Firmware Interface Table

BIOS Specification

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ID 599500
Date 04/14/2023
Intel Confidential

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Document Table of Contents
Document Table of Contents
Legal Firmware Interface Table Introduction Summary of Key Requirements: FIT Pointer Firmware Interface Table
Legal
Firmware Interface Table Introduction
Summary of Key Requirements:
FIT Pointer
FIT Pointer FIT Pointer Rules
FIT Pointer Rules
Firmware Interface Table
Firmware Interface Table FIT Ordering Rules FIT Header (Type 0) Rules Microcode Update (Type 1) Rules Startup ACM (Type 2) Rules Diagnostic ACM (Type 3) Rules BIOS Startup Module (Type 7) Rules TPM Policy Record (Type 8) Rules BIOS Policy Data Record (Type 9) Rules Intel® TXT Policy Data Record (Type 0x0A) Rules Key Manifest Record (Type 0x0B) Rules Boot Policy Manifest (Type 0x0C) Rules Intel® CSE Secure Boot (Type 0x10) Rules Feature Policy Record (Type 0x2D) Rules
FIT Ordering Rules
FIT Header (Type 0) Rules
Microcode Update (Type 1) Rules
Startup ACM (Type 2) Rules
Diagnostic ACM (Type 3) Rules
BIOS Startup Module (Type 7) Rules
TPM Policy Record (Type 8) Rules
BIOS Policy Data Record (Type 9) Rules
Intel® TXT Policy Data Record (Type 0x0A) Rules
Key Manifest Record (Type 0x0B) Rules
Boot Policy Manifest (Type 0x0C) Rules
Intel® CSE Secure Boot (Type 0x10) Rules
Feature Policy Record (Type 0x2D) Rules
Legal
Firmware Interface Table Introduction
Summary of Key Requirements:
FIT Pointer
Firmware Interface Table

Startup ACM (Type 2) Rules

  1. At least one Startup ACM (Type 2) Entry in the FIT is required for FIT boot support.
  2. The address field points to a Startup ACM. Specifically, the address field in the type 2 record points to the first byte of the ACM header.
  3. Type 2 entry must point to an address that is accessible by the processor at reset vector.
  4. Internal to the processor, one MTRR base/limit pair is used to map Startup AC module. This places alignment restrictions on the Startup ACM. The MTRR size (called MTRR_​Size) must be a power of 2 and the base (MTRR_​Base) must be a multiple of MTRR size. The following equation defines MTRR_​Size.

Equation 1 .MTRR Size Calculation

MTRR_​Size = 2**(ceiling(log2( Startup_​ACM_​size )))

Note:Ceiling is a mathematical function. Ceiling(x) returns the smallest integer x larger than x

Example: If the size of Startup ACM is 13 k, MTRR_​Size is 16k (the next power of 2), and Startup ACM must be aligned on 16k boundary.

  1. ACM may be smaller than size of allocated Authenticated Code Execution Area (ACEA) computed by the above formula. ACEA completely obscures flash part at addresses occupied by itself, therefore no objects that ACM needs to reach must be located in this obscured area. This includes FIT and all objects pointed to by FIT records.
  2. The C_​V bit in this entry should be clear.
  3. The Size field is not used. BIOS should set this field to 0.
  4. The Version field should be set to 0x0100.
Diagnostic ACM (Type 3) Rules