tpm2_clearcontrol(1)

📦
version 5.8 · 10 versions
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🎀 tpm2_clearcontrol 💅

okay bestie, welcome to tpm2_clearcontrol(1) — it's a General Commands Manual situation, and this little icon is literally the bouncer for the TPM clear door 🚪✨

✨ NAME ✨

tpm2_clearcontrol(1) — sets / clears the TPMA_PERMANENT.disableClear attribute so you can effectively block or unblock the lockout authorization handle from issuing a TPM clear. it's giving "you're not on the list" energy 🫶

🌸 SYNOPSIS 🌸

tpm2_clearcontrol [OPTIONS] [ARGUMENT]

💖 DESCRIPTION 💖

So tpm2_clearcontrol(1) lets a user who knows either the lockout auth or the platform hierarchy auth set disableClear — and disableClear is the thing that stops the lockout authorization's ability to run tpm2_clear. no cap, that's the whole vibe. 🛑

The plot twist: only a user with authorization knowledge of the platform hierarchy can clear disableClear. that's the main character hierarchy, periodt 👑

By default, the tool attempts to clear the disableClear bit.

note: the platform hierarchy auth handle can always be used to clear the TPM with the tpm2_clear command. like, always. it does not care. 😭

💅 OPTIONS 💅

  • -C, --hierarchy=OBJECT — says which auth handle the tool should operate on: either the platform hierarchy or lockout. default is the platform hierarchy handle. you specify it as p|l|platform|lockout.
NOTE: operating on the platform hierarchy requires platform authentication. don't forget your keys bestie 🔑
  • -P, --auth=AUTH — the authorization value of the hierarchy you picked with -C. this tool only respects the Password and HMAC options. that's it, that's the list ✨
  • --cphash=FILE — a file path where the hash of the command parameters gets recorded. this is commonly termed as cpHash.
NOTE: when this option is selected, the tool will not actually execute the command — it simply returns a cpHash. so it's giving ✨window shopping✨ not ✨buying✨.
  • ARGUMENT — **specify an integer 0|1 or a string c|s to clear or set the disableClear attribute. ngl, this is the whole point of the tool 🎯

🔎 References 🔎

🦋 Context Object Format 🦋

The type of a context object — whether it's a handle or a file name — is determined by the following logic, in order:

  • If the argument is a file path, then the file is loaded as a restored TPM transient object.
  • If the argument is a prefix match on one of:
    • owner: the owner hierarchy
    • platform: the platform hierarchy
    • endorsement: the endorsement hierarchy
    • lockout: the lockout control persistent object
  • If the argument can be loaded as a number, it will be treated as a handle, e.g. 0x81010013, and used directly as _OBJECT_.

🌈 Authorization Formatting 🌈

Authorization for use of an object in TPM2.0 can come in 3 different forms:

  1. Password
  2. HMAC
  3. Sessions
NOTE: "Authorizations default to the EMPTY PASSWORD when not specified." so yeah, no password is still a password. iconic 💀

For authentication with auth values, the tool commands implicitly generate an HMAC session. thus passwords are not transmitted unencrypted. this does not apply to passwords defined for objects — in that case, an HMAC session should be used (see tpm2_startauthsession(1)). keeping it cute and encrypted 🔐

🍓 Passwords 🍓

Passwords are interpreted in the following forms below using prefix identifiers.

Note: by default, passwords are assumed to be in the string form when they don't have a prefix.

⭐ String ⭐

A string password, specified by prefix str: or by its absence (raw string, no prefix), is not interpreted — it's used directly for authorization.

Examples

foobar
str:foobar

🧚 Hex-string 🧚

A hex-string password, specified by prefix hex:, gets converted from hexadecimal form into a byte array form — which is literally how you get passwords with non-printable and/or terminal un-friendly characters. bestie it's giving ✨glow up✨ for weird bytes.

Example

hex:1122334455667788

🎀 File 🎀

A file based password, specified by prefix file:, should be the path of a file containing the password to be read by the tool — or a - to use stdin. storing passwords in files prevents information leakage; passwords passed as options can be read from the process list or common shell history features. lowkey important, protect your secrets 🫶

Examples

# to use stdin and be prompted
file:-

# to use a file from a path
file:path/to/password/file

# to echo a password via stdin:
echo foobar | tpm2_tool -p file:-

# to use a bash here-string via stdin:

tpm2_tool -p file:- <<< foobar

💜 Sessions 💜

When you're using a policy session to authorize the use of an object, prefix the option argument with the session keyword. then indicate a path to a session file that was created with tpm2_startauthsession(1). optionally, if the session requires an auth value to be sent with the session handle (e.g. policy password), then append a + and a string as described in the Passwords section. obsessed with the flexibility honestly 💅

Examples

To use a session context file called session.ctx:

session:session.ctx

To use a session context file called session.ctx AND send the authvalue mypassword:

session:session.ctx+mypassword

To use a session context file called session.ctx AND send the HEX authvalue 0x11223344:

session:session.ctx+hex:11223344

🌸 PCR Authorizations 🌸

You can satisfy a PCR policy using the pcr: prefix and the PCR minilanguage. the PCR minilanguage is as follows:

<pcr-spec>=<raw-pcr-file>

The PCR spec is documented in the section "PCR bank specifiers".

The raw-pcr-file is an optional argument that contains the output of the raw PCR contents as returned by tpm2_pcrread(1).

PCR bank specifiers

Examples

To satisfy a PCR policy of sha256 on banks 0, 1, 2 and 3, use a specifier of:

pcr:sha256:0,1,2,3

specifying AUTH.

👑 COMMON OPTIONS 👑

This collection of options is common to many programs and provides information that many users may expect. the group chat classics fr fr 🫶

  • -h, --help=[man|no-man] — displays the tool's manpage. by default it attempts to invoke the manpager for the tool, however, on failure it will output a short tool summary. same behavior if the man option argument is specified, but if explicit man is requested, the tool will provide errors from man on stderr. if the no-man option is specified, or the manpager fails, the short options will be output to stdout.

To successfully use the manpages feature, the manpages need to be installed or on MANPATH. see man(1) for more details. iykyk 📖

  • -v, --version — displays version information for this tool, supported tctis, and exits. cute and quick ✨
  • -V, --verbose — increases the information the tool prints to the console during its execution. when using this option, the file and line number are printed. it's giving receipts 🧾
  • -Q, --quiet — silences normal tool output to stdout. shhh 🤫
  • -Z, --enable-errata — enables the application of errata fixups. useful if an errata fixup needs to be applied to commands sent to the TPM. defining the environment variable TPM2TOOLS_ENABLE_ERRATA is equivalent. 🌈
  • -z, --pwd-session — uses a password session instead of an HMAC session for authentication. a clear text password is passed to the TPM to authorize the action. this option can be used to avoid problems when unsalted sessions are used in OpenSSL FIPS mode. if auth values are used, a salted session should be used for authentication. 🧂
  • -R, --autoflush — enables autoflush for transient objects created by the command. if a parent object is loaded from a context file, the transient parent object will also be flushed. autoflush can also be activated if the environment variable TPM2TOOLS_AUTOFLUSH is set to yes or true. information many users may expect. 🚽✨

🦋 TCTI Configuration 🦋

The TCTI, or "Transmission Interface", is the communication mechanism with the TPM. TCTIs can be changed for communication with TPMs across different mediums. it's basically the aux cord to your TPM 🔌

To control the TCTI, the tools respect:

  1. The command line option -T or --tcti
  2. The environment variable: TPM2TOOLS_TCTI.
Note: the command line option always overrides the environment variable. always always 💅

The current known TCTIs are:

  • tabrmd — the resource manager, called tabrmd. note that tabrmd and abrmd as a tcti name are synonymous.
  • mssim — typically used for communicating to the TPM software simulator.
  • device — used when talking directly to a TPM device file.
  • none — do not initialize a connection with the TPM. some tools allow for off-tpm options and thus support not using a TCTI. tools that do not support it will error when attempted to be used without a TCTI connection. does not support ANY options and MUST BE presented as the exact text of none. no notes, exact text only 😤

The arguments to either the command line option or the environment variable are in the form:

<tcti-name>:<tcti-option-config>

Specifying an empty string for either the <tcti-name> or <tcti-option-config> results in the default being used for that portion respectively. ✨defaults✨

⭐ TCTI Defaults ⭐

When a TCTI is not specified, the default TCTI is searched for using dlopen(3) semantics. the tools will search for tabrmd, device and mssim TCTIs IN THAT ORDER and USE THE FIRST ONE FOUND. so it's giving ✨first come, first served✨

You can query what TCTI will be chosen as the default by using the -v option to print the version information. the default-tcti key-value pair will indicate which of the aforementioned TCTIs is the default. 🎀

💜 Custom TCTIs 💜

Any TCTI that implements the dynamic TCTI interface can be loaded. the tools internally use dlopen(3), and the raw tcti-name value is used for the lookup. thus, this could be a path to the shared library, or a library name as understood by dlopen(3) semantics. bring your own tcti bestie 🧚

🌈 TCTI OPTIONS 🌈

This collection of options is used to configure the various known TCTI modules available:

  • device — for the device TCTI, the TPM character device file for use by the device TCTI can be specified. the default is /dev/tpm0.

Example: -T device:/dev/tpm0 or export TPM2TOOLS_TCTI="device:/dev/tpm0"

  • mssim — for the mssim TCTI, the domain name or IP address and port number used by the simulator can be specified. the default are 127.0.0.1 and 2321.

Example: -T mssim:host=localhost,port=2321 or export TPM2TOOLS_TCTI="mssim:host=localhost,port=2321"

  • abrmd — for the abrmd TCTI, the configuration string format is a series of simple key value pairs separated by a , character. each key and value string are separated by a = character.
    • TCTI abrmd supports two keys:
      1. bus_name : the name of the tabrmd service on the bus (a string).
      2. bus_type : the type of the dbus instance (a string) limited to session and system.

Specify the tabrmd tcti name and a config string of bus_name=com.example.FooBar:

\--tcti=tabrmd:bus_name=com.example.FooBar

Specify the default (abrmd) tcti and a config string of bus_type=session:

\--tcti:bus_type=session
NOTE: abrmd and tabrmd are synonymous. various known TCTI modules. 💫

🔥 EXAMPLES 🔥

Set the disableClear to block the lockout authorization's access to TPM clear

tpm2_clearcontrol -C l s

Clear the disableClear to unblock lockout authorization for TPM clear

tpm2_clearcontrol -C p c

💖 RETURNS 💖

okay so like, when the tool finishes doing its thing, it tells you how it went with a little code — and here's the whole menu of what you might get back, bestie:

  • 0 — Success! 🎉 it worked, we love that for us, main character energy fr.
  • 1 — General non-specific error. 😭 like... something went wrong but honestly? nobody's saying what. a mystery.
  • 2 — Options handling error. 🙈 you gave it flags it didn't vibe with, iykyk.
  • 3 — Authentication error. 💀 the auth didn't pass the vibe check, ngl.
  • 4 — TCTI related error. 🫶 the TCTI layer got messy, that's a whole thing (see above, you already got the lore).
  • 5 — Non supported scheme. Applicable to tpm2_testparams. 👑 that one's specifically for tpm2_testparams, not this tool, so don't come for me.

🦋 BUGS 🦋

Found a bug? not you being the detective 🔍 — hit up Github Issues. that's the whole vibe. periodt.

🌸 HELP 🌸

Need a hand? See the Mailing List. the community's got you 🫶✨

🎀 License 🎀

okay so legal moment, but make it cute — this work is licensed under the Creative Commons Attribution 4.0 International License (CC BY 4.0). 💅 iconic of them honestly.

and that's the whole page, bestie! 🧚‍♀️ you ate that. this little beauty comes to you from tpm2-tools, and yes, the page you're reading is tpm2_clearcontrol(1) — go forth and clear-control responsibly 💜🌈⭐
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