feat: add spoofer

- spoofer redirects reads to /proc to ./proc

Makefile

@@ -32,6 +32,8 @@ HOST_SRC_EXTRA := src/elf.c src/hwinfo.c src/util.c tiny-AES-c/aes.c
 HOST_SRC := src/main.c $(HOST_SRC_EXTRA)
 HOST_SRC_ENCRYPTOR := src/encryptor.c $(HOST_SRC_EXTRA)
 HOST_INCLUDE := -I src -I tinyriscv/src -I tiny-AES-c
+HOST_SRC_SPOOFER := src/spoof/spoofer.c
+
 
 ifeq ($(OS),Windows_NT)
     HOST_EXE := build/main.exe
@@ -45,6 +47,8 @@ else
     HOST_EXE_ENCRYPTOR := build/encryptor
 endif
 
+HOST_EXE_SPOOFER := build/spoofer
+
 
 # Disassembly
 RISCV_OBJDUMP ?= $(patsubst %-gcc,%-objdump,$(RISCV_CC))
@@ -55,16 +59,20 @@ _DISAS_FILES   := $(if $(_DISAS_TARGETS),$(filter %.elf %.o,$(MAKECMDGOALS)))
 
 .PHONY: all emulated-riscv host clean disas-risc
 
-all: $(ZIP_FILE)
+all: $(ZIP_FILE) $(HOST_EXE_SPOOFER)
 
 emulated-riscv: $(EMU_OBJ_LICENSE)
 
-host: $(HOST_EXE)
+host: $(HOST_EXE) $(HOST_EXE_SPOOFER)
 
 # Build the main challenge executable
 $(HOST_EXE): $(HOST_SRC) | build
 	$(HOST_CC) $(HOST_CFLAGS) $(HOST_LDFLAGS) $(HOST_INCLUDE) $(HOST_SRC) -o $@
 
+# Build the spoofer
+$(HOST_EXE_SPOOFER): $(HOST_SRC_SPOOFER) | build
+	$(HOST_CC) $(HOST_CFLAGS) $(HOST_LDFLAGS) -shared -fPIC $^ -o $@ -ldl
+
 # Build the encryptor
 $(HOST_EXE_ENCRYPTOR): $(HOST_SRC_ENCRYPTOR) | build
 	$(HOST_CC) $(HOST_CFLAGS) $(HOST_LDFLAGS) $(HOST_INCLUDE) $(HOST_SRC_ENCRYPTOR) -o $@

src/spoof/spoofer.c

@@ -0,0 +1,39 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <dlfcn.h>
+
+static FILE *(*real_fopen)(const char *path, const char *mode) = NULL;
+
+static void init_real_fopen(void) {
+    if (!real_fopen) {
+        real_fopen = dlsym(RTLD_NEXT, "fopen");
+        if (!real_fopen) {
+            fprintf(stderr, "proc_redirect: dlsym(fopen) failed: %s\n", dlerror());
+            abort();
+        }
+    }
+}
+
+FILE *fopen(const char *path, const char *mode) {
+    init_real_fopen();
+
+    if (path && strncmp(path, "/proc/", 6) == 0) {
+        const char *rel_suffix = path + 1;
+        size_t len = strlen(rel_suffix) + 3;
+        char *new_path = malloc(len);
+        if (!new_path) {
+            fprintf(stderr, "proc_redirect: malloc failed\n");
+            abort();
+        }
+        new_path[0] = '.';
+        new_path[1] = '/';
+        strcpy(new_path + 2, rel_suffix);
+
+        FILE *f = real_fopen(new_path, mode);
+        free(new_path);
+        return f;
+    }
+
+    return real_fopen(path, mode);
+}