kms_stateless/
lib.rs

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1// Copyright 2022 The Fuchsia Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5use fuchsia_async::TimeoutExt as _;
6use futures::{TryFutureExt as _, TryStreamExt as _};
7use std::ffi::{CStr, CString};
8
9/// Hardware derived key is expected to be a 128-bit AES key.
10const DERIVED_KEY_SIZE: usize = 16;
11const KEY_INFO_SIZE: usize = 32;
12
13#[derive(Copy, Clone, Debug)]
14pub enum TaKeysafeCommand {
15    GetUserDataStorageKey = 8,
16    RotateHardwareDerivedKey = 9,
17}
18
19/// Error values generated by this library
20#[derive(Debug, thiserror::Error)]
21pub enum Error {
22    #[error("tee command {0:?} failed: {1}")]
23    TeeCommand(TaKeysafeCommand, u32),
24    #[error("tee command {0:?} failed: not supported")]
25    TeeCommandNotSupported(TaKeysafeCommand),
26    #[error(
27        "tee command {:?} failed: buffer with hardcoded size {} bytes was too small",
28        .0,
29        DERIVED_KEY_SIZE,
30    )]
31    TeeCommandBufferTooSmall(TaKeysafeCommand),
32    #[error("failed to open dev directory")]
33    DevDirectoryOpen(#[from] fuchsia_fs::node::OpenError),
34    #[error("timeout waiting for tee device")]
35    TeeDeviceWaitTimeout,
36    #[error("failure waiting for tee device")]
37    TeeDeviceWaitFailure(#[from] anyhow::Error),
38}
39
40/// The info used to identify a key.
41pub struct KeyInfo {
42    info: [u8; KEY_INFO_SIZE],
43}
44
45impl KeyInfo {
46    /// Creates a new key info buffer using the provided string as the identifier.
47    pub fn new(info: impl ToString) -> Self {
48        Self::new_bytes(info.to_string().as_bytes())
49    }
50
51    /// Creates a new key info buffer using "zxcrypt" as the identifier.
52    pub fn new_zxcrypt() -> Self {
53        Self::new_bytes("zxcrypt".as_bytes())
54    }
55
56    fn new_bytes(info_bytes: &[u8]) -> Self {
57        let mut info = [0; KEY_INFO_SIZE];
58        // This will panic if the provided info is longer than 32 bytes, which is fine because
59        // that's a programming error.
60        info[..info_bytes.len()].copy_from_slice(info_bytes);
61        Self { info }
62    }
63}
64
65fn call_command(
66    device: Option<&CStr>,
67    op: &mut tee::TeecOperation,
68    id: TaKeysafeCommand,
69) -> Result<(), Error> {
70    match device {
71        Some(dev) => tee::call_command_on_device(dev, op, id as u32),
72        None => tee::call_command(op, id as u32),
73    }
74    .map_err(|e| match e {
75        tee::TEEC_ERROR_NOT_SUPPORTED => Error::TeeCommandNotSupported(id),
76        tee::TEEC_ERROR_SHORT_BUFFER => Error::TeeCommandBufferTooSmall(id),
77        e => Error::TeeCommand(id, e),
78    })
79}
80
81fn get_key_from_tee_device(device: Option<&CStr>, info: KeyInfo) -> Result<Vec<u8>, Error> {
82    let mut key_buf = [0u8; DERIVED_KEY_SIZE];
83
84    let mut op = tee::create_operation(
85        tee::teec_param_types(
86            tee::TEEC_MEMREF_TEMP_INPUT,
87            tee::TEEC_NONE,
88            tee::TEEC_NONE,
89            tee::TEEC_MEMREF_TEMP_OUTPUT,
90        ),
91        [
92            tee::get_memref_input_parameter(&info.info),
93            tee::get_zero_parameter(),
94            tee::get_zero_parameter(),
95            tee::get_memref_output_parameter(&mut key_buf),
96        ],
97    );
98
99    call_command(device, &mut op, TaKeysafeCommand::GetUserDataStorageKey)?;
100
101    Ok(key_buf.to_vec())
102}
103
104fn rotate_key_from_tee_device(device: Option<&CStr>, info: KeyInfo) -> Result<(), Error> {
105    let mut op = tee::create_operation(
106        tee::teec_param_types(
107            tee::TEEC_MEMREF_TEMP_INPUT,
108            tee::TEEC_NONE,
109            tee::TEEC_NONE,
110            tee::TEEC_NONE,
111        ),
112        [
113            tee::get_memref_input_parameter(&info.info),
114            tee::get_zero_parameter(),
115            tee::get_zero_parameter(),
116            tee::get_zero_parameter(),
117        ],
118    );
119
120    call_command(device, &mut op, TaKeysafeCommand::RotateHardwareDerivedKey)
121}
122
123/// Gets a hardware derived key using the first device found in /dev/class/tee.
124/// This is useful in early boot when other services may not be up.
125pub async fn get_hardware_derived_key(info: KeyInfo) -> Result<Vec<u8>, Error> {
126    const DEV_CLASS_TEE: &str = "/dev/class/tee";
127
128    let dir = fuchsia_fs::directory::open_in_namespace(DEV_CLASS_TEE, fuchsia_fs::Flags::empty())?;
129    let mut stream = device_watcher::watch_for_files(&dir).await?;
130    let first = stream
131        .try_next()
132        .map_err(Error::from)
133        .on_timeout(std::time::Duration::from_secs(5), || Err(Error::TeeDeviceWaitTimeout))
134        .await?;
135    let first = first.ok_or_else(|| {
136        Error::TeeDeviceWaitFailure(anyhow::anyhow!(
137            "'{DEV_CLASS_TEE}' watcher closed unexpectedly"
138        ))
139    })?;
140    let first = first.to_str().expect("paths are utf-8");
141
142    let dev = format!("{DEV_CLASS_TEE}/{first}");
143    let dev = CString::new(dev).expect("paths do not contain nul bytes");
144    get_key_from_tee_device(Some(&dev), info)
145}
146
147/// Gets a hardware derived key using the service fuchsia.tee.Application. This should be used from
148/// components.
149pub async fn get_hardware_derived_key_from_service(info: KeyInfo) -> Result<Vec<u8>, Error> {
150    get_key_from_tee_device(None, info)
151}
152
153/// Rotates the hardware derived key from a tee device at the /dev/class/tee.
154/// This is useful in early boot when other services may not be up.
155pub async fn rotate_hardware_derived_key(info: KeyInfo) -> Result<(), Error> {
156    const DEV_CLASS_TEE: &str = "/dev/class/tee";
157
158    let dir = fuchsia_fs::directory::open_in_namespace(DEV_CLASS_TEE, fuchsia_fs::Flags::empty())?;
159    let mut stream = device_watcher::watch_for_files(&dir).await?;
160    let first = stream
161        .try_next()
162        .map_err(Error::from)
163        .on_timeout(std::time::Duration::from_secs(5), || Err(Error::TeeDeviceWaitTimeout))
164        .await?;
165    let first = first.ok_or_else(|| {
166        Error::TeeDeviceWaitFailure(anyhow::anyhow!(
167            "'{DEV_CLASS_TEE}' watcher closed unexpectedly"
168        ))
169    })?;
170    let first = first.to_str().expect("paths are utf-8");
171
172    let dev = format!("{DEV_CLASS_TEE}/{first}");
173    let dev = CString::new(dev).expect("paths do not contain nul bytes");
174    rotate_key_from_tee_device(Some(&dev), info)
175}
176
177/// Rotates an existing hardware derived key identified by [`info`] using the service
178/// fuchsia.tee.Application. This should be used from components.
179pub async fn rotate_hardware_derived_key_from_service(info: KeyInfo) -> Result<(), Error> {
180    rotate_key_from_tee_device(None, info)
181}
kms_stateless/lib.rs

kms_stateless/
lib.rs
