Linux 内核:系统调用挂钩示例 [英] Linux Kernel: System call hooking example

问题描述

我正在尝试编写一些简单的测试代码作为挂钩系统调用表的演示.

I'm trying to write some simple test code as a demonstration of hooking the system call table.

"sys_call_table" 在 2.6 中不再导出，所以我只是从 System.map 文件中抓取地址，我可以看到它是正确的(在我找到的地址处查看内存，我可以看到指向系统调用的指针).

"sys_call_table" is no longer exported in 2.6, so I'm just grabbing the address from the System.map file, and I can see it is correct (Looking through the memory at the address I found, I can see the pointers to the system calls).

然而，当我尝试修改这个表时，内核给出了一个糟糕"和无法在虚拟地址 c061e4f4 处理内核分页请求"并且机器重新启动.

However, when I try to modify this table, the kernel gives an "Oops" with "unable to handle kernel paging request at virtual address c061e4f4" and the machine reboots.

这是运行 2.6.18-164.10.1.el5 的 CentOS 5.4.是否有某种保护或我只是有一个错误?我知道它与 SELinux 一起提供，并且我尝试将其置于许可模式，但没有任何区别

This is CentOS 5.4 running 2.6.18-164.10.1.el5. Is there some sort of protection or do I just have a bug? I know it comes with SELinux, and I've tried putting it in to permissive mode, but it doesn't make a difference

这是我的代码:

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/unistd.h>

void **sys_call_table;

asmlinkage int (*original_call) (const char*, int, int);

asmlinkage int our_sys_open(const char* file, int flags, int mode)
{
   printk("A file was opened
");
   return original_call(file, flags, mode);
}

int init_module()
{
    // sys_call_table address in System.map
    sys_call_table = (void*)0xc061e4e0;
    original_call = sys_call_table[__NR_open];

    // Hook: Crashes here
    sys_call_table[__NR_open] = our_sys_open;
}

void cleanup_module()
{
   // Restore the original call
   sys_call_table[__NR_open] = original_call;
}

推荐答案

我终于自己找到了答案.

I finally found the answer myself.

http://www.linuxforums.org/论坛/linux-kernel/133982-cannot-modify-sys_call_table.html

内核在某个时候发生了变化，因此系统调用表是只读的.

The kernel was changed at some point so that the system call table is read only.

密码朋克:

即使迟到了，但解决方案其他人也可能感兴趣:在您将找到 entry.S 文件:代码:

Even if it is late but the Solution may interest others too: In the entry.S file you will find: Code:

.section .rodata,"a"
#include "syscall_table_32.S"

sys_call_table -> ReadOnly 你必须如果你想编译内核新使用 sys_call_table 来破解"...

sys_call_table -> ReadOnly You have to compile the Kernel new if you want to "hack" around with sys_call_table...

该链接还有一个将内存更改为可写的示例.

The link also has an example of changing the memory to be writable.

nasekomoe:

大家好.感谢您的回复.一世很久以前解决了这个问题修改对内存页的访问.一世已经实现了两个功能它用于我的上层代码:

Hi everybody. Thanks for replies. I solved the problem long ago by modifying access to memory pages. I have implemented two functions that do it for my upper level code:

#include <asm/cacheflush.h>
#ifdef KERN_2_6_24
#include <asm/semaphore.h>
int set_page_rw(long unsigned int _addr)
{
    struct page *pg;
    pgprot_t prot;
    pg = virt_to_page(_addr);
    prot.pgprot = VM_READ | VM_WRITE;
    return change_page_attr(pg, 1, prot);
}

int set_page_ro(long unsigned int _addr)
{
    struct page *pg;
    pgprot_t prot;
    pg = virt_to_page(_addr);
    prot.pgprot = VM_READ;
    return change_page_attr(pg, 1, prot);
}

#else
#include <linux/semaphore.h>
int set_page_rw(long unsigned int _addr)
{
    return set_memory_rw(_addr, 1);
}

int set_page_ro(long unsigned int _addr)
{
    return set_memory_ro(_addr, 1);
}

#endif // KERN_2_6_24

这是对我有用的原始代码的修改版本.

Here's a modified version of the original code that works for me.

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/unistd.h>
#include <asm/semaphore.h>
#include <asm/cacheflush.h>

void **sys_call_table;

asmlinkage int (*original_call) (const char*, int, int);

asmlinkage int our_sys_open(const char* file, int flags, int mode)
{
   printk("A file was opened
");
   return original_call(file, flags, mode);
}

int set_page_rw(long unsigned int _addr)
{
   struct page *pg;
   pgprot_t prot;
   pg = virt_to_page(_addr);
   prot.pgprot = VM_READ | VM_WRITE;
   return change_page_attr(pg, 1, prot);
}

int init_module()
{
    // sys_call_table address in System.map
    sys_call_table = (void*)0xc061e4e0;
    original_call = sys_call_table[__NR_open];

    set_page_rw(sys_call_table);
    sys_call_table[__NR_open] = our_sys_open;
}

void cleanup_module()
{
   // Restore the original call
   sys_call_table[__NR_open] = original_call;
}

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