avmd/src/avmd.rs

// Copyright 2022, The Android Open Source Project
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

extern crate alloc;

use alloc::{
    string::{String, ToString},
    vec::Vec,
};
use apkverify::SignatureAlgorithmID;
use core::fmt;
use serde::{Deserialize, Serialize};

/// An Avmd struct contains
/// - A header with version information that allows rollback when needed.
/// - A list of descriptors that describe different images.
#[derive(Serialize, Deserialize, Debug, Clone)]
pub struct Avmd {
    header: Header,
    descriptors: Vec<Descriptor>,
}

impl fmt::Display for Avmd {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        writeln!(f, "Descriptors:")?;
        for descriptor in &self.descriptors {
            write!(f, "{}", descriptor)?;
        }
        Ok(())
    }
}

impl Avmd {
    /// Creates an instance of Avmd with a given list of descriptors.
    pub fn new(descriptors: Vec<Descriptor>) -> Avmd {
        Avmd { header: Header::default(), descriptors }
    }
}

static AVMD_MAGIC: u32 = 0x444d5641;
static AVMD_VERSION_MAJOR: u16 = 1;
static AVMD_VERSION_MINOR: u16 = 0;

/// Header information for AVMD.
#[derive(Serialize, Deserialize, Debug, Clone)]
struct Header {
    magic: u32,
    version_major: u16,
    version_minor: u16,
}

impl Default for Header {
    fn default() -> Self {
        Header {
            magic: AVMD_MAGIC,
            version_major: AVMD_VERSION_MAJOR,
            version_minor: AVMD_VERSION_MINOR,
        }
    }
}

/// AVMD descriptor.
#[derive(Serialize, Deserialize, Debug, Clone)]
pub enum Descriptor {
    /// Descriptor type for the VBMeta images.
    VbMeta(VbMetaDescriptor),
    /// Descriptor type for APK.
    Apk(ApkDescriptor),
}

impl fmt::Display for Descriptor {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match self {
            Descriptor::VbMeta(descriptor) => write!(f, "{}", descriptor),
            Descriptor::Apk(descriptor) => write!(f, "{}", descriptor),
        }
    }
}

/// VbMeta descriptor.
#[derive(Serialize, Deserialize, Debug, Clone)]
pub struct VbMetaDescriptor {
    /// The identifier of this resource.
    #[serde(flatten)]
    pub resource: ResourceIdentifier,
    /// The SHA-512 [VBMeta digest][] calculated from the top-level VBMeta image.
    ///
    /// [VBMeta digest]: https://android.googlesource.com/platform/external/avb/+/master/README.md#the-vbmeta-digest
    pub vbmeta_digest: Vec<u8>,
}

impl fmt::Display for VbMetaDescriptor {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        writeln!(f, "  VBMeta descriptor:")?;
        writeln!(f, "    namespace:             {}", self.resource.namespace)?;
        writeln!(f, "    name:                  {}", self.resource.name)?;
        writeln!(f, "    vbmeta digest:         {}", hex::encode(&self.vbmeta_digest))?;
        Ok(())
    }
}

/// APK descriptor.
#[derive(Serialize, Deserialize, Debug, Clone)]
pub struct ApkDescriptor {
    /// The identifier of this resource.
    #[serde(flatten)]
    pub resource: ResourceIdentifier,
    /// The ID of the algoithm used to sign the APK.
    /// It should be one of the algorithms in the [list][].
    ///
    /// [list]: https://source.android.com/security/apksigning/v2#signature-algorithm-ids
    pub signature_algorithm_id: SignatureAlgorithmID,
    /// Digest of the APK's v3 signing block. TODO: fix
    pub apk_digest: Vec<u8>,
}

impl fmt::Display for ApkDescriptor {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        writeln!(f, "  APK descriptor:")?;
        writeln!(f, "    namespace:             {}", self.resource.namespace)?;
        writeln!(f, "    name:                  {}", self.resource.name)?;
        writeln!(f, "    Signing algorithm ID:  {:#04x}", self.signature_algorithm_id.to_u32())?;
        writeln!(f, "    APK digest:            {}", hex::encode(&self.apk_digest))?;
        Ok(())
    }
}

/// Resource identifier regroups information to identify resources.
#[derive(Serialize, Deserialize, Debug, Clone)]
pub struct ResourceIdentifier {
    /// Namespace of the resource.
    namespace: String,
    /// Name of the resource.
    name: String,
}

impl ResourceIdentifier {
    /// Creates an instance of ResourceIdentifier with the given
    /// namespace and name.
    pub fn new(namespace: &str, name: &str) -> ResourceIdentifier {
        ResourceIdentifier { namespace: namespace.to_string(), name: name.to_string() }
    }
}