target/earlgrey/util/boot_log.rs

// Licensed under the Apache-2.0 license
// SPDX-License-Identifier: Apache-2.0

//! Boot Log structures for OpenTitan.
//!
//! The `BootLog` is populated by early boot stages (ROM and ROM_EXT) to describe
//! the boot process, including slot choices, versions, sizes, and ownership
//! states of the loaded stages. This log is passed to the application via
//! the Retention SRAM (`RetRam.boot_log` field).

use zerocopy::{FromBytes, Immutable, IntoBytes, KnownLayout};

use crate::misc::UnalignedU64;
use crate::tags::{BootSlot, HardenedBool, OwnershipState};
use crate::CheckDigest;

/// Information about the boot flow generated by ROM and ROM_EXT.
///
/// It contains hashes, slot selections, version information, and security levels
/// of the boot components. The entire structure is protected by an integrity digest.
#[derive(Clone, FromBytes, Immutable, IntoBytes, KnownLayout)]
#[repr(C)]
pub struct BootLog {
    /// A SHA256 integrity digest computed over all subsequent fields in this structure.
    pub digest: [u8; 32],
    /// A tag identifying this structure. Must be `'BLOG'`.
    pub identifier: u32,
    /// The hardware/ROM version (typically a Git commit hash prefix).
    pub chip_version: UnalignedU64,
    /// The boot slot chosen by the ROM to run the ROM Extension (ROM_EXT).
    pub rom_ext_slot: BootSlot,
    /// ROM_EXT major version.
    pub rom_ext_major: u32,
    /// ROM_EXT minor version.
    pub rom_ext_minor: u32,
    /// ROM_EXT size in bytes.
    pub rom_ext_size: u32,
    /// Anti-replay nonce value used by ROM_EXT.
    pub rom_ext_nonce: UnalignedU64,
    /// The boot slot chosen by the ROM_EXT to run the owner application (BL0).
    pub bl0_slot: BootSlot,
    /// The chip's ownership state at boot time.
    pub ownership_state: OwnershipState,
    /// Cumulative counter of ownership transfers performed on this chip.
    pub ownership_transfers: u32,
    /// Minimum security version permitted for ROM_EXT images.
    pub rom_ext_min_sec_ver: u32,
    /// Minimum security version permitted for owner application (BL0) images.
    pub bl0_min_sec_ver: u32,
    /// The primary BL0 boot slot configured in the chip.
    pub primary_bl0_slot: BootSlot,
    /// Hardened boolean indicating if the retention RAM was freshly initialized.
    pub retention_ram_initialized: HardenedBool,
    /// Reserved space for future extensions.
    pub reserved: [u32; 8],
}

impl CheckDigest for BootLog {
    /// Validates the integrity digest of the `BootLog`.
    ///
    /// The digest is calculated over the structure bytes starting immediately
    /// after the `digest` field (byte offset 32).
    fn check_digest<F>(&self, f: F) -> bool
    where
        F: Fn(&[u8]) -> [u8; 32],
    {
        let digest = f(&self.as_bytes()[32..]);
        // OpenTitan digests are stored in reverse byte order
        for (a, b) in self.digest.iter().zip(digest.iter().rev()) {
            if *a != *b {
                return false;
            }
        }
        true
    }

    /// Computes and sets the integrity digest on the `BootLog`.
    fn set_digest<F>(&mut self, f: F)
    where
        F: Fn(&[u8]) -> [u8; 32],
    {
        let digest = f(&self.as_bytes()[32..]);
        for (a, b) in self.digest.iter_mut().zip(digest.iter().rev()) {
            *a = *b;
        }
    }
}