fix(metadata): restore IL2CPP 24.1 method indices

senbei-io/src/android/mod.rs

@@ -1,6 +1,6 @@
 //! Android target orchestration: protected AArch64 shared libraries (`.so`),
 //! app packages (`.apk` / `.apks` / `.xapk`), and the Android variant of the
-//! il2cpp method-token obfuscation.
+//! il2cpp method-token/method-index obfuscation.
 //!
 //! The protection scheme hollows out an ELF64/AArch64 shared object and moves
 //! the original bytes into an encrypted payload appended as a `SHT_LOUSER`
@@ -100,14 +100,32 @@ pub fn file_content_identity(path: &Path) -> std::io::Result<String> {
 /// implementation detail of the two-phase restore, not user-facing output).
 /// Returns the unwrapped embedded metadata blob when the restored image
 /// carries one (see the module docs); the caller decides where to write it.
-pub fn restore_so_file(input: &Path, dest: &Path, verbose: bool) -> Result<Option<Vec<u8>>> {
+struct SoRestoreContext {
+    embedded_metadata: Option<Vec<u8>>,
+    method_index_module: Option<Vec<u8>>,
+}
+
+fn restore_so_file_with_context(
+    input: &Path,
+    dest: &Path,
+    verbose: bool,
+) -> Result<SoRestoreContext> {
     let temporary = tempfile::tempdir().context("create stage-2 workspace")?;
     let stage2_dir = temporary.path().join("stage2");
-    extract_stage2(&ExtractOptions::with_defaults(
+    let extraction = extract_stage2(&ExtractOptions::with_defaults(
         input.to_path_buf(),
         stage2_dir.clone(),
     ))
     .context("extract stage-1/stage-2 payload")?;
+    let method_index_module = extraction
+        .module_registry
+        .iter()
+        .find(|module| module.command_id == 0x0c)
+        .map(|module| {
+            std::fs::read(stage2_dir.join(&module.image_path))
+                .with_context(|| format!("read decoded module 0x0C `{}`", module.image_path))
+        })
+        .transpose()?;
     restore_libil2cpp(&RestoreOptions {
         input: input.to_path_buf(),
         output: dest.to_path_buf(),
@@ -120,9 +138,14 @@ pub fn restore_so_file(input: &Path, dest: &Path, verbose: bool) -> Result<Optio
     .context("restore protected library")?;
     let restored =
         std::fs::read(dest).with_context(|| format!("read restored `{}`", dest.display()))?;
-    Ok(senbei_metadata::android::extract_embedded_metadata(
-        &restored,
-    ))
+    Ok(SoRestoreContext {
+        embedded_metadata: senbei_metadata::android::extract_embedded_metadata(&restored),
+        method_index_module,
+    })
+}
+
+pub fn restore_so_file(input: &Path, dest: &Path, verbose: bool) -> Result<Option<Vec<u8>>> {
+    Ok(restore_so_file_with_context(input, dest, verbose)?.embedded_metadata)
 }
 
 /// Content identity for cross-source deduplication: the same library may
@@ -134,8 +157,10 @@ pub fn content_identity(data: &[u8]) -> String {
     hex_digest(&digest.finalize())
 }
 
-/// Restore an il2cpp metadata blob (Android seeded permutation first, then the
-/// structural remap used by the Windows builds).
+/// Restore an il2cpp metadata blob. Paired v24.1 Android packages use the
+/// method-index profile recovered from module 0x0C; later Android layouts use
+/// the seeded MethodDef RID permutation before falling back to the structural
+/// remap used by the Windows builds.
 ///
 /// The Android variant obfuscates MethodDef RIDs with a keyed five-round
 /// permutation; the correct seed is recovered by intersecting per-image key
@@ -145,6 +170,32 @@ pub fn content_identity(data: &[u8]) -> String {
 /// canonical form. Both paths are no-ops (`remapped == 0`) on an
 /// already-clean blob.
 pub fn restore_metadata_bytes(data: &[u8]) -> anyhow::Result<(Vec<u8>, senbei_metadata::Report)> {
+    restore_metadata_bytes_with_module(data, None)
+}
+
+fn restore_metadata_bytes_with_module(
+    data: &[u8],
+    method_index_module: Option<&[u8]>,
+) -> anyhow::Result<(Vec<u8>, senbei_metadata::Report)> {
+    let version = data
+        .get(4..8)
+        .and_then(|bytes| <[u8; 4]>::try_from(bytes).ok())
+        .map(u32::from_le_bytes);
+    if version == Some(24)
+        && let Some(module) = method_index_module
+    {
+        let (out, report) = senbei_metadata::android::restore_method_indices_v24_1(data, module)
+            .map_err(anyhow::Error::new)?;
+        return Ok((
+            out,
+            senbei_metadata::Report {
+                version: report.version,
+                methods: report.methods,
+                remapped: report.changed_indices,
+                modules: 0,
+            },
+        ));
+    }
     if let Ok(discovery) = senbei_metadata::android::discover_method_token_seeds(data)
         && matches!(discovery.version, 29 | 31 | 39)
     {
@@ -190,7 +241,7 @@ pub struct EntryOutcome {
 pub enum EntryKind {
     /// A protected shared library, restored.
     So,
-    /// An il2cpp metadata blob, de-obfuscated (`remapped` tokens changed).
+    /// An il2cpp metadata blob, de-obfuscated (`remapped` method fields changed).
     Metadata { remapped: usize },
     /// A metadata blob unwrapped from a restored library's data section.
     EmbeddedMetadata,
@@ -204,12 +255,30 @@ pub enum EntryStatus {
     Duplicate,
     /// Content-probed but not a target (unprotected library).
     NotTarget,
-    /// A metadata blob whose tokens were already canonical; no copy written.
+    /// A metadata blob whose protected method fields were already canonical; no copy written.
     Unchanged,
     /// Recognised as a target but the restore failed.
     Failed(anyhow::Error),
 }
 
+struct PackageRestoreContext {
+    method_index_module: Option<Vec<u8>>,
+    verbose: bool,
+}
+
+impl PackageRestoreContext {
+    fn new(verbose: bool) -> Self {
+        Self {
+            method_index_module: None,
+            verbose,
+        }
+    }
+}
+
+fn package_entry_priority(path: &Path) -> u8 {
+    if is_so_name(path) { 0 } else { 1 }
+}
+
 /// Restore every protected library and metadata blob inside one app package.
 ///
 /// `rel` is the package's path relative to the scanned root (or its bare file
@@ -233,6 +302,7 @@ pub fn restore_package(
     let mut archive = open_package(package)?;
     let temporary = tempfile::tempdir().context("create package workspace")?;
     let mut outcomes = Vec::new();
+    let mut context = PackageRestoreContext::new(verbose);
 
     let mut direct = Vec::new();
     let mut nested = Vec::new();
@@ -261,6 +331,7 @@ pub fn restore_package(
             }
         }
     }
+    direct.sort_by_key(|(_, name)| package_entry_priority(name));
     for (index, name) in direct {
         let label = format!("{}::{}", rel.display(), name.display());
         let dest = out_root.join(rel).join(crate::job::out_name(&name));
@@ -271,12 +342,13 @@ pub fn restore_package(
             &dest,
             &temporary,
             seen,
-            verbose,
+            &mut context,
         )
         .with_context(|| format!("extract `{label}`"))?;
         outcomes.append(&mut entry_outcomes);
     }
     for (index, name) in nested {
+        let mut nested_context = PackageRestoreContext::new(verbose);
         let nested_label = rel.join(&name);
         let nested_path = extract_entry(&mut archive, index, &temporary, &nested_label)
             .with_context(|| format!("extract `{}`", nested_label.display()))?;
@@ -296,6 +368,9 @@ pub fn restore_package(
                 }
             }
         }
+        // Restore the protected library before metadata so v24.1 metadata can
+        // consume the runtime profile recovered from module 0x0C.
+        entries.sort_by_key(|(_, entry_name)| package_entry_priority(entry_name));
         // Keep the nested package's stem in the output layout so two splits
         // carrying same-named entries cannot collide.
         let base = rel.join(name.with_extension(""));
@@ -309,7 +384,7 @@ pub fn restore_package(
                 &dest,
                 &temporary,
                 seen,
-                verbose,
+                &mut nested_context,
             )
             .with_context(|| format!("extract `{label}`"))?;
             outcomes.append(&mut entry_outcomes);
@@ -328,7 +403,7 @@ fn restore_package_entry<R: Read + Seek>(
     dest: &Path,
     temporary: &tempfile::TempDir,
     seen: &mut HashSet<String>,
-    verbose: bool,
+    context: &mut PackageRestoreContext,
 ) -> Result<Vec<EntryOutcome>> {
     let entry_path = extract_entry(archive, index, temporary, Path::new(label))?;
     let entry_file =
@@ -358,10 +433,14 @@ fn restore_package_entry<R: Read + Seek>(
     if is_so {
         drop(entry_data);
         drop(entry_file);
-        return Ok(match restore_so_file(&entry_path, dest, verbose) {
-            Ok(embedded) => {
+        return Ok(
+            match restore_so_file_with_context(&entry_path, dest, context.verbose) {
+                Ok(restored) => {
+                    if let Some(module) = restored.method_index_module {
+                        context.method_index_module = Some(module);
+                    }
                     let mut outcomes = vec![outcome(EntryKind::So, EntryStatus::Restored)];
-                if let Some(blob) = embedded {
+                    if let Some(blob) = restored.embedded_metadata {
                         let meta_dest = embedded_metadata_dest(dest);
                         let status = match write_metadata_blob(&meta_dest, &blob) {
                             Ok(()) => EntryStatus::Restored,
@@ -377,12 +456,16 @@ fn restore_package_entry<R: Read + Seek>(
                     outcomes
                 }
                 Err(error) => vec![outcome(EntryKind::So, EntryStatus::Failed(error))],
-        });
+            },
+        );
     }
 
-    // Metadata entry: write only when the restore actually changed tokens —
+    // Metadata entry: write only when the restore actually changed protected method fields —
     // a clean blob needs no copy (same contract as loose metadata files).
-    let kind_and_status = match restore_metadata_bytes(&entry_data) {
+    let kind_and_status = match restore_metadata_bytes_with_module(
+        &entry_data,
+        context.method_index_module.as_deref(),
+    ) {
         Ok((out, report)) if report.remapped > 0 => {
             let kind = EntryKind::Metadata {
                 remapped: report.remapped,

senbei-io/src/job.rs

@@ -15,7 +15,7 @@ pub struct Summary {
     /// — likely to crash at runtime (e.g. 0xC0000005). Counted in addition to
     /// `unpacked` (a suspect file is still written).
     pub suspect: usize,
-    /// il2cpp `global-metadata.dat` files de-obfuscated (method tokens remapped),
+    /// il2cpp `global-metadata.dat` files de-obfuscated (protected method fields remapped),
     /// including blobs unwrapped from restored Android libraries.
     pub metadata: usize,
     /// Android app packages (`.apk`/`.apks`/`.xapk`) opened and searched.
@@ -369,7 +369,7 @@ pub fn run_folder_opts(
                 crate::ui::metadata(&bar, suppress_file_lines, &rel, report.remapped, &dest);
                 if let Some(log) = &log {
                     log.step(&format!(
-                        "META {rel:?} -> {dest:?}: v{} remapped {} method tokens",
+                        "META {rel:?} -> {dest:?}: v{} remapped {} method fields",
                         report.version, report.remapped
                     ));
                 }
@@ -506,13 +506,13 @@ pub fn run_file_v(
                 s.metadata = 1;
                 if let Some(log) = &log {
                     log.step(&format!(
-                        "META {:?} -> {:?}: v{} remapped {} method tokens",
+                        "META {:?} -> {:?}: v{} remapped {} method fields",
                         input, dest, report.version, report.remapped
                     ));
                 }
                 if quiet == 0 {
                     println!(
-                        "✓ metadata v{} -> {:?} ({} method tokens remapped)",
+                        "✓ metadata v{} -> {:?} ({} method fields remapped)",
                         report.version, dest, report.remapped
                     );
                 }

senbei-io/src/ui.rs

@@ -39,13 +39,13 @@ pub fn ok_label(bar: &ProgressBar, quiet: bool, rel: &str, label: &str, dest: &P
 }
 
 /// Print a green success line for a de-obfuscated il2cpp `global-metadata.dat`,
-/// reporting how many method tokens were remapped.
+/// reporting how many protected method fields were remapped.
 pub fn metadata(bar: &ProgressBar, quiet: bool, rel: &Path, remapped: usize, dest: &Path) {
     if quiet {
         return;
     }
     let msg = format!(
-        "{} metadata  {}  ->  {}  ({} method tokens remapped)",
+        "{} metadata  {}  ->  {}  ({} method fields remapped)",
         "✓".green(),
         rel.display(),
         dest.display(),

senbei-metadata/src/android/method_indices.rs

@@ -0,0 +1,467 @@
+//! Restoration of IL2CPP v24.1 `Il2CppMethodDefinition.methodIndex` values.
+//!
+//! CrackProof's v24.1 Android module rewrites the global method-index permutation
+//! at runtime. The transform parameters are carried by the decoded module `0x0C`,
+//! so the restore derives them from that module instead of hard-coding a
+//! game-specific table.
+
+use serde::Serialize;
+
+use crate::common::MAGIC;
+
+const RAW_VERSION_24: u32 = 24;
+const HDR_METHODS: usize = 0x30;
+const V24_1_METHOD_STRIDE: usize = 0x34;
+const V24_1_METHOD_INDEX_OFFSET: usize = 0x14;
+const V24_1_SELECTOR: u32 = 1;
+const EXCEPTION_COUNT: usize = 256;
+
+#[derive(Debug, Clone, PartialEq, Eq, Serialize)]
+pub struct MethodIndexReport {
+    pub version: u32,
+    pub methods: usize,
+    pub active_methods: usize,
+    pub changed_indices: usize,
+    pub exception_count: usize,
+    pub seed: String,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq, thiserror::Error)]
+pub enum MethodIndexError {
+    #[error("not an IL2CPP global-metadata.dat")]
+    NotMetadata,
+    #[error("unsupported metadata version {0}")]
+    UnsupportedVersion(u32),
+    #[error("malformed v24.1 metadata: {0}")]
+    Malformed(String),
+    #[error("v24.1 method-index profile was not found in module 0x0C")]
+    ProfileNotFound,
+    #[error("multiple v24.1 method-index profiles matched module 0x0C")]
+    AmbiguousProfile,
+    #[error("v24.1 method-index restoration failed validation: {0}")]
+    Validation(String),
+}
+
+type Result<T> = std::result::Result<T, MethodIndexError>;
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+struct Profile {
+    seed: u32,
+    exception_values: [u32; EXCEPTION_COUNT],
+}
+
+fn bytes(data: &[u8], offset: usize, size: usize) -> Result<&[u8]> {
+    let end = offset
+        .checked_add(size)
+        .ok_or_else(|| MethodIndexError::Malformed("byte range overflow".to_owned()))?;
+    data.get(offset..end).ok_or_else(|| {
+        MethodIndexError::Malformed(format!(
+            "byte range 0x{offset:x}..0x{end:x} is out of bounds"
+        ))
+    })
+}
+
+fn read_u32(data: &[u8], offset: usize) -> Result<u32> {
+    let value: [u8; 4] = bytes(data, offset, 4)?
+        .try_into()
+        .map_err(|_| MethodIndexError::Malformed("invalid u32 range".to_owned()))?;
+    Ok(u32::from_le_bytes(value))
+}
+
+fn read_i32(data: &[u8], offset: usize) -> Result<i32> {
+    let value: [u8; 4] = bytes(data, offset, 4)?
+        .try_into()
+        .map_err(|_| MethodIndexError::Malformed("invalid i32 range".to_owned()))?;
+    Ok(i32::from_le_bytes(value))
+}
+
+fn write_i32(data: &mut [u8], offset: usize, value: i32) -> Result<()> {
+    let destination = data.get_mut(offset..offset + 4).ok_or_else(|| {
+        MethodIndexError::Malformed("method-index write is out of bounds".to_owned())
+    })?;
+    destination.copy_from_slice(&value.to_le_bytes());
+    Ok(())
+}
+
+fn method_table(data: &[u8]) -> Result<(usize, usize)> {
+    if read_u32(data, 0)? != MAGIC {
+        return Err(MethodIndexError::NotMetadata);
+    }
+    let version = read_u32(data, 4)?;
+    if version != RAW_VERSION_24 {
+        return Err(MethodIndexError::UnsupportedVersion(version));
+    }
+    let offset = read_u32(data, HDR_METHODS)? as usize;
+    let size = read_u32(data, HDR_METHODS + 4)? as usize;
+    bytes(data, offset, size)?;
+    if !size.is_multiple_of(V24_1_METHOD_STRIDE) {
+        return Err(MethodIndexError::Malformed(format!(
+            "method table size 0x{size:x} is not divisible by v24.1 stride 0x{V24_1_METHOD_STRIDE:x}"
+        )));
+    }
+    Ok((offset, size / V24_1_METHOD_STRIDE))
+}
+
+fn method_indices(data: &[u8]) -> Result<(usize, Vec<Option<u32>>)> {
+    let (offset, count) = method_table(data)?;
+    let mut indices = Vec::with_capacity(count);
+    for method in 0..count {
+        let value = read_i32(
+            data,
+            offset + method * V24_1_METHOD_STRIDE + V24_1_METHOD_INDEX_OFFSET,
+        )?;
+        indices.push((value >= 0).then_some(value as u32));
+    }
+    Ok((offset, indices))
+}
+
+fn is_complete_permutation(indices: &[Option<u32>]) -> bool {
+    let active_count = indices.iter().filter(|value| value.is_some()).count();
+    if active_count == 0 || active_count > u32::MAX as usize {
+        return false;
+    }
+    let mut seen = vec![false; active_count];
+    for value in indices.iter().flatten().copied() {
+        let Ok(index) = usize::try_from(value) else {
+            return false;
+        };
+        if index >= active_count || seen[index] {
+            return false;
+        }
+        seen[index] = true;
+    }
+    seen.into_iter().all(|value| value)
+}
+
+fn permutation_key(seed: u32, count: u32) -> Result<u32> {
+    if count < 2 {
+        return Err(MethodIndexError::Validation(
+            "method-index permutation requires at least two active methods".to_owned(),
+        ));
+    }
+    if count > u32::MAX / 2 {
+        return Err(MethodIndexError::Validation(
+            "active method count is too large for the permutation mirror".to_owned(),
+        ));
+    }
+    let half = count / 2;
+    if half == 0 {
+        return Err(MethodIndexError::Validation(
+            "method-index permutation has a zero divisor".to_owned(),
+        ));
+    }
+    Ok(seed % half + count / 4)
+}
+
+fn permutation_round(mut value: u32, count: u32, key: u32) -> u32 {
+    let mirror = count * 2 - 1;
+    if value & 1 != 0 {
+        value = mirror - value;
+    }
+    value >>= 1;
+    if value >= count {
+        value = mirror - value;
+    }
+    let adjusted = i64::from(value) - i64::from(key);
+    if adjusted < 0 {
+        (adjusted + i64::from(count)) as u32
+    } else {
+        adjusted as u32
+    }
+}
+
+fn transform_index(mut value: u32, count: u32, seed: u32) -> Result<u32> {
+    let key = permutation_key(seed, count)?;
+    for _ in 0..5 {
+        value = permutation_round(value, count, key);
+    }
+    Ok(value)
+}
+
+fn transformed_values(indices: &[Option<u32>], seed: u32) -> Result<Vec<Option<u32>>> {
+    let active_count = indices.iter().filter(|value| value.is_some()).count();
+    let count = u32::try_from(active_count)
+        .map_err(|_| MethodIndexError::Validation("active method count exceeds u32".to_owned()))?;
+    indices
+        .iter()
+        .map(|value| {
+            value
+                .map(|value| transform_index(value, count, seed))
+                .transpose()
+        })
+        .collect()
+}
+
+fn missing_values(indices: &[Option<u32>]) -> Option<Vec<u32>> {
+    let active_count = indices.iter().filter(|value| value.is_some()).count();
+    let mut seen = vec![false; active_count];
+    for value in indices.iter().flatten().copied() {
+        let index = usize::try_from(value).ok()?;
+        if index >= active_count {
+            return None;
+        }
+        seen[index] = true;
+    }
+    Some(
+        seen.into_iter()
+            .enumerate()
+            .filter_map(|(index, present)| (!present).then_some(index as u32))
+            .collect(),
+    )
+}
+
+fn find_exception_table(
+    module: &[u8],
+    count: u32,
+    missing: &[u32],
+) -> Option<[u32; EXCEPTION_COUNT]> {
+    if missing.len() != EXCEPTION_COUNT || count == 0 {
+        return None;
+    }
+    let mut wanted = vec![false; count as usize];
+    for &value in missing {
+        let slot = wanted.get_mut(value as usize)?;
+        *slot = true;
+    }
+    let table_bytes = EXCEPTION_COUNT * 4;
+    for offset in (8..=module.len().checked_sub(table_bytes)?).step_by(4) {
+        if read_u32(module, offset - 8).ok()? != V24_1_SELECTOR
+            || read_u32(module, offset - 4).ok()? != count - 1
+        {
+            continue;
+        }
+        let mut values = [0_u32; EXCEPTION_COUNT];
+        let mut seen = vec![false; count as usize];
+        let mut matches = true;
+        for (index, slot) in values.iter_mut().enumerate() {
+            let value = read_u32(module, offset + index * 4).ok()?;
+            let Some(is_wanted) = wanted.get(value as usize) else {
+                matches = false;
+                break;
+            };
+            if !*is_wanted || seen[value as usize] {
+                matches = false;
+                break;
+            }
+            seen[value as usize] = true;
+            *slot = value;
+        }
+        if matches {
+            return Some(values);
+        }
+    }
+    None
+}
+
+fn profile_candidates(module: &[u8], indices: &[Option<u32>]) -> Result<Vec<Profile>> {
+    let active_count = indices.iter().filter(|value| value.is_some()).count();
+    let count = u32::try_from(active_count)
+        .map_err(|_| MethodIndexError::Validation("active method count exceeds u32".to_owned()))?;
+    if count <= EXCEPTION_COUNT as u32 {
+        return Err(MethodIndexError::Validation(format!(
+            "active method count {count} is too small for the v24.1 exception table"
+        )));
+    }
+
+    let mut profiles = Vec::new();
+    for offset in (0..module.len().saturating_sub(8)).step_by(4) {
+        let Ok(version) = read_u32(module, offset + 4) else {
+            continue;
+        };
+        if version != RAW_VERSION_24 {
+            continue;
+        }
+        let seed = read_u32(module, offset)?;
+        let transformed = transformed_values(indices, seed)?;
+        let Some(missing) = missing_values(&transformed) else {
+            continue;
+        };
+        let Some(exception_values) = find_exception_table(module, count, &missing) else {
+            continue;
+        };
+        let mut candidate = transformed;
+        let mut exception = exception_values.iter().copied();
+        for value in candidate.iter_mut().flatten() {
+            if let Some(replacement) = exception.next() {
+                *value = replacement;
+            } else {
+                break;
+            }
+        }
+        if exception.next().is_none() && is_complete_permutation(&candidate) {
+            profiles.push(Profile {
+                seed,
+                exception_values,
+            });
+        }
+    }
+    profiles.sort_by_key(|profile| profile.seed);
+    profiles.dedup();
+    Ok(profiles)
+}
+
+/// Restore the v24.1 `methodIndex` permutation using the decoded CrackProof
+/// module `0x0C` that accompanied the protected library.
+///
+/// The profile is accepted only when the module supplies a seed plus a
+/// 256-entry exception table that turns the restored non-negative indices into
+/// the exact permutation `0..active_method_count`. This makes a wrong module or
+/// incompatible v24 sub-layout fail without mutating the metadata.
+pub fn restore_method_indices_v24_1(
+    data: &[u8],
+    module_0c: &[u8],
+) -> Result<(Vec<u8>, MethodIndexReport)> {
+    let (method_offset, indices) = method_indices(data)?;
+    let active_count = indices.iter().filter(|value| value.is_some()).count();
+    if is_complete_permutation(&indices) {
+        return Ok((
+            data.to_vec(),
+            MethodIndexReport {
+                version: RAW_VERSION_24,
+                methods: indices.len(),
+                active_methods: active_count,
+                changed_indices: 0,
+                exception_count: 0,
+                seed: "clean".to_owned(),
+            },
+        ));
+    }
+
+    let profiles = profile_candidates(module_0c, &indices)?;
+    let profile = match profiles.as_slice() {
+        [] => return Err(MethodIndexError::ProfileNotFound),
+        [profile] => profile,
+        _ => return Err(MethodIndexError::AmbiguousProfile),
+    };
+
+    let mut restored = transformed_values(&indices, profile.seed)?;
+    let mut exception = profile.exception_values.iter().copied();
+    for value in restored.iter_mut().flatten() {
+        if let Some(replacement) = exception.next() {
+            *value = replacement;
+        } else {
+            break;
+        }
+    }
+    if exception.next().is_some() {
+        return Err(MethodIndexError::Validation(
+            "metadata has fewer active methods than the exception table".to_owned(),
+        ));
+    }
+    if !is_complete_permutation(&restored) {
+        return Err(MethodIndexError::Validation(
+            "restored methodIndex values are not a complete permutation".to_owned(),
+        ));
+    }
+
+    let mut output = data.to_vec();
+    let mut changed_indices = 0_usize;
+    for (method, value) in restored.iter().enumerate() {
+        let Some(value) = value else {
+            continue;
+        };
+        let offset = method_offset + method * V24_1_METHOD_STRIDE + V24_1_METHOD_INDEX_OFFSET;
+        let old = read_i32(data, offset)?;
+        let new = i32::try_from(*value).map_err(|_| {
+            MethodIndexError::Validation("restored methodIndex exceeds i32".to_owned())
+        })?;
+        if old != new {
+            write_i32(&mut output, offset, new)?;
+            changed_indices += 1;
+        }
+    }
+
+    Ok((
+        output,
+        MethodIndexReport {
+            version: RAW_VERSION_24,
+            methods: indices.len(),
+            active_methods: active_count,
+            changed_indices,
+            exception_count: EXCEPTION_COUNT,
+            seed: format!("0x{:08X}", profile.seed),
+        },
+    ))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn inverse_map(count: u32, seed: u32) -> Vec<u32> {
+        let mut inverse = vec![u32::MAX; count as usize];
+        for value in 0..count {
+            let transformed = transform_index(value, count, seed).unwrap();
+            inverse[transformed as usize] = value;
+        }
+        assert!(inverse.iter().all(|value| *value != u32::MAX));
+        inverse
+    }
+
+    fn fixture() -> (Vec<u8>, Vec<u8>) {
+        let active_count = 512_u32;
+        let seed = 0x7770_0dcc;
+        let inverse = inverse_map(active_count, seed);
+        let header_size = 0x100usize;
+        let method_size = active_count as usize * V24_1_METHOD_STRIDE;
+        let mut metadata = vec![0_u8; header_size + method_size];
+        metadata[0..4].copy_from_slice(&MAGIC.to_le_bytes());
+        metadata[4..8].copy_from_slice(&RAW_VERSION_24.to_le_bytes());
+        metadata[HDR_METHODS..HDR_METHODS + 4].copy_from_slice(&(header_size as u32).to_le_bytes());
+        metadata[HDR_METHODS + 4..HDR_METHODS + 8]
+            .copy_from_slice(&(method_size as u32).to_le_bytes());
+
+        // Before the exception patch the first half duplicates the second half,
+        // leaving 0..255 missing. The module's 256-entry table fills exactly
+        // those first active methods after the five-round transform.
+        for method in 0..active_count as usize {
+            let transformed = 256 + (method % 256) as u32;
+            let protected = inverse[transformed as usize];
+            let offset = header_size + method * V24_1_METHOD_STRIDE + V24_1_METHOD_INDEX_OFFSET;
+            metadata[offset..offset + 4].copy_from_slice(&(protected as i32).to_le_bytes());
+        }
+
+        let mut module = vec![0_u8; 0x1000];
+        module[0x100..0x104].copy_from_slice(&seed.to_le_bytes());
+        module[0x104..0x108].copy_from_slice(&RAW_VERSION_24.to_le_bytes());
+        module[0x3f8..0x3fc].copy_from_slice(&V24_1_SELECTOR.to_le_bytes());
+        module[0x3fc..0x400].copy_from_slice(&(active_count - 1).to_le_bytes());
+        for value in 0..EXCEPTION_COUNT as u32 {
+            let offset = 0x400 + value as usize * 4;
+            module[offset..offset + 4].copy_from_slice(&value.to_le_bytes());
+        }
+        (metadata, module)
+    }
+
+    #[test]
+    fn restores_v24_1_method_index_permutation() {
+        let (metadata, module) = fixture();
+        let (restored, report) = restore_method_indices_v24_1(&metadata, &module).unwrap();
+        assert_eq!(report.active_methods, 512);
+        assert_eq!(report.exception_count, 256);
+        assert_eq!(report.seed, "0x77700DCC");
+        let (offset, indices) = method_indices(&restored).unwrap();
+        assert_eq!(offset, 0x100);
+        assert!(is_complete_permutation(&indices));
+        for (method, value) in indices.into_iter().enumerate() {
+            assert_eq!(value, Some(method as u32));
+        }
+    }
+
+    #[test]
+    fn clean_v24_1_metadata_is_idempotent() {
+        let (metadata, module) = fixture();
+        let (restored, _) = restore_method_indices_v24_1(&metadata, &module).unwrap();
+        let (again, report) = restore_method_indices_v24_1(&restored, &module).unwrap();
+        assert_eq!(again, restored);
+        assert_eq!(report.changed_indices, 0);
+        assert_eq!(report.seed, "clean");
+    }
+
+    #[test]
+    fn rejects_unrelated_module() {
+        let (metadata, _) = fixture();
+        let error = restore_method_indices_v24_1(&metadata, &[0_u8; 0x1000]).unwrap_err();
+        assert_eq!(error, MethodIndexError::ProfileNotFound);
+    }
+}

senbei-metadata/src/android/mod.rs

@@ -2,9 +2,11 @@
 
 mod embedded;
 mod keystream;
+mod method_indices;
 mod method_tokens;
 
 pub use embedded::{embedded_metadata_size, extract_embedded_metadata};
+pub use method_indices::{MethodIndexError, MethodIndexReport, restore_method_indices_v24_1};
 pub use method_tokens::{
     DEFAULT_METHOD_TOKEN_SEED, Error, ImageKeyDiscovery, Report, SeedDiscoveryReport,
     discover_method_token_seeds, restore_method_tokens,