amd_iommu: Bound IVHD device-entry parsing

[kbowling]

Summary

Validate the IVRS table and every subtable length before using either
to form iterator bounds. Reject truncated typed IVHD blocks instead of
passing them to a type-specific callback.

Within each IVHD payload, correct the lower-bound comparison for
extended range entries and validate fixed-size entries, paired range
terminators, the fixed HID body, and the variable HID UID before
dereferencing or advancing. Malformed firmware can no longer drive
either iterator beyond its enclosing object.

MFC after:      2 weeks

[kib]

sys/x86/iommu/amd_drv.c

708

I do not like repeating the list of supported types of entries twice. Why cannot the check for the length embedded into the corresponding handler directly?

[kib]

sys/x86/iommu/amd_drv.c

135

Why do you check this only for the requested type?