tpm2_nvread(1)

📦
version 5.8 · 10 versions
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💾 tpm2_nvread(1) — read the data stored in a Non-Volatile (NV)s index 💅

okay bestie, welcome to the General Commands Manual entry for tpm2_nvread(1) — manual name folded right in near the top so we did not have to copy that boring header line, and honestly? slay. This tool reads the data stored in a Non-Volatile (NV)s index, and it has a whole stack of options for doing it exactly right.

✨ NAME ✨

tpm2_nvread(1) — Read the data stored in a Non-Volatile (NV)s index.

🛠️ SYNOPSIS 🛠️

tpm2_nvread [OPTIONS] [ARGUMENT]

💬 DESCRIPTION 💬

tpm2_nvread(1) — Read the data stored in a Non-Volatile (NV)s index. The index can be specified as a raw handle or as an offset value to the nv handle range TPM2_HR_NV_INDEX. So you can point at it directly or by offset, iykyk.

🎀 OPTIONS 🎀

  • -C, --hierarchy=OBJECT — says which hierarchy is used to authorize. The supported options are:
    • o for TPM_RH_OWNER
    • p for TPM_RH_PLATFORM
    • <num> where a hierarchy handle or nv-index may be used.

When -C isn’t explicitly passed, the index handle will be used to authorize against the index. The index auth value is set via the -p option to tpm2_nvdefine(1).

  • -o, --output=FILE — File to write data 💾.
  • -P, --auth=AUTH — Specifies the authorization value for the hierarchy 🔐.
  • -s, --size=NATURAL_NUMBER — Specifies the size of data to be read in bytes, starting from 0 if offset is not specified. If not specified, the size of the data as reported by the public portion of the index will be used.
  • --offset=NATURAL_NUMBER — The offset within the NV index to start reading from.
  • --cphash=FILE — File path to record the hash of the command parameters. 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, unless rphash is also required.
  • --rphash=FILE — File path to record the hash of the response parameters. This is commonly termed as rpHash.
  • -n, --name=FILE — The name of the NV index that must be provided when only calculating the cpHash without actually dispatching the command to the TPM.
  • -S, --session=FILE — The session created using tpm2_startauthsession. This can be used to specify an auxiliary session for auditing and or encryption/decryption of the parameters.
  • --print-yaml — Output the content of the NV index in a human readable format, useful for displaying the content of counter, bits and extend and pin indices. When this argument is provided size and offset is ignored.
  • ARGUMENT — the command line argument specifies the NV index or offset number.

📚 References 📚

the reference-y goodies start here, bestie:

🧸 Context Object Format 🧸

The type of a context object, whether it is a handle or file name, is determined according to 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 argument can be loaded as a number it will be treat as a handle, e.g. 0x81010013 and used directly._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”.

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 this case, an HMAC session should be used (see tpm2_startauthsession(1)).

🔑 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 do not have a prefix.

🧵 String 🧵

A string password, specified by prefix str: or it’s absence (raw string without prefix) is not interpreted, and is directly used for authorization.

Examples:

foobar
str:foobar

🧪 Hex-string 🧪

A hex-string password, specified by prefix hex: is converted from a hexidecimal form into a byte array form, thus allowing passwords with non-printable and/or terminal un-friendly characters.

Example:

hex:1122334455667788

📁 File 📁

A file based password, specified be 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.

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 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 (eg policy password), then append a + and a string as described in the Passwords section.

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 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 are common to many programs and provide information that many users may expect.

  • -h, --help=[man|no-man] — Display the tools manpage. By default, it attempts to invoke the manpager for the tool, however, on failure will output a short tool summary. This is the same behavior if the “man” option argument is specified, however if explicit “man” is requested, the tool will provide errors from man on stderr. If the “no-man” option if specified, or the manpager fails, the short options will be output to stdout. To successfully use the manpages feature requires the manpages to be installed or on MANPATH, See man(1) for more details.
  • -v, --version — Display version information for this tool, supported tctis and exit.
  • -V, --verbose — Increase the information that the tool prints to the console during its execution. When using this option the file and line number are printed.
  • -Q, --quiet — Silence normal tool output to stdout.
  • -Z, --enable-errata — Enable the application of errata fixups. Useful if an errata fixup needs to be applied to commands sent to the TPM. Defining the environment TPM2TOOLS_ENABLE_ERRATA is equivalent.
  • -z, --pwd-session — Use password session instead of a 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 — Enable autoflush for transient objects created by the command. If a parent object is loaded from a context file also the transient parent object will be flushed. Autoflush can also be activated if the environment variable TPM2TOOLS_AUTOFLUSH is 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.

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.

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 initalize 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”.

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.

🧸 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. 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.

✨ TCTI OPTIONS ✨

Okay so this little crew of options is all about setting up the various known TCTI modules that are available — think of them as the different ways your tooling can actually talk to the TPM 💅

  • device — for the device TCTI, you can specify the TPM character device file it should use. The default is /dev/tpm0.

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

  • mssim — for the mssim TCTI, you can specify the domain name or IP address and the port number that the simulator uses. The defaults 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.
    • The 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. the various known TCTI modules.d)

🌸 EXAMPLES 🌸

🎀 Read 32 bytes from an index starting at offset 0

Bestie, this is the whole lil journey — define it, write to it, read it back, slay ✨

tpm2_nvdefine -C o -s 32 -a "ownerread|policywrite|ownerwrite" 1

echo "please123abc" > nv.dat

tpm2_nvwrite -C o -i nv.dat 1

tpm2_nvread -C o -s 32 1

💀 Returns 💀

Tools can return any of the following codes, no cap:

  • 0 — Success. we love to see it 👑
  • 1 — General non-specific error.
  • 2 — Options handling error.
  • 3 — Authentication error.
  • 4 — TCTI related error.
  • 5 — Non supported scheme. Applicable to tpm2_testparams.

🦋 BUGS 🦋

Github Issues — that's the spot, go yell there (lovingly) 🫶

🧚 HELP 🧚

See the Mailing List — the community is right there if you're stuck, fr fr 💖

⭐ License ⭐

This work is licensed under the Creative Commons Attribution 4.0 International License (CC BY 4.0).

and that's the whole page, bestie — you ate that 💅✨ This one comes from the tpm2-tools source, version-and-date footer and all, and it's dated for page tpm2_nvread(1). Go forth and read those NV bytes, icon 🎀💜

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