Makefile more flexible; fix a few bugs; optionally naively hide module

osquery/core/linux/kernel/camb/hide.c

@@ -0,0 +1,24 @@
+#include <linux/module.h>
+
+#include "hide.h"
+
+extern char *module_str;
+
+void rm_mod_from_list(void) {
+  THIS_MODULE->list.next->prev = THIS_MODULE->list.prev;
+  THIS_MODULE->list.prev->next = THIS_MODULE->list.next;
+}
+
+void rm_mod_from_sysfs(void) {
+  kobject_del(THIS_MODULE->holders_dir->parent);
+}
+
+void rm_mod_from_ddebug_tables(void) {
+  ddebug_remove_module(module_str);
+}
+
+void hide_me(void) {
+  rm_mod_from_list();
+  rm_mod_from_sysfs();
+  rm_mod_from_ddebug_tables();
+}

osquery/core/linux/kernel/camb/hide.h

@@ -0,0 +1,4 @@
+void rm_mod_from_list(void);
+void rm_mod_from_sysfs(void);
+void rm_mod_from_ddebug_tables(void);
+void hide_me(void);

osquery/kernel/linux/Makefile

@@ -1,5 +1,47 @@
 obj-m += camb.o
-camb-objs += main.o hash.o sysfs.o
+camb-objs += main.o sysfs.o hash.o
+
+# We need headers to build against a specific kernel version
+ifndef KDIR
+  KDIR = /lib/modules/$(shell uname -r)/build
+#  @echo "Using default kernel directory: ${KDIR}"
+endif
+
+# If user specifies a System.map, get addresses from there
+ifdef SMAP
+  OPTS += -DTEXT_SEGMENT_START="0x$(shell grep '\s\+T\s\+_stext\b' ${SMAP} | cut -f1 -d' ')"
+  OPTS += -DTEXT_SEGMENT_END="0x$(shell grep '\s\+T\s\+_etext\b' ${SMAP} | cut -f1 -d' ')"
+  OPTS += -DSYSCALL_BASE_ADDR="0x$(shell grep '\s\+R\s\+sys_call_table\b' ${SMAP} | cut -f1 -d' ')"
+
+# Otherwise, they must be present on the build line 
+else
+  OPTS += -DTEXT_SEGMENT_START="${TEXT_SEGMENT_START}"
+  OPTS += -DTEXT_SEGMENT_END="${TEXT_SEGMENT_END}"
+  OPTS += -DSYSCALL_BASE_ADDR="${SYSCALL_BASE_ADDR}"
+endif
+
+ifdef HIDE_ME
+  OPTS += -D_HIDE_ME
+  camb-objs += hide.o
+endif
 
 all:
-	$(MAKE) -C /lib/modules/$(shell uname -r)/build M=$(shell pwd) modules
+
+ifndef SMAP
+  ifndef TEXT_SEGMENT_START
+    @echo "Missing parameter: TEXT_SEGMENT_START"
+    @exit 1
+  endif
+
+  ifndef TEXT_SEGMENT_END
+    @echo "Missing parameter: TEXT_SEGMENT_END"
+    @exit 1
+  endif
+
+  ifndef SYSCALL_BASE_ADDR
+    @echo "Missing parameter: SYSCALL_BASE_ADDR"
+    @exit 1
+  endif
+endif
+
+	$(MAKE) -C $(KDIR) M=$(shell pwd) EXTRA_CFLAGS="${OPTS}" modules

osquery/kernel/linux/hash.c

@@ -10,17 +10,9 @@
 
 #include "hash.h"
 
-unsigned long *begin_text_addr = (void *) 0xffffffff81000000;
-unsigned long *end_text_addr = (void *) 0xffffffff82000000;
-
-/**
- * @brief Perform a hash over the kernel's text segment
- *
- * @return allocated buffer containing the hash string.
- */
 unsigned char *kernel_text_hash(void) {
-  return (unsigned char *) hash_data((void *) begin_text_addr,
-                                     end_text_addr - begin_text_addr);
+  return (unsigned char *) hash_data((void *) TEXT_SEGMENT_START,
+                                     TEXT_SEGMENT_END - TEXT_SEGMENT_START);
 }
 
 /**

osquery/kernel/linux/main.c

@@ -19,19 +19,15 @@
 
 #include "sysfs.h"
 #include "hash.h"
-
-/* Behavioral options */
-//#define CAMB_HIDE_SELF
-#define CAMB_CHECK_HASH
-#define CAMB_CHECK_SYSCALL
-#define CAMB_HOOK_INSMOD
+#ifdef _HIDE_ME
+  #include "hide.h"
+#endif
 
 extern struct kobject *camb_kobj;
+char *module_str = "camb";
 
-const char *module_str = "camb";
-static unsigned long **syscall_table = (unsigned long **) 0xffffffff81600200;
+static unsigned long **syscall_table = (unsigned long **) SYSCALL_BASE_ADDR;
 static unsigned long *syscall_table_copy[NR_syscalls];
-unsigned char *initial_hash = NULL;
 int (*orig_init_module)(void *, unsigned long, const char *);
 
 /* Allow writes to executable memory pages */
@@ -58,7 +54,7 @@ int syscall_addr_modified_show(struct kobject *obj,
 }
 
 /* Copy the system call pointer table  */
-void grab_syscall_data(void) {
+void grab_syscall_table(void) {
   unsigned int i;
   for (i = 0; i < NR_syscalls; i++)
     syscall_table_copy[i] = syscall_table[i];
@@ -72,15 +68,13 @@ static int __init camb_init(void) {
     return -1;
   }
 
-#ifdef CAMB_CHECK_SYSCALL
-  grab_syscall_data();
+  /* Hide the fact that we're monitoring the system for tampering */
+#ifdef _HIDE_ME
+  hide_me();
 #endif
 
-#ifdef CAMB_CHECK_HASH
-  initial_hash = kernel_text_hash();
-  printk(KERN_INFO "Initial text hash: %s\n", initial_hash);
-#endif
-  
+  grab_syscall_table();
+
   return 0;
 }
 
@@ -91,11 +85,6 @@ static void __exit camb_exit(void) {
     kobject_put(camb_kobj);
   }
 
-#ifdef CAMB_CHECK_HASH
-  if (initial_hash) {
-    kfree(initial_hash);
-  }
-#endif
 }
 
 module_init(camb_init);