MitigationPolicies in KUSER_SHARED_DATA

The KUSER_SHARED_DATA structure defines the layout of a data area that the kernel places at a pre-set address for sharing with user-mode software. Windows 8 turns an old member named NXSupportPolicy at offset 0x02D5 into UCHAR bit fields in union with MitigationPolicies as some sort of collective name:

Mask Definition Versions
UCHAR NXSupportPolicy : 2;
6.2 and higher
UCHAR SEHValidationPolicy : 2;
6.2 and higher
UCHAR CurDirDevicesSkippedForDlls : 2;
6.2 and higher
UCHAR Reserved : 2;
6.2 and higher

Microsoft defines the following as allowed values for the NXSupportPolicy:

and another set for the SEHValidationPolicy: