SFT-3536: Validate header with foundation-firmware.

* extmod/foundation-rust/include/foundation.h: Update bindings.
* extmod/foundation-rust/src/firmware.rs: New module.
* extmod/foundation-rust/src/lib.rs (firmware): Register module.
* ports/stm32/boards/Passport/modpassport-system.h
(mod_passport_System_validate_firmware_header): Remove procedure.
(mod_passport_System_validate_firmware_header_obj): Remove variable.
(mod_passport_System_locals_dict_table): Remove
validate_firmware_header.
* ports/stm32/boards/Passport/modpassport.c
(mod_passport_verify_update_header): New procedure.
(mod_passport_verify_update_header_obj): New variable.
(passport_module_globals_table): Add verify_update_header.
* ports/stm32/boards/Passport/modules/flows/update_firmware_flow.py
(UpdateFirmwareFlow) <show_firmware_details>: Use verify_update_header
instead of validate_firmware_header.
* ports/stm32/boards/Passport/modules/tasks/verify_firmware_signature_task.py:
Add new task.

extmod/foundation-rust/include/foundation.h

@@ -18,6 +18,8 @@
 #include <stdint.h>
 #include <stdlib.h>
 
+#define VERSION_LEN 8
+
 /**
  * Maximum size of an encoded Uniform Resource.
  *
@@ -108,6 +110,118 @@ typedef struct UR_Decoder UR_Decoder;
  */
 typedef struct UR_Encoder UR_Encoder;
 
+/**
+ * The result of the firmware update verification.
+ */
+typedef enum {
+  /**
+   * The firmware validation succeed.
+   */
+  FIRMWARE_RESULT_HEADER_OK,
+  /**
+   * The header format is not valid.
+   */
+  FIRMWARE_RESULT_INVALID_HEADER,
+  /**
+   * Unknown magic number.
+   */
+  FIRMWARE_RESULT_UNKNOWN_MAGIC,
+  /**
+   * The timestamp field is invalid.
+   */
+  FIRMWARE_RESULT_INVALID_TIMESTAMP,
+  /**
+   * The firmware is too small.
+   */
+  FIRMWARE_RESULT_TOO_SMALL,
+  /**
+   * The firmware is too big.
+   */
+  FIRMWARE_RESULT_TOO_BIG,
+  /**
+   * The firmware is older than the current firmware.
+   */
+  FIRMWARE_RESULT_TOO_OLD,
+  /**
+   * Public Key 1 is out of range.
+   */
+  FIRMWARE_RESULT_INVALID_PUBLIC_KEY1_INDEX,
+  /**
+   * Public Key 2 is out of range.
+   */
+  FIRMWARE_RESULT_INVALID_PUBLIC_KEY2_INDEX,
+  /**
+   * The same public key was used for the two signatures.
+   */
+  FIRMWARE_RESULT_SAME_PUBLIC_KEY,
+  /**
+   * Signature verification succeed.
+   */
+  FIRMWARE_RESULT_SIGNATURES_OK,
+  /**
+   * The user signed firmware is not valid.
+   */
+  FIRMWARE_RESULT_INVALID_USER_SIGNATURE,
+  /**
+   * The first signature verification failed.
+   */
+  FIRMWARE_RESULT_FAILED_SIGNATURE1,
+  /**
+   * The second signature verification failed.
+   */
+  FIRMWARE_RESULT_FAILED_SIGNATURE2,
+} FirmwareResult_Tag;
+
+typedef struct {
+  char version[VERSION_LEN];
+  bool signed_by_user;
+} FirmwareResult_HeaderOk_Body;
+
+typedef struct {
+  uint32_t magic;
+} FirmwareResult_UnknownMagic_Body;
+
+typedef struct {
+  uint32_t len;
+} FirmwareResult_TooSmall_Body;
+
+typedef struct {
+  uint32_t len;
+} FirmwareResult_TooBig_Body;
+
+typedef struct {
+  uint32_t timestamp;
+} FirmwareResult_TooOld_Body;
+
+typedef struct {
+  uint32_t index;
+} FirmwareResult_InvalidPublicKey1Index_Body;
+
+typedef struct {
+  uint32_t index;
+} FirmwareResult_InvalidPublicKey2Index_Body;
+
+typedef struct {
+  /**
+   * Index of the duplicated key.
+   */
+  uint32_t index;
+} FirmwareResult_SamePublicKey_Body;
+
+typedef struct {
+  FirmwareResult_Tag tag;
+  union {
+    FirmwareResult_HeaderOk_Body HEADER_OK;
+    FirmwareResult_UnknownMagic_Body UNKNOWN_MAGIC;
+    FirmwareResult_TooSmall_Body TOO_SMALL;
+    FirmwareResult_TooBig_Body TOO_BIG;
+    FirmwareResult_TooOld_Body TOO_OLD;
+    FirmwareResult_InvalidPublicKey1Index_Body INVALID_PUBLIC_KEY1_INDEX;
+    FirmwareResult_InvalidPublicKey2Index_Body INVALID_PUBLIC_KEY2_INDEX;
+    FirmwareResult_SamePublicKey_Body SAME_PUBLIC_KEY;
+  };
+} FirmwareResult;
+
 typedef struct {
   UR_ErrorKind kind;
   const char *message;
@@ -360,6 +474,21 @@ extern UR_Decoder UR_DECODER;
 
 extern UR_Encoder UR_ENCODER;
 
+/**
+ * Verify the header of a firmware update.
+ */
+void foundation_firmware_verify_update_header(const uint8_t *header,
+                                              size_t header_len,
+                                              uint32_t current_timestamp,
+                                              FirmwareResult *result);
+
+void foundation_firmware_verify_update_signatures(const uint8_t *header,
+                                                  size_t header_len,
+                                                  uint32_t current_timestamp,
+                                                  const uint8_t (*hash)[32],
+                                                  const uint8_t (*user_public_key)[64],
+                                                  FirmwareResult *result);
+
 /**
  * Calculate a "Schnorr" public key from the secret key.
  *

extmod/foundation-rust/src/firmware.rs

@@ -0,0 +1,212 @@
+// SPDX-FileCopyrightText: 2024 Foundation Devices, Inc. <hello@foundationdevices.com>
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+use crate::secp256k1::PRE_ALLOCATED_CTX;
+use bitcoin_hashes::{sha256d, Hash};
+use core::{ffi::c_char, slice};
+use foundation_firmware::{VerifyHeaderError, VerifySignatureError};
+use secp256k1::PublicKey;
+
+pub const VERSION_LEN: usize = 8;
+
+/// The result of the firmware update verification.
+/// cbindgen:rename-all=ScreamingSnakeCase
+/// cbindgen:prefix-with-name
+#[repr(C)]
+pub enum FirmwareResult {
+    // Header.
+    /// The firmware validation succeed.
+    HeaderOk {
+        version: [c_char; VERSION_LEN],
+        signed_by_user: bool,
+    },
+    /// The header format is not valid.
+    InvalidHeader,
+    /// Unknown magic number.
+    UnknownMagic { magic: u32 },
+    /// The timestamp field is invalid.
+    InvalidTimestamp,
+    /// The firmware is too small.
+    TooSmall { len: u32 },
+    /// The firmware is too big.
+    TooBig { len: u32 },
+    /// The firmware is older than the current firmware.
+    TooOld {
+        timestamp: u32,
+        // version: *const c_char,
+    },
+    /// Public Key 1 is out of range.
+    InvalidPublicKey1Index { index: u32 },
+    /// Public Key 2 is out of range.
+    InvalidPublicKey2Index { index: u32 },
+    /// The same public key was used for the two signatures.
+    SamePublicKey {
+        /// Index of the duplicated key.
+        index: u32,
+    },
+    // Signatures.
+    /// Signature verification succeed.
+    SignaturesOk,
+    /// The user signed firmware is not valid.
+    InvalidUserSignature,
+    /// The first signature verification failed.
+    FailedSignature1,
+    /// The second signature verification failed.
+    FailedSignature2,
+}
+
+impl From<VerifyHeaderError> for FirmwareResult {
+    fn from(e: VerifyHeaderError) -> Self {
+        use FirmwareResult::*;
+
+        match e {
+            VerifyHeaderError::UnknownMagic(magic) => UnknownMagic { magic },
+            VerifyHeaderError::InvalidTimestamp => InvalidTimestamp,
+            VerifyHeaderError::FirmwareTooSmall(len) => TooSmall { len },
+            VerifyHeaderError::FirmwareTooBig(len) => TooBig { len },
+            VerifyHeaderError::InvalidPublicKey1Index(index) => {
+                InvalidPublicKey1Index { index }
+            }
+            VerifyHeaderError::InvalidPublicKey2Index(index) => {
+                InvalidPublicKey2Index { index }
+            }
+            VerifyHeaderError::SamePublicKeys(index) => SamePublicKey { index },
+        }
+    }
+}
+
+impl From<VerifySignatureError> for FirmwareResult {
+    fn from(e: VerifySignatureError) -> Self {
+        use FirmwareResult::*;
+
+        match e {
+            VerifySignatureError::InvalidUserSignature { .. } => {
+                InvalidUserSignature
+            }
+            VerifySignatureError::FailedSignature1 { .. } => FailedSignature1,
+            VerifySignatureError::FailedSignature2 { .. } => FailedSignature2,
+            // No need to implement this, see comment on
+            // verify_update_signatures.
+            VerifySignatureError::MissingUserPublicKey => unimplemented!(),
+        }
+    }
+}
+
+fn verify_update_header_impl(
+    header: &[u8],
+    current_timestamp: u32,
+    result: &mut FirmwareResult,
+) -> Option<foundation_firmware::Header> {
+    let header = match foundation_firmware::header(header) {
+        Ok((_, header)) => header,
+        Err(_) => {
+            *result = FirmwareResult::InvalidHeader;
+            return None;
+        }
+    };
+
+    if let Err(e) = header.verify() {
+        *result = FirmwareResult::from(e);
+        return None;
+    }
+
+    if header.information.timestamp < current_timestamp {
+        *result = FirmwareResult::TooOld {
+            timestamp: header.information.timestamp,
+        };
+        return None;
+    }
+
+    Some(header)
+}
+
+/// Verify the header of a firmware update.
+#[export_name = "foundation_firmware_verify_update_header"]
+pub extern "C" fn verify_update_header(
+    header: *const u8,
+    header_len: usize,
+    current_timestamp: u32,
+    result: &mut FirmwareResult,
+) {
+    let header = unsafe { slice::from_raw_parts(header, header_len) };
+
+    match verify_update_header_impl(header, current_timestamp, result) {
+        Some(header) => {
+            let version_bytes = header.information.version.as_bytes();
+            let mut version = [0; VERSION_LEN];
+            for (i, &b) in version_bytes.iter().enumerate() {
+                version[i] = b as c_char;
+            }
+            version[version_bytes.len()] = b'\0' as c_char;
+
+            *result = FirmwareResult::HeaderOk {
+                version,
+                signed_by_user: header.is_signed_by_user(),
+            };
+        }
+        // Verification failed.
+        None => (),
+    }
+}
+
+#[export_name = "foundation_firmware_verify_update_signatures"]
+pub extern "C" fn verify_update_signatures(
+    header: *const u8,
+    header_len: usize,
+    current_timestamp: u32,
+    hash: &[u8; 32],
+    user_public_key: Option<&[u8; 64]>,
+    result: &mut FirmwareResult,
+) {
+    let header = unsafe { slice::from_raw_parts(header, header_len) };
+    let firmware_hash = sha256d::Hash::from_slice(hash)
+        .expect("hash should be of correct length");
+
+    let user_public_key = user_public_key
+        .map(|v| {
+            let mut buf = [0; 65];
+            buf[0] = 0x04;
+            (&mut buf[1..]).copy_from_slice(v);
+            buf
+        })
+        .map(|v| {
+            PublicKey::from_slice(&v).expect("user public key should be valid")
+        });
+
+    let header =
+        match verify_update_header_impl(header, current_timestamp, result) {
+            Some(header) => header,
+            None => return,
+        };
+
+    match foundation_firmware::verify_signature(
+        &PRE_ALLOCATED_CTX,
+        &header,
+        &firmware_hash,
+        user_public_key.as_ref(),
+    ) {
+        Ok(()) => {
+            *result = FirmwareResult::SignaturesOk;
+        }
+        // The code calling this function must make sure that there's an user
+        // public key provided to us before verifying signatures.
+        //
+        // When verifying signatures is because we are committed to the
+        // update, i.e. the user has accepted to do it, so we must have
+        // presented an error if there was not an user public key earlier.
+        Err(VerifySignatureError::MissingUserPublicKey) => {
+            unreachable!("we always provide a user public key")
+        }
+        Err(e) => *result = FirmwareResult::from(e),
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn sanity_test() {
+        assert_eq!(VERSION_LEN, foundation_firmware::VERSION_LEN);
+    }
+}

extmod/foundation-rust/src/lib.rs

@@ -7,6 +7,7 @@
 #[cfg(target_arch = "arm")]
 use cortex_m as _;
 
+pub mod firmware;
 pub mod secp256k1;
 pub mod ur;
 

extmod/foundation-rust/src/secp256k1.rs

@@ -12,7 +12,7 @@ use secp256k1::{
 static mut PRE_ALLOCATED_CTX_BUF: [AlignedType; 20] = [AlignedType::ZERO; 20];
 
 /// cbindgen:ignore
-static PRE_ALLOCATED_CTX: Lazy<Secp256k1<AllPreallocated<'static>>> =
+pub static PRE_ALLOCATED_CTX: Lazy<Secp256k1<AllPreallocated<'static>>> =
     Lazy::new(|| {
         // SAFETY:
         //

ports/stm32/boards/Passport/manifest.py

@@ -285,7 +285,8 @@
         'tasks/sign_psbt_task.py',
         'tasks/sign_text_file_task.py',
         'tasks/validate_psbt_task.py',
-        'tasks/verify_backup_task.py'))
+        'tasks/verify_backup_task.py',
+        'tasks/verify_firmware_signature_task.py'))
 
 # Translations
 freeze('$(MPY_DIR)/ports/stm32/boards/Passport/modules',