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Diffstat (limited to 'Documentation/security/intel/txt_ibb.md')
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diff --git a/Documentation/security/intel/txt_ibb.md b/Documentation/security/intel/txt_ibb.md new file mode 100644 index 000000000000..56cee8dca5dc --- /dev/null +++ b/Documentation/security/intel/txt_ibb.md @@ -0,0 +1,39 @@ +# Intel TXT Initial Boot Block + +The Initial Boot Block (IBB) consists out of one or more files in the CBFS. + +## Constraints + +The IBB must follow the following constrains: +* One IBB must contain the reset vector as well as the [FIT table]. +* The IBB should be as small as possible. +* The IBBs must not overlap each other. +* The IBB might overlap with microcode. +* The IBB must not overlap the BIOS ACM. +* The IBB size must be a multiple of 16. +* Either one of the following: + * The IBB must be able to train the main system memory and clear all secrets. + * If the IBB cannot train the main system memory it must verify the code + that can train the main system memory and is able to clear all secrets. + +## Identification + +To add the IBBs to the [FIT], all CBFS files are added using the `cbfstool` +with the `--ibb` flag set. +The flags sets the CBFS file attribute tag to LE `' IBB'`. + +The make system in turn adds all those files to the [FIT] as type 7. + +## Intel TXT measurements + +Each IBB is measured and extended into PCR0 by [Intel TXT], before the CPU +reset vector is executed. +The IBBs are measured in the order they are listed in the [FIT]. + +## FIT schematic + +![][fit_ibb] + +[fit_ibb]: fit_ibb.svg +[FIT]: ../../soc/intel/fit.md +[Intel TXT]: txt.md |