Kyle Isom
115f23a3ea
Vendor dependencies and expose control program binaries via nix build. Uses nixpkgs-unstable for Go 1.26 support. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
56 lines
2.0 KiB
Go
56 lines
2.0 KiB
Go
package tpm2
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// pcrSelectionFormatter is a Platform TPM Profile-specific interface for
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// formatting TPM PCR selections.
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// This interface isn't (yet) part of the go-tpm public interface. After we
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// add a second implementation, we should consider making it public.
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type pcrSelectionFormatter interface {
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// PCRs returns the TPM PCR selection bitmask associated with the given PCR indices.
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PCRs(pcrs ...uint) []byte
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}
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// PCClientCompatible is a pcrSelectionFormatter that formats PCR selections
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// suitable for use in PC Client PTP-compatible TPMs (the vast majority):
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// https://trustedcomputinggroup.org/resource/pc-client-platform-tpm-profile-ptp-specification/
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// PC Client mandates at least 24 PCRs but does not provide an upper limit.
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var PCClientCompatible pcrSelectionFormatter = pcClient{}
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type pcClient struct{}
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// The TPM requires all PCR selections to be at least big enough to select all
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// the PCRs in the minimum PCR allocation.
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const pcClientMinimumPCRCount = 24
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func (pcClient) PCRs(pcrs ...uint) []byte {
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// Find the biggest PCR we selected.
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maxPCR := uint(0)
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for _, pcr := range pcrs {
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if pcr > maxPCR {
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maxPCR = pcr
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}
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}
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selectionSize := maxPCR/8 + 1
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// Enforce the minimum PCR selection size.
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if selectionSize < (pcClientMinimumPCRCount / 8) {
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selectionSize = (pcClientMinimumPCRCount / 8)
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}
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// Allocate a byte array to store the bitfield, that has at least
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// enough bits to store our selections.
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selection := make([]byte, selectionSize)
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for _, pcr := range pcrs {
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// The PCR selection mask is byte-wise little-endian:
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// select[0] contains bits representing the selection of PCRs 0 through 7
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// select[1] contains PCRs 8 through 15, and so on.
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byteIdx := pcr / 8
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// Within the byte, the PCR selection is bit-wise big-endian:
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// bit 0 of select[0] contains the selection of PCR 0
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// bit 1 of select[0] contains the selection of PCR 1, and so on.
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bitIdx := pcr % 8
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selection[byteIdx] |= (1 << bitIdx)
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}
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return selection
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}
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