mirror of
https://github.com/Momoko-Ayase/Senbei.git
synced 2026-09-19 11:58:00 -04:00
refactor: consolidate platform engines into senbei-engine
This commit is contained in:
bfloat16
@@ -0,0 +1,507 @@
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//! Structural locators for protected PE stages.
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use senbei_crypto::primitives::{get_u32, lfsr_keystream};
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/// Find the 4-byte v_val that follows the LAST occurrence of `48 EB 01 B9`
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/// (REX.W jmp+1; mov ecx,imm32) plus any 0xCC padding. Used to locate
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/// stage4's accum2 seed. Works across builds even when API-name anchors are
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/// absent.
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pub fn find_v_after_pad(data: &[u8], base: u32, len: u32) -> Option<u32> {
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let start = base as usize;
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let end = (base.saturating_add(len)) as usize;
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if end > data.len() {
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return None;
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}
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let sig = [0x48u8, 0xEB, 0x01, 0xB9];
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let slice = &data[start..end];
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// last occurrence
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let mut last = None;
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let mut i = 0usize;
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while i + sig.len() <= slice.len() {
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if slice[i..i + sig.len()] == sig {
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last = Some(i);
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}
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i += 1;
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}
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let pos = last?;
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// skip CCs after the `48 EB 01 B9`
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let mut after = pos + sig.len();
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while after < slice.len() && slice[after] == 0xCC {
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after += 1;
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}
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if after + 4 > slice.len() {
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return None;
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}
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Some((start + after) as u32)
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}
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/// Predict the 4 bytes that DecryptData5(va, size) would produce at va+0..va+4
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/// without mutating the buffer. The cipher's per-byte transform depends only
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/// on the byte itself and the low 8 bits of (va+i), with no cross-byte state,
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/// so each byte can be decrypted in isolation. Used to detect the EP/DD layout
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/// offset before committing to the actual call.
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pub fn trial_decrypt5_u32(data: &[u8], va: u32) -> u32 {
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let mut out = [0u8; 4];
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for i in 0..4u32 {
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let b3 = data[(va + i) as usize];
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let b = (va + i) as u8;
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let b2 = b.wrapping_add(1);
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let b4 = b3.rotate_left(2) ^ b2;
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let b5 = b4.rotate_left(2) ^ b;
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out[i as usize] = b5.rotate_left(2);
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}
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u32::from_le_bytes(out)
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}
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/// Scan stage4/stage5 for the encrypted custom-decryptor bytecode block. The
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/// raw byte at p+95 is used by decrypt_data6 as the iteration count. We trial-
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/// decrypt that many bytes with the LFSR keystream and accept the first
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/// position where the byte stream parses as a valid opcode sequence ending in
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/// 195 (ret).
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pub fn find_bytecode_offset(data: &[u8], base: u32, len: u32) -> Option<u32> {
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let start = base as usize;
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let end = (base.saturating_add(len)) as usize;
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if end > data.len() {
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return None;
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}
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let mut ks = [0u8; 256];
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lfsr_keystream(&mut ks);
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// Scan forward from `start+16` on 16-byte boundaries relative to `start`.
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// The bytecode block is positioned a fixed offset into stage4/stage5; the
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// lowest parseable candidate is the real one (later ones are coincidental
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// parses of trailing filler bytes that happen to map to valid opcodes).
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// The enclosing buffer isn't necessarily 16-aligned to its absolute
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// address in newer builds, so we anchor the stride to `start`.
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let mut p = start + 16;
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while p + 96 <= end {
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let count = data[p + 95] as usize;
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if count >= 8 && p + count <= end {
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let mut buf = [0u8; 256];
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let take = count.min(256);
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for i in 0..take {
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buf[i] = data[p + i] ^ ks[i];
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}
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if let Some(nops) = parse_bytecode_check(&buf[..take])
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&& nops >= 4
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{
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return Some(p as u32);
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}
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}
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p += 16;
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}
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None
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}
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/// Validate bytecode structure without allocating a `Vec` of ops. Returns
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/// `Some(non_nop_op_count)` if the byte stream parses successfully as a valid
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/// opcode sequence ending in 195 (ret), `None` otherwise. Allows non-trivial
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/// bytecode filtering by op count.
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pub fn parse_bytecode_check(buf: &[u8]) -> Option<usize> {
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let mut i = 0usize;
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let mut nops: usize = 0;
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while i < buf.len() {
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let b = buf[i];
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i += 1;
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match b {
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4 | 44 | 52 => {
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if i >= buf.len() {
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return None;
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}
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i += 1;
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nops += 1;
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}
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144 => {}
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192 | 254 => {
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if i >= buf.len() {
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return None;
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}
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let mb = buf[i];
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i += 1;
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let rm = mb & 7;
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let mod_ = (mb >> 6) & 3;
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let reg = (mb >> 3) & 7;
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if mod_ != 3 || rm != 0 {
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return None;
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}
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if reg > 1 {
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return None;
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}
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if b == 192 {
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if i >= buf.len() {
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return None;
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}
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i += 1;
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}
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nops += 1;
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}
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195 => return Some(nops),
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_ => return None,
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}
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}
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None
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}
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/// Locate stage3's v4_val: the last non-zero dword in the buffer, anchored
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/// by the `C3 CC CC CC` (ret + 3 int3) immediately before it.
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pub fn find_v4_offset(data: &[u8], base: u32, len: u32) -> Option<u32> {
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let start = base as usize;
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let end = (base.saturating_add(len)) as usize;
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if end > data.len() || end < start + 4 {
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return None;
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}
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// walk backwards looking for the first non-zero byte
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let mut i = end;
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while i > start && data[i - 1] == 0 {
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i -= 1;
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}
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if i < start + 4 {
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return None;
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}
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// v_val occupies the 4 bytes ending at i (rounded up to dword boundary)
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let v_end = i;
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let v_start = ((v_end + 3) & !3).saturating_sub(4);
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// require that the 4 bytes preceding v_val match `C3 CC CC CC`
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if v_start < start + 4 || data[v_start - 4..v_start] != [0xC3, 0xCC, 0xCC, 0xCC] {
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return None;
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}
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Some(v_start as u32)
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}
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/// Scan a sub-buffer for an ASCII needle; return its absolute position.
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pub fn find_str_pos(data: &[u8], base: u32, len: u32, needle: &[u8]) -> Option<u32> {
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let start = base as usize;
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let end = (base.saturating_add(len)) as usize;
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if end > data.len() || needle.is_empty() {
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return None;
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}
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data[start..end]
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.windows(needle.len())
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.position(|w| w == needle)
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.map(|rel| (start + rel) as u32)
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}
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pub fn get_string_to_null(data: &[u8], offset: u32) -> String {
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let start = offset as usize;
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if start >= data.len() {
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return String::new();
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}
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// Bounded: an unterminated run must never walk off the end of the buffer
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// (panic) or scan unboundedly into unrelated data.
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let limit = start.saturating_add(4096).min(data.len());
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let mut i = start;
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while i < limit && data[i] != 0 {
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i += 1;
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}
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String::from_utf8_lossy(&data[start..i]).into_owned()
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}
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/// Read a PE section-name field: exactly 8 bytes, NOT necessarily
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/// NUL-terminated (a full-width name like `.textbss` has no NUL at all).
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/// Returns the name with trailing NULs stripped. Using `get_string_to_null`
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/// here would run past the field into the VirtualSize/VirtualAddress dwords.
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pub fn section_name(data: &[u8], offset: u32) -> String {
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let start = offset as usize;
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let Some(field) = data.get(start..start + 8) else {
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return String::new();
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};
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let end = field.iter().position(|&b| b == 0).unwrap_or(8);
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String::from_utf8_lossy(&field[..end]).into_owned()
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}
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// ---------------------------------------------------------------------------
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// PE32 (32-bit) helpers
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// ---------------------------------------------------------------------------
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/// PE32 shell-table locator. Walks the shell region (`info[6]`) for a dword
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/// equal to `info[6]` followed by a plausible shell size, returning the table
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/// base (`candidate = off - 0x88`) when `candidate+0x58` holds a valid pointer.
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pub fn find_tbl_pe32(data: &[u8], info: &[u32; 8]) -> Option<u32> {
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let shell = info[6];
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if (data.len() as u64) < 0x100 {
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return None;
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}
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let hi = (shell as u64)
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.saturating_add(0x3000)
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.min(data.len() as u64 - 0x100) as u32;
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let mut off = shell;
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while off < hi {
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if off as usize + 8 <= data.len() {
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let candidate = off.wrapping_sub(0x88);
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if candidate >= shell && get_u32(data, off) == info[6] {
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let shell_size_val = get_u32(data, off.wrapping_add(4));
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if shell_size_val > 0x1000 && shell_size_val < 0x100000 {
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let v58_off = candidate.wrapping_add(0x58);
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if (v58_off as usize + 4) <= data.len() {
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let v58 = get_u32(data, v58_off);
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if v58 > 0 && (v58 as usize) < data.len() {
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return Some(candidate);
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}
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}
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}
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}
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}
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off = off.wrapping_add(4);
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}
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None
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}
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/// Locate an LFSR-encrypted bytecode block (decrypt_data6 form) in a region.
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/// `start_off` is the byte offset to begin scanning at, `scan_backward`
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/// controls direction. Returns the relative offset of the block. Includes full
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/// opcode-walk validation of candidate blocks.
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pub fn find_lfsr_block(
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data: &[u8],
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base: u32,
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size: u32,
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start_off: u32,
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scan_backward: bool,
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) -> Option<u32> {
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if size < 96 {
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return None;
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}
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let mut ks = [0u8; 128];
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lfsr_keystream(&mut ks);
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let check = |scan_off: u32| -> bool {
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let abs_off = base.wrapping_add(scan_off) as usize;
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if abs_off + 96 > data.len() {
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return false;
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}
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let sz = data[abs_off + 95] as usize;
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if !(10..=95).contains(&sz) {
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return false;
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}
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let mut decoded = [0u8; 95];
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for bi in 0..sz {
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decoded[bi] = data[abs_off + bi] ^ ks[bi];
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}
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// Full bytecode validation (shared with the stage4/5 locator): every
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// opcode must decode with a valid ModR/M and the stream must REACH a
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// RET (0xC3) as an opcode. The previous check only required a 0xC3
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// byte *anywhere* in the window and accepted a walk that ran off the
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// end without hitting RET — a `0x04 0xC3` (ADD 0xC3) tail passed, so
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// coincidental LFSR-shaped garbage was accepted as a decryptor block.
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parse_bytecode_check(&decoded[..sz]).is_some()
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};
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if scan_backward {
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let hi = size - 96;
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if hi >= start_off {
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let mut scan_off = hi;
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loop {
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if check(scan_off) {
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return Some(scan_off);
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}
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if scan_off == start_off {
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break;
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}
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scan_off -= 1;
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}
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}
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} else {
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let hi = size - 95;
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let mut scan_off = start_off;
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while scan_off < hi {
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if check(scan_off) {
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return Some(scan_off);
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}
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scan_off += 1;
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}
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}
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None
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}
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/// Slots discovered in the eighthStage for the marker-less layout.
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pub struct EighthSlots {
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/// Absolute address of the file-data decryptor LFSR bytecode block. The
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/// fileCS chain pointer is derived downstream as `file_lfsr - 0x58`.
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pub file_lfsr: u32,
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/// Absolute address of the compressedInfo (ptr,size) table pointer slot.
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pub compressed_info_ptr: u32,
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}
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/// Marker-independent eighthStage slot discovery (PE32+ branch).
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///
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/// Newer Crackproof builds (e.g. some native/managed DLLs) omit the
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/// `pm\0\0cm\0\0` and `00 00 00 40 01 00 00 00` markers that the older layout's
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/// walk3/walk4/walk5 slot derivation relies on. Instead this discovers the
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/// slots structurally:
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/// * Scan the eighthStage for every LFSR (decrypt_data6) bytecode block.
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/// * The file decryptor is the LFSR block whose `fileCS = lfsr - 0x58` holds
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/// a pointer sitting just past `info[3]` (smallest positive distance).
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/// * `compressedInfo` is the pointer slot whose 16-byte target, after a
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/// trial `decrypt_data5`, parses as a plausible (src,sSize,dst,dSize)
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/// descriptor.
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///
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/// Returns `None` if no plausible file LFSR is found. `eighth_start`/`eighth_dsz`
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/// bound the search region; `info3` is `info[3]`; `compress_data_offset` is
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/// `(!u32(file_data,0x1080)) + 0x1000`; `file_data_len` is the protected file
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/// length.
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#[allow(clippy::too_many_arguments)]
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pub fn discover_eighth_slots(
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data: &[u8],
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eighth_start: u32,
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eighth_dsz: u32,
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info3: u32,
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compress_data_offset: u32,
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file_data_len: u32,
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) -> Option<EighthSlots> {
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// Collect all LFSR candidates (forward scan).
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//
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// Advance by 1 after each hit, NOT by 96. A false-positive LFSR match can sit
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// just before the real file-decryptor block (observed on an il2cpp game
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// assembly build, 2026-07-13: junk at rel=0x31C1, real block at 0x3210).
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// Stepping by the LFSR body size then skips the real block and discovery
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// fails. Byte-stepping is cheap: eighthStage is only a few KB.
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let mut all_lfsrs: Vec<u32> = Vec::new();
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let mut scan_off: u32 = 0;
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while scan_off + 95 < eighth_dsz {
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match find_lfsr_block(data, eighth_start, eighth_dsz, scan_off, false) {
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Some(found) => {
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all_lfsrs.push(found);
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scan_off = found + 1;
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}
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None => break,
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}
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}
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// Pick the file LFSR: prefer the candidate whose fileCS pointer sits the
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// smallest positive distance past info[3].
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let mut off_file_lfsr: Option<u32> = None;
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let mut best_dist: Option<u32> = None;
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for &lfsr_off in &all_lfsrs {
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if lfsr_off < 0x58 {
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continue;
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}
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let cs_off = lfsr_off - 0x58;
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let cs_val = get_u32(data, eighth_start.wrapping_add(cs_off));
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if !(0x1000 < cs_val && (cs_val as usize) < data.len()) {
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continue;
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}
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if cs_val < info3 {
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continue;
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}
|
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let dist = cs_val - info3;
|
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if best_dist.is_none_or(|b| dist < b) {
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best_dist = Some(dist);
|
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off_file_lfsr = Some(lfsr_off);
|
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}
|
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}
|
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// Fallback: last LFSR with any in-image fileCS pointer.
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if off_file_lfsr.is_none() {
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for &lfsr_off in all_lfsrs.iter().rev() {
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if lfsr_off < 0x58 {
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continue;
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}
|
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let cs_val = get_u32(data, eighth_start.wrapping_add(lfsr_off - 0x58));
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||||
if 0x1000 < cs_val && (cs_val as usize) < data.len() {
|
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off_file_lfsr = Some(lfsr_off);
|
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break;
|
||||
}
|
||||
}
|
||||
}
|
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let off_file_lfsr = off_file_lfsr?;
|
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let off_file_cs = off_file_lfsr - 0x58;
|
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|
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// Trial-decrypt to find compressedInfo: the pointer slot in the data area
|
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// (between fileCS region start and the LFSR) whose target parses as a valid
|
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// (src,sSize,dst,dSize) descriptor after a transient decrypt_data5.
|
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let scan_from = off_file_lfsr.saturating_sub(0x400);
|
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let mut off_compressed_info: Option<u32> = None;
|
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let mut doff = scan_from;
|
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while doff < off_file_lfsr {
|
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if doff == off_file_cs {
|
||||
doff += 4;
|
||||
continue;
|
||||
}
|
||||
let ptr_val = get_u32(data, eighth_start.wrapping_add(doff));
|
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if !(0x1000 < ptr_val && (ptr_val as usize) < data.len().saturating_sub(16)) {
|
||||
doff += 4;
|
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continue;
|
||||
}
|
||||
// Predict decrypt_data5(ptr_val, 16) without mutating: each dword is
|
||||
// position-keyed and independent, so trial_decrypt5_u32 per dword.
|
||||
let src2 = trial_decrypt5_u32(data, ptr_val);
|
||||
let s_sz2 = trial_decrypt5_u32(data, ptr_val + 4);
|
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let dst2 = trial_decrypt5_u32(data, ptr_val + 8);
|
||||
let d_sz2 = trial_decrypt5_u32(data, ptr_val + 12);
|
||||
let src_file_off = src2.wrapping_add(compress_data_offset);
|
||||
let valid = s_sz2 > 0
|
||||
&& s_sz2 < 0x200000
|
||||
&& (src_file_off as u64 + s_sz2 as u64) <= file_data_len as u64
|
||||
&& dst2 >= 0x1000
|
||||
&& (dst2 as u64 + d_sz2 as u64) <= data.len() as u64
|
||||
&& d_sz2 >= s_sz2
|
||||
&& d_sz2 < 0x200000;
|
||||
if valid {
|
||||
off_compressed_info = Some(doff);
|
||||
break;
|
||||
}
|
||||
doff += 4;
|
||||
}
|
||||
let off_compressed_info = off_compressed_info?;
|
||||
|
||||
Some(EighthSlots {
|
||||
file_lfsr: eighth_start.wrapping_add(off_file_lfsr),
|
||||
compressed_info_ptr: eighth_start.wrapping_add(off_compressed_info),
|
||||
})
|
||||
}
|
||||
|
||||
#[cfg(test)]
|
||||
mod tests {
|
||||
use super::*;
|
||||
|
||||
/// Task 4.1 regression: build a synthetic buffer whose valid bytecode block
|
||||
/// sits PAST `len` but within `len*2`. Assert that the smaller window misses
|
||||
/// it and the doubled window finds it.
|
||||
#[test]
|
||||
fn bytecode_locate_double_window_retry() {
|
||||
// We place the block at offset (base + len + 16) which is inside
|
||||
// the len*2 window but outside the len window.
|
||||
let base: u32 = 0;
|
||||
let len: u32 = 256;
|
||||
// Block sits at base + len + 16 = 272, aligned to 16.
|
||||
let block_pos: usize = (base + len + 16) as usize; // 272
|
||||
|
||||
// The buffer must be large enough for the block (block_pos + 96 bytes).
|
||||
let buf_len = block_pos + 256;
|
||||
let mut buf = vec![0u8; buf_len];
|
||||
|
||||
// Build a valid plaintext op stream:
|
||||
// [4, 0, 4, 0, 4, 0, 4, 0, 195] (4 ADD-AL ops then RET)
|
||||
// Padded to 10 bytes total; count >= 8.
|
||||
let count: usize = 10;
|
||||
let mut plain = [0u8; 256];
|
||||
plain[0] = 4;
|
||||
plain[1] = 0;
|
||||
plain[2] = 4;
|
||||
plain[3] = 0;
|
||||
plain[4] = 4;
|
||||
plain[5] = 0;
|
||||
plain[6] = 4;
|
||||
plain[7] = 0;
|
||||
plain[8] = 195; // ret
|
||||
|
||||
// Compute the LFSR keystream and XOR the first `count` bytes to get the
|
||||
// encrypted representation that the scanner would decrypt back.
|
||||
let mut ks = [0u8; 256];
|
||||
lfsr_keystream(&mut ks);
|
||||
for i in 0..count {
|
||||
buf[block_pos + i] = plain[i] ^ ks[i];
|
||||
}
|
||||
// Raw count byte at block_pos+95 (outside the XOR range since count=10 < 95).
|
||||
buf[block_pos + 95] = count as u8;
|
||||
|
||||
// Verify our construction: find_bytecode_offset with len should NOT find it.
|
||||
assert_eq!(
|
||||
find_bytecode_offset(&buf, base, len),
|
||||
None,
|
||||
"smaller window should not find the block"
|
||||
);
|
||||
|
||||
// The doubled window should find it at block_pos.
|
||||
assert_eq!(
|
||||
find_bytecode_offset(&buf, base, len.saturating_mul(2)),
|
||||
Some(block_pos as u32),
|
||||
"doubled window should locate the block"
|
||||
);
|
||||
}
|
||||
}
|
||||
Reference in New Issue
Block a user