From f37d8b376b556f111e160ba34d20d82edd49e458 Mon Sep 17 00:00:00 2001
From: Stefano Moioli <smxdev4@gmail.com>
Date: Fri, 5 Apr 2024 02:23:45 +0200
Subject: [PATCH] backdoor_setup + backdoor_setup_params_t (partial)

---
 xzre.h   | 54 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 xzre.lds |  3 +++
 2 files changed, 57 insertions(+)

diff --git a/xzre.h b/xzre.h
index 16da386..7194265 100644
--- a/xzre.h
+++ b/xzre.h
@@ -84,6 +84,52 @@ typedef enum {
 #define EXPAND(x, y) CONCAT(x, y)
 #define PADDING(size) u8 EXPAND(_unknown, __LINE__)[size]
 
+typedef struct __attribute__((packed)) {
+	/**
+	 * @brief points to a symbol in memory
+	 * will be used to find the GOT value
+	 */
+	void *symbol_ptr;
+	/**
+	 * @brief points to the Global Offset Table
+	 */
+	void *got_ptr;
+	/**
+	 * @brief the return address value of the caller
+	 * obtained from *(u64 *)(caller_locals+24)
+	 * since the entrypoint passes __builtin_frame_address(0)-16,
+	 * this results in an offset of +8
+	 */
+	void *return_address;
+	/**
+	 * @brief points to the real cpuid function
+	 */
+	void *cpuid_fn;
+	/**
+	 * @brief holds the offset of the symbol relative to the GOT.
+	 * used to derive the @ref got_ptr
+	 */
+	u64 got_offset;
+	/**
+	 * @brief stores the value of __builtin_frame_address(0)-16
+	 */
+	u64 *caller_locals;
+} elf_entry_ctx_t;
+
+assert_offset(elf_entry_ctx_t, symbol_ptr, 0);
+assert_offset(elf_entry_ctx_t, got_ptr, 8);
+assert_offset(elf_entry_ctx_t, return_address, 0x10);
+assert_offset(elf_entry_ctx_t, cpuid_fn, 0x18);
+assert_offset(elf_entry_ctx_t, got_offset, 0x20);
+assert_offset(elf_entry_ctx_t, caller_locals, 0x28);
+
+typedef struct __attribute__((packed)) {
+	PADDING(0x80);
+	elf_entry_ctx_t *entry_ctx;
+} backdoor_setup_params_t;
+
+static_assert(sizeof(backdoor_setup_params_t) == 0x88);
+
 typedef struct __attribute__((packed)) {
 	u8* first_instruction;
 	u64 instruction_size;
@@ -738,5 +784,13 @@ extern BOOL secret_data_append_singleton(
 	secret_data_shift_cursor shift_cursor,
 	unsigned reg2reg_instruction_count, unsigned operation_index);
 
+/**
+ * @brief the backdoor main method
+ * 
+ * @param params parameters
+ * @return BOOL unused
+ */
+extern BOOL backdoor_setup(backdoor_setup_params_t *params);
+
 #include "util.h"
 #endif
\ No newline at end of file
diff --git a/xzre.lds b/xzre.lds
index 148bd30..c5c8394 100644
--- a/xzre.lds
+++ b/xzre.lds
@@ -62,5 +62,8 @@ SECTIONS {
 
         "secret_data_append_singleton" = ".";
         *(.text.rc_read_inis);
+
+        "backdoor_setup" = ".";
+        *(.text.microlzma_encoder_inia);
     }
 } INSERT AFTER .text;