Introduce helper for formatting PCR selection bitmasks #345
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This change introduces PCClientCompatible.PCRs(), a function that converts a variadic list of PCR indices (as ints) into a PCR selection bitmask. Because of the vagaries of TPM: 1. That the minimum size of a PCR selection bitmask is not 0, but related to the minimum number of PCRs specified by the profile 2. That the PC Client Platform TPM Profile specification mandates a minimum but not a maximum number of implementation PCR, this change creates an interface that could be implemented for other TPM profiles that specify different amounts of PCRs. The vast majority of on-market TPMs will just work with PCClientCompatible.PCRs, even if they implement more than 24 PCRs. PCRs() can panic if given invalid values; this is to allow it to be inlined into the definition of a structure that needs a PCR selection.
alexmwu
approved these changes
Sep 14, 2023
tpm2/pcrs.go
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| selection := make([]byte, selectionSize) | ||
| for _, pcr := range pcrs { | ||
| // Panic if negative PCRs are selected. | ||
| if pcr < 0 { |
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Done. I had initially used int since functions like len return int but I think uint is way better (no panics now)!
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This change introduces PCClientCompatible.PCRs(), a function that converts a variadic list of PCR indices (as ints) into a PCR selection bitmask. Because of the vagaries of TPM:
this change creates an interface that could be implemented for other TPM profiles that specify different amounts of PCRs. The vast majority of on-market TPMs will just work with PCClientCompatible.PCRs, even if they implement more than 24 PCRs.
PCRs() can panic if given invalid values; this is to allow it to be inlined into the definition of a structure that needs a PCR selection.