58 lines
1.6 KiB
Markdown
58 lines
1.6 KiB
Markdown
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# Intel Authenticated Code Modules
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The Authenticated Code Modules (ACMs) are Intel digitally signed modules
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that contain code to be run before the traditional x86 CPU reset vector.
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The ACMs can be invoked at runtime through the GETSEC instruction, too.
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A platform that wants to use Intel TXT must use two ACMs:
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1. BIOS ACM
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* The BIOS ACM must be present in the boot flash.
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* The BIOS ACM must be referenced by the [FIT].
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2. SINIT ACM
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* The SINIT ACM isn't referenced by the [FIT].
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* The SINIT ACM should be provided by the boot firmware, but bootloaders
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like [TBOOT] are able to load them from the filesystem as well.
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## Retrieving ACMs
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The ACMs can be downloaded on Intel's website:
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[Intel Trusted Execution Technology](https://software.intel.com/en-us/articles/intel-trusted-execution-technology)
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If you want to extract the BLOB from vendor firmware you can search for the
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string ``LCP_POLICY_DATA`` or ``TXT``.
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## Header
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Every ACM has a fixed size header:
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```c
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/*
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* ACM Header v0.0 without dynamic part
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* Chapter A.1
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* Intel TXT Software Development Guide (Document: 315168-015)
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*/
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struct acm_header_v0 {
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uint16_t module_type;
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uint16_t module_sub_type;
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uint32_t header_len;
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uint16_t header_version[2];
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uint16_t chipset_id;
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uint16_t flags;
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uint32_t module_vendor;
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uint32_t date;
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uint32_t size;
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uint16_t txt_svn;
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uint16_t se_svn;
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uint32_t code_control;
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uint32_t error_entry_point;
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uint32_t gdt_limit;
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uint32_t gdt_ptr;
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uint32_t seg_sel;
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uint32_t entry_point;
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uint8_t reserved2[63];
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} __packed;
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```
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[FIT]: ../../soc/intel/fit.md
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[TBOOT]: https://sourceforge.net/p/tboot/wiki/Home/
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