{
"dataType": "CVE_RECORD",
"dataVersion": "5.2",
"cveMetadata": {
"cveId": "CVE-2026-23005",
"assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"state": "PUBLISHED",
"assignerShortName": "Linux",
"dateReserved": "2026-01-13T15:37:45.939Z",
"datePublished": "2026-01-25T14:36:19.021Z",
"dateUpdated": "2026-07-14T12:45:44.645Z"
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"shortName": "Linux",
"dateUpdated": "2026-05-11T21:58:09.790Z"
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"descriptions": [
{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nx86/fpu: Clear XSTATE_BV[i] in guest XSAVE state whenever XFD[i]=1\n\nWhen loading guest XSAVE state via KVM_SET_XSAVE, and when updating XFD in\nresponse to a guest WRMSR, clear XFD-disabled features in the saved (or to\nbe restored) XSTATE_BV to ensure KVM doesn't attempt to load state for\nfeatures that are disabled via the guest's XFD. Because the kernel\nexecutes XRSTOR with the guest's XFD, saving XSTATE_BV[i]=1 with XFD[i]=1\nwill cause XRSTOR to #NM and panic the kernel.\n\nE.g. if fpu_update_guest_xfd() sets XFD without clearing XSTATE_BV:\n\n ------------[ cut here ]------------\n WARNING: arch/x86/kernel/traps.c:1524 at exc_device_not_available+0x101/0x110, CPU#29: amx_test/848\n Modules linked in: kvm_intel kvm irqbypass\n CPU: 29 UID: 1000 PID: 848 Comm: amx_test Not tainted 6.19.0-rc2-ffa07f7fd437-x86_amx_nm_xfd_non_init-vm #171 NONE\n Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015\n RIP: 0010:exc_device_not_available+0x101/0x110\n Call Trace:\n \n asm_exc_device_not_available+0x1a/0x20\n RIP: 0010:restore_fpregs_from_fpstate+0x36/0x90\n switch_fpu_return+0x4a/0xb0\n kvm_arch_vcpu_ioctl_run+0x1245/0x1e40 [kvm]\n kvm_vcpu_ioctl+0x2c3/0x8f0 [kvm]\n __x64_sys_ioctl+0x8f/0xd0\n do_syscall_64+0x62/0x940\n entry_SYSCALL_64_after_hwframe+0x4b/0x53\n \n ---[ end trace 0000000000000000 ]---\n\nThis can happen if the guest executes WRMSR(MSR_IA32_XFD) to set XFD[18] = 1,\nand a host IRQ triggers kernel_fpu_begin() prior to the vmexit handler's\ncall to fpu_update_guest_xfd().\n\nand if userspace stuffs XSTATE_BV[i]=1 via KVM_SET_XSAVE:\n\n ------------[ cut here ]------------\n WARNING: arch/x86/kernel/traps.c:1524 at exc_device_not_available+0x101/0x110, CPU#14: amx_test/867\n Modules linked in: kvm_intel kvm irqbypass\n CPU: 14 UID: 1000 PID: 867 Comm: amx_test Not tainted 6.19.0-rc2-2dace9faccd6-x86_amx_nm_xfd_non_init-vm #168 NONE\n Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015\n RIP: 0010:exc_device_not_available+0x101/0x110\n Call Trace:\n \n asm_exc_device_not_available+0x1a/0x20\n RIP: 0010:restore_fpregs_from_fpstate+0x36/0x90\n fpu_swap_kvm_fpstate+0x6b/0x120\n kvm_load_guest_fpu+0x30/0x80 [kvm]\n kvm_arch_vcpu_ioctl_run+0x85/0x1e40 [kvm]\n kvm_vcpu_ioctl+0x2c3/0x8f0 [kvm]\n __x64_sys_ioctl+0x8f/0xd0\n do_syscall_64+0x62/0x940\n entry_SYSCALL_64_after_hwframe+0x4b/0x53\n \n ---[ end trace 0000000000000000 ]---\n\nThe new behavior is consistent with the AMX architecture. Per Intel's SDM,\nXSAVE saves XSTATE_BV as '0' for components that are disabled via XFD\n(and non-compacted XSAVE saves the initial configuration of the state\ncomponent):\n\n If XSAVE, XSAVEC, XSAVEOPT, or XSAVES is saving the state component i,\n the instruction does not generate #NM when XCR0[i] = IA32_XFD[i] = 1;\n instead, it operates as if XINUSE[i] = 0 (and the state component was\n in its initial state): it saves bit i of XSTATE_BV field of the XSAVE\n header as 0; in addition, XSAVE saves the initial configuration of the\n state component (the other instructions do not save state component i).\n\nAlternatively, KVM could always do XRSTOR with XFD=0, e.g. by using\na constant XFD based on the set of enabled features when XSAVEing for\na struct fpu_guest. However, having XSTATE_BV[i]=1 for XFD-disabled\nfeatures can only happen in the above interrupt case, or in similar\nscenarios involving preemption on preemptible kernels, because\nfpu_swap_kvm_fpstate()'s call to save_fpregs_to_fpstate() saves the\noutgoing FPU state with the current XFD; and that is (on all but the\nfirst WRMSR to XFD) the guest XFD.\n\nTherefore, XFD can only go out of sync with XSTATE_BV in the above\ninterrupt case, or in similar scenarios involving preemption on\npreemptible kernels, and it we can consider it (de facto) part of KVM\nABI that KVM_GET_XSAVE returns XSTATE_BV[i]=0 for XFD-disabled features.\n\n[Move clea\n---truncated---"
}
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"title": "x86/fpu: Clear XSTATE_BV[i] in guest XSAVE state whenever XFD[i]=1",
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