通过xnuspy hook 内核ptrace 函数绕过反调试

昨天实践了修改kernproc 结构体绕过反调试.今天突然想到是不是直接内核hook 更方便点儿

0x01先阅读自己手机系统iPhone 7 的 14.1对应的xnu开源代码里面的ptrace代码

  • xnu-xnu-7195.50.7.100.1/bsd/kern/mach_process.c

int
ptrace(struct proc *p, struct ptrace_args *uap, int32_t *retval)
{
	struct proc     *t; /* target process */
	task_t          task;
	thread_t        th_act;
	struct uthread  *ut;
	int tr_sigexc = 0;
	int error = 0;
	int stopped = 0;

	AUDIT_ARG(cmd, uap->req);
	AUDIT_ARG(pid, uap->pid);
	AUDIT_ARG(addr, uap->addr);
	AUDIT_ARG(value32, uap->data);

	if (uap->req == PT_DENY_ATTACH) {
#if (DEVELOPMENT || DEBUG) && !defined(XNU_TARGET_OS_OSX)
		if (PE_i_can_has_debugger(NULL)) {
			return 0;
		}
#endif
		proc_lock(p);
		if (ISSET(p->p_lflag, P_LTRACED)) {
			proc_unlock(p);
			KERNEL_DEBUG_CONSTANT(BSDDBG_CODE(DBG_BSD_PROC, BSD_PROC_FRCEXIT) | DBG_FUNC_NONE,
			    p->p_pid, W_EXITCODE(ENOTSUP, 0), 4, 0, 0);
			exit1(p, W_EXITCODE(ENOTSUP, 0), retval);

			thread_exception_return();
			/* NOTREACHED */
		}
		SET(p->p_lflag, P_LNOATTACH);
		proc_unlock(p);

		return 0;
	}

	if (uap->req == PT_FORCEQUOTA) {
		if (kauth_cred_issuser(kauth_cred_get())) {
			t = current_proc();
			OSBitOrAtomic(P_FORCEQUOTA, &t->p_flag);
			return 0;
		} else {
			return EPERM;
		}
	}

	/*
	 *	Intercept and deal with "please trace me" request.
	 */
	if (uap->req == PT_TRACE_ME) {
retry_trace_me: ;
		proc_t pproc = proc_parent(p);
		if (pproc == NULL) {
			return EINVAL;
		}
#if CONFIG_MACF
		/*
		 * NB: Cannot call kauth_authorize_process(..., KAUTH_PROCESS_CANTRACE, ...)
		 *     since that assumes the process being checked is the current process
		 *     when, in this case, it is the current process's parent.
		 *     Most of the other checks in cantrace() don't apply either.
		 */
		struct proc_ident p_ident = proc_ident(p);
		struct proc_ident pproc_ident = proc_ident(pproc);
		kauth_cred_t pproc_cred = kauth_cred_proc_ref(pproc);

		proc_rele(pproc);
		error = mac_proc_check_debug(&pproc_ident, pproc_cred, &p_ident);
		kauth_cred_unref(&pproc_cred);

		if (error != 0) {
			return error;
		}
		if (proc_find_ident(&pproc_ident) == PROC_NULL) {
			return ESRCH;
		}
#endif
		proc_lock(p);
		/* Make sure the process wasn't re-parented. */
		if (p->p_ppid != pproc->p_pid) {
			proc_unlock(p);
			proc_rele(pproc);
			goto retry_trace_me;
		}
		SET(p->p_lflag, P_LTRACED);
		/* Non-attached case, our tracer is our parent. */
		p->p_oppid = p->p_ppid;
		proc_unlock(p);
		/* Child and parent will have to be able to run modified code. */
		cs_allow_invalid(p);
		cs_allow_invalid(pproc);
		proc_rele(pproc);

		return error;
	}
	if (uap->req == PT_SIGEXC) {
		proc_lock(p);
		if (ISSET(p->p_lflag, P_LTRACED)) {
			SET(p->p_lflag, P_LSIGEXC);
			proc_unlock(p);
			return 0;
		} else {
			proc_unlock(p);
			return EINVAL;
		}
	}

	/*
	 * We do not want ptrace to do anything with kernel or launchd
	 */
	if (uap->pid < 2) {
		return EPERM;
	}

	/*
	 *	Locate victim, and make sure it is traceable.
	 */
	if ((t = proc_find(uap->pid)) == NULL) {
		return ESRCH;
	}

	AUDIT_ARG(process, t);

	task = t->task;
	if (uap->req == PT_ATTACHEXC) {
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wdeprecated-declarations"
		uap->req = PT_ATTACH;
		tr_sigexc = 1;
	}
	if (uap->req == PT_ATTACH) {
#pragma clang diagnostic pop
		int             err;

#if !defined(XNU_TARGET_OS_OSX)
		if (tr_sigexc == 0) {
			error = ENOTSUP;
			goto out;
		}
#endif

		if (kauth_authorize_process(proc_ucred(p), KAUTH_PROCESS_CANTRACE,
		    t, (uintptr_t)&err, 0, 0) == 0) {
			/* it's OK to attach */
			proc_lock(t);
			SET(t->p_lflag, P_LTRACED);
			if (tr_sigexc) {
				SET(t->p_lflag, P_LSIGEXC);
			}

			t->p_oppid = t->p_ppid;
			/* Check whether child and parent are allowed to run modified
			 * code (they'll have to) */
			proc_unlock(t);
			cs_allow_invalid(t);
			cs_allow_invalid(p);
			if (t->p_pptr != p) {
				proc_reparentlocked(t, p, 1, 0);
			}

			proc_lock(t);
			if (get_task_userstop(task) > 0) {
				stopped = 1;
			}
			t->p_xstat = 0;
			proc_unlock(t);
			psignal(t, SIGSTOP);
			/*
			 * If the process was stopped, wake up and run through
			 * issignal() again to properly connect to the tracing
			 * process.
			 */
			if (stopped) {
				task_resume(task);
			}
			error = 0;
			goto out;
		} else {
			error = err;
			if (error == ESRCH) {
				/*
				 * The target 't' is not valid anymore as it
				 * could not be found after the MAC check.
				 */
				return error;
			}
			/* not allowed to attach, proper error code returned by kauth_authorize_process */
			if (ISSET(t->p_lflag, P_LNOATTACH)) {
				psignal(p, SIGSEGV);
			}
			goto out;
		}
	}

	/*
	 * You can't do what you want to the process if:
	 *	(1) It's not being traced at all,
	 */
	proc_lock(t);
	if (!ISSET(t->p_lflag, P_LTRACED)) {
		proc_unlock(t);
		error = EPERM;
		goto out;
	}

	/*
	 *	(2) it's not being traced by _you_, or
	 */
	if (t->p_pptr != p) {
		proc_unlock(t);
		error = EBUSY;
		goto out;
	}

	/*
	 *	(3) it's not currently stopped.
	 */
	if (t->p_stat != SSTOP) {
		proc_unlock(t);
		error = EBUSY;
		goto out;
	}

	/*
	 *	Mach version of ptrace executes request directly here,
	 *	thus simplifying the interaction of ptrace and signals.
	 */
	/* proc lock is held here */
	switch (uap->req) {
	case PT_DETACH:
		if (t->p_oppid != t->p_ppid) {
			struct proc *pp;

			proc_unlock(t);
			pp = proc_find(t->p_oppid);
			if (pp != PROC_NULL) {
				proc_reparentlocked(t, pp, 1, 0);
				proc_rele(pp);
			} else {
				/* original parent exited while traced */
				proc_list_lock();
				t->p_listflag |= P_LIST_DEADPARENT;
				proc_list_unlock();
				proc_reparentlocked(t, initproc, 1, 0);
			}
			proc_lock(t);
		}

		t->p_oppid = 0;
		CLR(t->p_lflag, P_LTRACED);
		CLR(t->p_lflag, P_LSIGEXC);
		proc_unlock(t);
		goto resume;

	case PT_KILL:
		/*
		 *	Tell child process to kill itself after it
		 *	is resumed by adding NSIG to p_cursig. [see issig]
		 */
		proc_unlock(t);
#if CONFIG_MACF
		error = mac_proc_check_signal(p, t, SIGKILL);
		if (0 != error) {
			goto resume;
		}
#endif
		psignal(t, SIGKILL);
		goto resume;

	case PT_STEP:                   /* single step the child */
	case PT_CONTINUE:               /* continue the child */
		proc_unlock(t);
		th_act = (thread_t)get_firstthread(task);
		if (th_act == THREAD_NULL) {
			error = EINVAL;
			goto out;
		}

		/* force use of Mach SPIs (and task_for_pid security checks) to adjust PC */
		if (uap->addr != (user_addr_t)1) {
			error = ENOTSUP;
			goto out;
		}

		if ((unsigned)uap->data >= NSIG) {
			error = EINVAL;
			goto out;
		}

		if (uap->data != 0) {
#if CONFIG_MACF
			error = mac_proc_check_signal(p, t, uap->data);
			if (0 != error) {
				goto out;
			}
#endif
			psignal(t, uap->data);
		}

		if (uap->req == PT_STEP) {
			/*
			 * set trace bit
			 * we use sending SIGSTOP as a comparable security check.
			 */
#if CONFIG_MACF
			error = mac_proc_check_signal(p, t, SIGSTOP);
			if (0 != error) {
				goto out;
			}
#endif
			if (thread_setsinglestep(th_act, 1) != KERN_SUCCESS) {
				error = ENOTSUP;
				goto out;
			}
		} else {
			/*
			 * clear trace bit if on
			 * we use sending SIGCONT as a comparable security check.
			 */
#if CONFIG_MACF
			error = mac_proc_check_signal(p, t, SIGCONT);
			if (0 != error) {
				goto out;
			}
#endif
			if (thread_setsinglestep(th_act, 0) != KERN_SUCCESS) {
				error = ENOTSUP;
				goto out;
			}
		}
resume:
		proc_lock(t);
		t->p_xstat = uap->data;
		t->p_stat = SRUN;
		if (t->sigwait) {
			wakeup((caddr_t)&(t->sigwait));
			proc_unlock(t);
			if ((t->p_lflag & P_LSIGEXC) == 0) {
				task_resume(task);
			}
		} else {
			proc_unlock(t);
		}

		break;

	case PT_THUPDATE:  {
		proc_unlock(t);
		if ((unsigned)uap->data >= NSIG) {
			error = EINVAL;
			goto out;
		}
		th_act = port_name_to_thread(CAST_MACH_PORT_TO_NAME(uap->addr),
		    PORT_TO_THREAD_NONE);
		if (th_act == THREAD_NULL) {
			error = ESRCH;
			goto out;
		}
		ut = (uthread_t)get_bsdthread_info(th_act);
		if (uap->data) {
			ut->uu_siglist |= sigmask(uap->data);
		}
		proc_lock(t);
		t->p_xstat = uap->data;
		t->p_stat = SRUN;
		proc_unlock(t);
		thread_deallocate(th_act);
		error = 0;
	}
	break;
	default:
		proc_unlock(t);
		error = EINVAL;
		goto out;
	}

	error = 0;
out:
	proc_rele(t);
	return error;
}

  • 通过阅读源码发现只需要修改第二个参数的结构体属性uap->req 就可以达到绕过目的 (uap->req == PT_DENY_ATTACH)

定位内核ptrace函数偏移地址

分析第二个参数ptrace_args的内部结构

让我们详细分析 struct ptrace_args 在内存中的布局。在 64 位系统上,考虑到内存对齐和每个成员的大小,下面是详细的内存布局。

假设 pid_t 是 4 字节,user_addr_t 是 8 字节。在 64 位系统上,指针类型通常是 8 字节并且需要对齐到 8 字节边界。

首先,结构体定义如下:

struct ptrace_args {
    int req;         // 4 bytes
    void * unknow[4];        //和实际内存的中偏移不符.实际pid 是+8,所以加了unknow填充
    pid_t pid;       // 4 bytes
    user_addr_t addr;// 8 bytes (on a 64-bit system)
    int data;        // 4 bytes
};

内存布局和对齐分析:

  1. int req:

    • 大小: 4 bytes
    • 对齐: 4 bytes
    • 偏移: 0
    • 结束偏移: 4
  2. pid_t pid:

    • 大小: 4 bytes
    • 对齐: 4 bytes
    • 偏移: 4(紧接在 req 之后)
    • 结束偏移: 8
  3. user_addr_t addr:

    • 大小: 8 bytes
    • 对齐: 8 bytes
    • 由于 addr 需要 8 字节对齐,而当前偏移 8 已经对齐到 8 字节边界,因此无需填充
    • 偏移: 8
    • 结束偏移: 16
  4. int data:

    • 大小: 4 bytes
    • 对齐: 4 bytes
    • 偏移: 16(紧接在 addr 之后)
    • 结束偏移: 20

由于数据对齐要求,编译器可能会在结构体的末尾添加填充以确保结构体大小是对齐的。因此,整个结构体的大小是 24 字节(4 + 4 + 8 + 4 + 4(填充))。

详细内存布局:

+-------------+--------------+--------------+--------------+
| req (4 bytes)               | unknow (4 bytes)           |
+-------------+--------------+--------------+--------------+
| pid (4 bytes)               |     padding (4 bytes)      |
+-------------+--------------+--------------+--------------+
| addr (8 bytes)                                                  |
+-------------+--------------+--------------+--------------+
| data (4 bytes)                | padding (4 bytes)        |
+-------------+--------------+--------------+--------------+

解释:

  • req 占用偏移 0 到 3。
  • unknow 紧接其后,占用偏移 4 到 7。
  • pid 占用偏移 8 到 15。

这就是 struct ptrace_args 在内存中的布局。

编写代码

static int (*ptrace_orig)(struct proc *p, struct ptrace_args *uap, int32_t *retval);

static int my_ptrace(struct proc *p, struct ptrace_args *uap, int32_t *retval){



    kprintf("\n ptrace -- start \n");

    uint8_t cpu = curcpu();
    pid_t caller = caller_pid();

    char *caller_name = unified_kalloc(MAXCOMLEN + 1);

    if(!caller_name){
    kprintf("\n ptrace -- caller_name \n");
        return ptrace_orig(p,uap,retval);
    }
    

    /* proc_name doesn't bzero for some version of iOS 13 */
    _bzero(caller_name, MAXCOMLEN + 1);
    proc_name(caller, caller_name, MAXCOMLEN + 1);

    kprintf("$$$$$$$$$$$$ %s: (CPU %d): '%s' (%d) ptrace_hook  to req : %d pid : %d  \n", __func__, cpu,
            caller_name, caller,uap->req,uap->pid);



    unified_kfree(caller_name);


    if (uap->req == 31 || uap->req == 14)
    {
        /* code */


  
        kprintf("uap->req == 31 uap->req %d \n",uap->req);
        
        kprintf("uap->req == 31 uap->pid %d \n",uap->pid);
        
        kprintf("uap->req == 31 uap->addr %d \n",uap->addr);
        kprintf("uap->req == 31 uap->data %d \n",uap->data);

        
        return 0;
  

    }

        return ptrace_orig(p,uap,retval);
}

    /* iPhone 7 14.1 */                                //FFFFFFF007584D9C                          
    ret = syscall(SYS_xnuspy_ctl, XNUSPY_INSTALL_HOOK, 0xFFFFFFF007584D9C,
            my_ptrace, &ptrace_orig);


完整代码在ptrace_hook

还是拿宇宙最强App 抖音测试下 . 成功!

测试下自己的app

void antiDebug() {
    // ARM syscall to invoke ptrace with PT_DENY_ATTACH
    
    

    
#ifdef __arm64__
        asm volatile(
            "mov x0,#26\n"
            "mov x1,#31\n"
            "mov x2,#0\n"
            "mov x3,#0\n"
            "mov x16,#0\n"
            "svc #128\n"
        );
#endif
    __asm__ volatile(
        "mov x0, #31\n"        // PT_DENY_ATTACH
        "mov x1, #0\n"
        "mov x2, #0\n"
        "mov x3, #0\n"
        "mov x8, #26\n"        // syscall number for ptrace
        "svc #0x80\n"
    );
}

void antiDebug1() {
    
    
  
    typedef int (*ptrace_ptr_t)(int _request, pid_t _pid, caddr_t _addr, int _data);

//    ptrace(PT_DENY_ATTACH, 0, 0, 0);

    void *handle = dlopen(0, RTLD_GLOBAL | RTLD_NOW);
    ptrace_ptr_t ptrace_ptr = (ptrace_ptr_t)dlsym(handle, "ptrace");
    ptrace_ptr(PT_DENY_ATTACH, 0, 0, 0);
}

运行app后也成功hook

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