crypt_policy/
lib.rs

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1// Copyright 2024 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
5//! crypt_policy contains all the key policy logic for the different operations that can be done
6//! with hardware keys.  Keeping the policy logic in one place makes it easier to audit.
7
8use anyhow::{bail, Context, Error};
9
10#[derive(Clone, Copy, PartialEq)]
11pub enum Policy {
12    Null,
13    TeeRequired,
14    TeeTransitional,
15    TeeOpportunistic,
16}
17
18impl TryFrom<String> for Policy {
19    type Error = Error;
20
21    fn try_from(value: String) -> Result<Self, Self::Error> {
22        match value.as_ref() {
23            "null" => Ok(Policy::Null),
24            "tee" => Ok(Policy::TeeRequired),
25            "tee-transitional" => Ok(Policy::TeeTransitional),
26            "tee-opportunistic" => Ok(Policy::TeeOpportunistic),
27            p => bail!("unrecognized key source policy: '{p}'"),
28        }
29    }
30}
31
32/// Reads the policy from well-known locations in `/boot`.
33pub async fn get_policy() -> Result<Policy, Error> {
34    let policy = fuchsia_fs::file::read_in_namespace_to_string("/boot/config/zxcrypt").await;
35    let policy = match policy {
36        Ok(policy) => policy,
37        // In tests, the configuration is found in the same package as fshost.
38        Err(_) => fuchsia_fs::file::read_in_namespace_to_string("/pkg/config/zxcrypt").await?,
39    };
40    policy.try_into()
41}
42
43#[derive(Debug)]
44pub enum KeySource {
45    Null,
46    Tee,
47}
48
49/// Fxfs and zxcrypt have different null keys, so operations have to indicate which is ultimately
50/// going to consume the key we produce.
51pub enum KeyConsumer {
52    /// The null key for fxfs is a 128-bit key with the bytes "zxcrypt" at the beginning and then
53    /// padded with zeros. This is for legacy reasons - earlier versions of this code picked this
54    /// key, so we need to continue to use it to avoid wiping everyone's null-key-encrypted fxfs
55    /// data partitions.
56    Fxfs,
57    /// The null key for zxcrypt is a 256-bit key containing all zeros.
58    Zxcrypt,
59}
60
61impl KeySource {
62    pub async fn get_key(&self, consumer: KeyConsumer) -> Result<Vec<u8>, Error> {
63        match self {
64            KeySource::Null => match consumer {
65                KeyConsumer::Fxfs => {
66                    let mut key = b"zxcrypt".to_vec();
67                    key.resize(16, 0);
68                    Ok(key)
69                }
70                KeyConsumer::Zxcrypt => Ok(vec![0u8; 32]),
71            },
72            KeySource::Tee => {
73                // Regardless of the consumer of this key, the key we retrieve with kms is always
74                // named "zxcrypt". This is so that old recovery images that might not be aware of
75                // fxfs can still wipe the data keys during a factory reset.
76                kms_stateless::get_hardware_derived_key(kms_stateless::KeyInfo::new_zxcrypt())
77                    .await
78                    .context("failed to get hardware key")
79            }
80        }
81    }
82}
83
84/// Returns all valid key sources when formatting a volume, based on `policy`.
85pub fn format_sources(policy: Policy) -> Vec<KeySource> {
86    match policy {
87        Policy::Null => vec![KeySource::Null],
88        Policy::TeeRequired => vec![KeySource::Tee],
89        Policy::TeeTransitional => vec![KeySource::Tee],
90        Policy::TeeOpportunistic => vec![KeySource::Tee, KeySource::Null],
91    }
92}
93
94/// Returns all valid key sources when unsealing a volume, based on `policy`.
95pub fn unseal_sources(policy: Policy) -> Vec<KeySource> {
96    match policy {
97        Policy::Null => vec![KeySource::Null],
98        Policy::TeeRequired => vec![KeySource::Tee],
99        Policy::TeeTransitional => vec![KeySource::Tee, KeySource::Null],
100        Policy::TeeOpportunistic => vec![KeySource::Tee, KeySource::Null],
101    }
102}
crypt_policy/lib.rs

crypt_policy/
lib.rs
