xref: /aosp_15_r20/system/keymint/ta/src/rkp.rs (revision 9860b7637a5f185913c70aa0caabe3ecb78441e4)

// 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.

//! Functionality for remote key provisioning

use super::KeyMintTa;
use crate::coset::{
    cbor::value::Value, iana, AsCborValue, CborSerializable, CoseKey, CoseMac0, CoseMac0Builder,
    HeaderBuilder, Label,
};
use crate::RpcInfo;
use alloc::string::{String, ToString};
use alloc::{vec, vec::Vec};
use kmr_common::crypto::{
    ec::{CoseKeyPurpose, RKP_TEST_KEY_CBOR_MARKER},
    hmac_sha256, KeyMaterial,
};
use kmr_common::{keyblob, km_err, rpc_err, try_to_vec, Error, FallibleAllocExt};
use kmr_wire::{
    cbor,
    cbor::cbor,
    keymint::{
        Algorithm, Digest, EcCurve, KeyParam, KeyPurpose, SecurityLevel, VerifiedBootState,
        UNDEFINED_NOT_AFTER, UNDEFINED_NOT_BEFORE,
    },
    read_to_value, rpc,
    rpc::{
        DeviceInfo, EekCurve, HardwareInfo, MacedPublicKey, ProtectedData,
        MINIMUM_SUPPORTED_KEYS_IN_CSR,
    },
    rpc::{AUTH_REQ_SCHEMA_V1, CERT_TYPE_KEYMINT, IRPC_V2, IRPC_V3},
    types::KeySizeInBits,
    CborError,
};

const RPC_P256_KEYGEN_PARAMS: [KeyParam; 8] = [
    KeyParam::Purpose(KeyPurpose::AttestKey),
    KeyParam::Algorithm(Algorithm::Ec),
    KeyParam::KeySize(KeySizeInBits(256)),
    KeyParam::EcCurve(EcCurve::P256),
    KeyParam::NoAuthRequired,
    KeyParam::Digest(Digest::Sha256),
    KeyParam::CertificateNotBefore(UNDEFINED_NOT_BEFORE),
    KeyParam::CertificateNotAfter(UNDEFINED_NOT_AFTER),
];

const MAX_CHALLENGE_SIZE_V2: usize = 64;

impl KeyMintTa {
    /// Return the UDS certs for the device, encoded in CBOR as per `AdditionalDKSignatures`
    /// structure in ProtectedData.aidl for IRPC HAL version 2 and as per `UdsCerts` structure in
    /// IRPC HAL version 3.
    pub fn uds_certs(&self) -> Result<Vec<u8>, Error> {
        let dice_info =
            self.get_dice_info().ok_or_else(|| rpc_err!(Failed, "DICE info not available."))?;
        try_to_vec(&dice_info.pub_dice_artifacts.uds_certs)
    }

    /// Return the CBOR-encoded `DeviceInfo`.
    pub fn rpc_device_info(&self) -> Result<Vec<u8>, Error> {
        let info = self.rpc_device_info_cbor()?;
        serialize_cbor(&info)
    }

    fn rpc_device_info_cbor(&self) -> Result<Value, Error> {
        // First make sure all the relevant info is available.
        let ids = self.get_attestation_ids().ok_or_else(|| {
            km_err!(AttestationIdsNotProvisioned, "attestation ID info not available")
        })?;
        let boot_info = self
            .boot_info
            .as_ref()
            .ok_or_else(|| km_err!(HardwareNotYetAvailable, "boot info not available"))?;
        let hal_info = self
            .hal_info
            .as_ref()
            .ok_or_else(|| km_err!(HardwareNotYetAvailable, "HAL info not available"))?;

        let brand = String::from_utf8_lossy(&ids.brand);
        let manufacturer = String::from_utf8_lossy(&ids.manufacturer);
        let product = String::from_utf8_lossy(&ids.product);
        let model = String::from_utf8_lossy(&ids.model);
        let device = String::from_utf8_lossy(&ids.device);

        let bootloader_state = if boot_info.device_boot_locked { "locked" } else { "unlocked" };
        let vbmeta_digest = cbor::value::Value::Bytes(try_to_vec(&boot_info.verified_boot_hash)?);
        let vb_state = match boot_info.verified_boot_state {
            VerifiedBootState::Verified => "green",
            VerifiedBootState::SelfSigned => "yellow",
            VerifiedBootState::Unverified => "orange",
            VerifiedBootState::Failed => "red",
        };
        let security_level = match self.hw_info.security_level {
            SecurityLevel::TrustedEnvironment => "tee",
            SecurityLevel::Strongbox => "strongbox",
            l => {
                return Err(km_err!(
                    HardwareTypeUnavailable,
                    "security level {:?} not supported",
                    l
                ))
            }
        };

        let fused = match &self.rpc_info {
            RpcInfo::V2(rpc_info_v2) => rpc_info_v2.fused,
            RpcInfo::V3(rpc_info_v3) => rpc_info_v3.fused,
        };
        // The DeviceInfo.aidl file specifies that map keys should be ordered according
        // to RFC 7049 canonicalization rules, which are:
        // - shorter-encoded key < longer-encoded key
        // - lexicographic comparison for same-length keys
        // Note that this is *different* than the ordering required in RFC 8949 s4.2.1.
        let info = cbor!({
            "brand" => brand,
            "fused" => i32::from(fused),
            "model" => model,
            "device" => device,
            "product" => product,
            "vb_state" => vb_state,
            "os_version" => hal_info.os_version.to_string(),
            "manufacturer" => manufacturer,
            "vbmeta_digest" => vbmeta_digest,
            "security_level" => security_level,
            "boot_patch_level" => boot_info.boot_patchlevel,
            "bootloader_state" => bootloader_state,
            "system_patch_level" => hal_info.os_patchlevel,
            "vendor_patch_level" => hal_info.vendor_patchlevel,
        })?;
        Ok(info)
    }

    pub(crate) fn get_rpc_hardware_info(&self) -> Result<HardwareInfo, Error> {
        match &self.rpc_info {
            RpcInfo::V2(rpc_info_v2) => Ok(HardwareInfo {
                version_number: IRPC_V2,
                rpc_author_name: rpc_info_v2.author_name.to_string(),
                supported_eek_curve: rpc_info_v2.supported_eek_curve,
                unique_id: Some(rpc_info_v2.unique_id.to_string()),
                supported_num_keys_in_csr: MINIMUM_SUPPORTED_KEYS_IN_CSR,
            }),
            RpcInfo::V3(rpc_info_v3) => Ok(HardwareInfo {
                version_number: IRPC_V3,
                rpc_author_name: rpc_info_v3.author_name.to_string(),
                supported_eek_curve: EekCurve::None,
                unique_id: Some(rpc_info_v3.unique_id.to_string()),
                supported_num_keys_in_csr: rpc_info_v3.supported_num_of_keys_in_csr,
            }),
        }
    }

    pub(crate) fn generate_ecdsa_p256_keypair(
        &mut self,
        test_mode: rpc::TestMode,
    ) -> Result<(MacedPublicKey, Vec<u8>), Error> {
        if self.rpc_info.get_version() > IRPC_V2 && test_mode == rpc::TestMode(true) {
            return Err(rpc_err!(
                Removed,
                "generate_ecdsa_p256_keypair does not support test mode in IRPC V3+ HAL."
            ));
        }

        let (key_material, chars) = self.generate_key_material(&RPC_P256_KEYGEN_PARAMS)?;

        let pub_cose_key = match key_material {
            KeyMaterial::Ec(curve, curve_type, ref key) => key.public_cose_key(
                &*self.imp.ec,
                curve,
                curve_type,
                CoseKeyPurpose::Sign,
                None,
                test_mode,
            )?,
            _ => return Err(km_err!(InvalidKeyBlob, "expected key material of type variant EC.")),
        };
        let pub_cose_key_encoded = pub_cose_key.to_vec().map_err(CborError::from)?;
        let maced_pub_key =
            build_maced_pub_key(pub_cose_key_encoded, |data| -> Result<Vec<u8>, Error> {
                // In test mode, use an all-zero HMAC key.
                if test_mode == rpc::TestMode(true) {
                    return hmac_sha256(&*self.imp.hmac, &[0; 32], data);
                }
                self.dev.rpc.compute_hmac_sha256(&*self.imp.hmac, &*self.imp.hkdf, data)
            })?;

        let key_result = self.finish_keyblob_creation(
            &RPC_P256_KEYGEN_PARAMS,
            None,
            chars,
            key_material,
            keyblob::SlotPurpose::KeyGeneration,
        )?;

        Ok((MacedPublicKey { maced_key: maced_pub_key }, key_result.key_blob))
    }

    pub(crate) fn generate_cert_req(
        &self,
        _test_mode: rpc::TestMode,
        _keys_to_sign: Vec<MacedPublicKey>,
        _eek_chain: &[u8],
        _challenge: &[u8],
    ) -> Result<(DeviceInfo, ProtectedData, Vec<u8>), Error> {
        if self.rpc_info.get_version() > IRPC_V2 {
            return Err(rpc_err!(Removed, "generate_cert_req is not supported in IRPC V3+ HAL."));
        }
        let _device_info = self.rpc_device_info()?;
        Err(km_err!(Unimplemented, "GenerateCertificateRequest is only required for RKP before v3"))
    }

    pub(crate) fn generate_cert_req_v2(
        &self,
        keys_to_sign: Vec<MacedPublicKey>,
        challenge: &[u8],
    ) -> Result<Vec<u8>, Error> {
        if self.rpc_info.get_version() < IRPC_V3 {
            return Err(km_err!(
                Unimplemented,
                "generate_cert_req_v2 is not implemented for IRPC HAL V2 and below."
            ));
        }
        if challenge.len() > MAX_CHALLENGE_SIZE_V2 {
            return Err(km_err!(
                InvalidArgument,
                "Challenge is too big. Actual: {:?}. Maximum: {:?}.",
                challenge.len(),
                MAX_CHALLENGE_SIZE_V2
            ));
        }
        // Validate mac and extract the public keys to sign from the MacedPublicKeys
        let mut pub_cose_keys: Vec<Value> = Vec::new();
        for key_to_sign in keys_to_sign {
            let maced_pub_key = key_to_sign.maced_key;
            let cose_mac0 = CoseMac0::from_slice(&maced_pub_key).map_err(CborError::from)?;
            // Decode the public cose key from payload and check for test keys in production.
            // TODO: if implementing IRPC V2, create a helper function to check for test keys that
            // takes an indication of whether test mode is allowed
            if let Some(pub_cose_key_data) = &cose_mac0.payload {
                let pub_cose_key_cbor = read_to_value(pub_cose_key_data)?;
                let pub_cose_key =
                    CoseKey::from_cbor_value(pub_cose_key_cbor.clone()).map_err(CborError::from)?;
                let params = pub_cose_key.params;
                for param in params {
                    if param.0 == Label::Int(RKP_TEST_KEY_CBOR_MARKER) {
                        return Err(rpc_err!(
                            TestKeyInProductionRequest,
                            "test key found in the request for generating CSR IRPC V3"
                        ));
                    }
                }
                pub_cose_keys.try_push(pub_cose_key_cbor)?;
            } else {
                return Err(rpc_err!(Failed, "no payload found in a MacedPublicKey"));
            }

            cose_mac0.verify_tag(&[], |expected_tag, data| -> Result<(), Error> {
                let computed_tag =
                    self.dev.rpc.compute_hmac_sha256(&*self.imp.hmac, &*self.imp.hkdf, data)?;
                if self.imp.compare.eq(expected_tag, &computed_tag) {
                    Ok(())
                } else {
                    Err(rpc_err!(InvalidMac, "invalid tag found in a MacedPublicKey"))
                }
            })?;
        }
        // Construct the `CsrPayload`
        let rpc_device_info = self.rpc_device_info_cbor()?;
        let csr_payload = cbor!([
            Value::Integer(self.rpc_info.get_version().into()),
            Value::Text(String::from(CERT_TYPE_KEYMINT)),
            rpc_device_info,
            Value::Array(pub_cose_keys),
        ])?;
        let csr_payload_data = serialize_cbor(&csr_payload)?;
        // Construct the payload for `SignedData`
        let signed_data_payload =
            cbor!([Value::Bytes(challenge.to_vec()), Value::Bytes(csr_payload_data)])?;
        let signed_data_payload_data = serialize_cbor(&signed_data_payload)?;

        // Process DICE info.
        let dice_info =
            self.get_dice_info().ok_or_else(|| rpc_err!(Failed, "DICE info not available."))?;
        let uds_certs = read_to_value(&dice_info.pub_dice_artifacts.uds_certs)?;
        let dice_cert_chain = read_to_value(&dice_info.pub_dice_artifacts.dice_cert_chain)?;

        // Get `SignedData`
        let signed_data_cbor = read_to_value(&self.dev.rpc.sign_data_in_cose_sign1(
            &*self.imp.ec,
            &dice_info.signing_algorithm,
            &signed_data_payload_data,
            &[],
            None,
        )?)?;

        // Construct `AuthenticatedRequest<CsrPayload>`
        let authn_req = cbor!([
            Value::Integer(AUTH_REQ_SCHEMA_V1.into()),
            uds_certs,
            dice_cert_chain,
            signed_data_cbor,
        ])?;
        serialize_cbor(&authn_req)
    }
}

/// Helper function to construct `MacedPublicKey` in MacedPublicKey.aidl
fn build_maced_pub_key<F>(pub_cose_key: Vec<u8>, compute_mac: F) -> Result<Vec<u8>, Error>
where
    F: FnOnce(&[u8]) -> Result<Vec<u8>, Error>,
{
    let protected = HeaderBuilder::new().algorithm(iana::Algorithm::HMAC_256_256).build();
    let cose_mac_0 = CoseMac0Builder::new()
        .protected(protected)
        .payload(pub_cose_key)
        .try_create_tag(&[], compute_mac)?
        .build();
    Ok(cose_mac_0.to_vec().map_err(CborError::from)?)
}

/// Helper function to serialize a `cbor::value::Value` into bytes.
pub fn serialize_cbor(cbor_value: &Value) -> Result<Vec<u8>, Error> {
    let mut buf = Vec::new();
    cbor::ser::into_writer(cbor_value, &mut buf)
        .map_err(|_e| Error::Cbor(CborError::EncodeFailed))?;
    Ok(buf)
}