Systems with TXT enabled may issue the TPM2_Startup() command from a
locality other than 0. In this case, the initial value of PCR0 will
represent the locality that the call was made from. This is exposed to
higher layers by an EV_NO_ACTION event that has data containing the
NULL-terminated string "StartupLocality" followed by a single byte
representing the state of the locality. As this event is EV_NO_ACTION,
it does not represent an extension in itself.
So:
1) Ignore events that are EV_NO_ACTION when replaying the log, except:
2) For PCR0, if an event is EV_NO_ACTION and contains the string
"StartupLocality", use the final byte of the event data as the initial
value of PCR0 for the replay.
Using the length of a digest to infer the hash algorithm is somewhat
fragile - if we end up with multiple hash algorithms that share the same
digest length, things will break. Instead, pass more complete digest
information through to relevant functions and figure things out by
mapping the TPM hash algorithm to the appropriate Golang type.
Crypto agile logs may contain digest types that we don't currently
handle. However, we still need to know how long each digest is in order
to read over the appropriate amount of the buffer. This information is
provided to us as part of the spec header - make use of it rather than
hardcoding the set of digests and lengths we know about.
@brandonweeks detected another case of the "make([]T, untrustedValue)"
pattern, which would allow an attacker to cause the parser to allocate
an unbounded amount of memory.
Fix this by reading one algorithm at a time instead of pre-allocating a
slice of algorithms.
This PR adds event log parsing logic. It's main goal is to require
validation at the same time as parsing, so structured events are always
verified against a quote. This new API replaces the exisitng "verifier"
package.
It's not a goal of this PR to parse the event data. This will be a
follow up, but since different users might want to parse different
events based on the OS, this API lets users of this package implement
custom event data parsing if they absolutely need to.
