcpu_enter_guest.constprop.0\n   vcpu_run\n   kvm_arch_vcpu_ioctl_run\n   kvm_vcpu_ioctl\n   __x64_sys_ioctl\n   do_syscall_64\n   entry_SYSCALL_64_after_hwframe\n\nThe root cause is a race between vmx_sync_pir_to_irr() on the target vCPU\nand __vmx_deliver_posted_interrupt() on a sender vCPU.  The sender\nperforms two individually-atomic operations that are not a single\ntransaction:\n\n  1. pi_test_and_set_pir(vector)  -- sets the PIR bit\n  2. pi_test_and_set_on()         -- sets PID.ON\n\nThe following interleaving triggers the bug:\n\n  Sender vCPU (IPI):              Target vCPU (1st sync_pir_to_irr):\n  B1: set PIR[vector]\n                                  A1: pi_clear_on()\n                                  A2: pi_harvest_pir() -> sees B1 bit\n                                  A3: xchg() -> consumes bit, PIR=0\n                                      (1st sync returns correct max_irr)\n  B2: set PID.ON = 1\n\n                                  Target vCPU (2nd sync_pir_to_irr):\n                                  C1: pi_test_on() -> TRUE (from B2)\n                                  C2: pi_clear_on() -> ON=0\n                                  C3: pi_harvest_pir() -> PIR empty\n                                  C4: *max_irr = -1, early return\n                                      IRR NOT SCANNED\n\nThe interrupt is not lost (it resides in the IRR from the first sync and\nis recovered on the next vcpu_enter_guest() iteration), but the incorrect\nmax_irr causes a spurious WARNING and a wasted L2 VM-Enter/VM-Exit cycle."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"b41f8638b9d30fbe045b4ef83ff4136c56a57397","status":"affected","lessThan":"bb1703949dcaa9a49c338dee075f659f4634214d","versionType":"git"},{"version":"b41f8638b9d30fbe045b4ef83ff4136c56a57397","status":"affected","lessThan":"4b6b06a8b12bfd95f9015074b1430c1480908073","versionType":"git"},{"version":"b41f8638b9d30fbe045b4ef83ff4136c56a57397","status":"affected","lessThan":"33fd0ccd2590b470b65adcca288615ad3b5e3e06","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["arch/x86/kvm/lapic.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.16","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.16","versionType":"semver"},{"version":"6.18.30","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.0.7","status":"unaffected","lessThanOrEqual":"7.0.*","versionType":"semver"},{"version":"7.1","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/lapic.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/bb1703949dcaa9a49c338dee075f659f4634214d"},{"url":"https://git.kernel.org/stable/c/4b6b06a8b12bfd95f9015074b1430c1480908073"},{"url":"https://git.kernel.org/stable/c/33fd0ccd2590b470b65adcca288615ad3b5e3e06"}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-06-14T18:07:10.912Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.16","versionEndExcluding":"6.18.30"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.16","versionEndExcluding":"7.0.7"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.16","versionEndExcluding":"7.1"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}}}}}