IntegrityCheckBypass (RE4): Fix for JP version again (#912)

praydog · Oct 4, 2023 · d7655f0 · d7655f0
1 parent 9f479ea
commit d7655f0
Showing 1 changed file with 37 additions and 4 deletions.
diff --git a/src/mods/IntegrityCheckBypass.cpp b/src/mods/IntegrityCheckBypass.cpp
@@ -439,14 +439,47 @@ void IntegrityCheckBypass::immediate_patch_re4() {
         // so we have to use the unique instruction is a reference point to scan from.
         const auto short_jmp_before = utility::scan_reverse(*unique_instruction, 0x100, "75 ? 50 F7 D0");
 
-        if (!short_jmp_before) {
-            spdlog::error("[IntegrityCheckBypass]: Could not find short_jmp_before!");
+        if (short_jmp_before) {
+            static auto patch = Patch::create(*short_jmp_before, { 0xEB }, true);
+            spdlog::info("[IntegrityCheckBypass]: Patched conditional_jmp!");
             return;
         }
 
-        static auto patch = Patch::create(*short_jmp_before, { 0xEB }, true);
-        spdlog::info("[IntegrityCheckBypass]: Patched conditional_jmp!");
+        // If we've gotten to this point, we are trying the scorched earth method of trying to obtain the function "start"
+        // for this giant obfuscated blob. We will get the instructions behind the unique_instruction we found by doing that,
+        // and look for the nearest branch instruction to patch.
+        spdlog::error("[IntegrityCheckBypass]: Could not find short_jmp_before, trying fallback.");
 
+        // Get the preceding instructions. If this doesn't work we'll need to scan for a common instruction anchor to scan forward from...
+        auto previous_instructions = utility::get_disassembly_behind(*unique_instruction);
+
+        if (previous_instructions.empty()) {
+            spdlog::error("[IntegrityCheckBypass]: Could not find previous_instructions!");
+            return;
+        }
+
+        // Reverse the order of the instructions.
+        std::reverse(previous_instructions.begin(), previous_instructions.end());
+
+        spdlog::info("[IntegrityCheckBypass]: Found {} previous instructions.", previous_instructions.size());
+        spdlog::info("[IntegrityCheckBypass]: Walking previous instructions...");
+
+        for (auto& insn : previous_instructions) {
+            if (insn.instrux.BranchInfo.IsBranch) {
+                spdlog::info("[IntegrityCheckBypass]: Found branch instruction, patching...");
+
+                if (insn.instrux.BranchInfo.IsFar) {
+                    static auto patch = Patch::create(insn.addr, { 0xE9 }, true);
+                } else {
+                    static auto patch = Patch::create(insn.addr, { 0xEB }, true);
+                }
+
+                spdlog::info("[IntegrityCheckBypass]: Patched conditional_jmp");
+                return;
+            }
+        }
+
+        spdlog::error("[IntegrityCheckBypass]: Could not find branch instruction to patch!");
         return;
     }