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Kali Linux(内核版本5)上的系统调用挂钩

本文介绍了Kali Linux(内核版本5)上的系统调用挂钩的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

限时删除！！

我正在尝试为Kali Linux 2021-W1(Linux内核版本5)上的bind()系统调用设置挂钩，但由于某种原因，调用原始系统调用失败并出现错误。

以下是我的代码：

/* includes, license, author... */

void **sys_call_table_addr = (void **) 0xffffffff9e0002c0;

int enable_page_rw(void *ptr){
        unsigned int level;
        pte_t *pte = lookup_address((unsigned long) ptr, &level);
        if(pte->pte &~_PAGE_RW){
            pte->pte |=_PAGE_RW;
        }
        return 0;
}

int disable_page_rw(void *ptr){
        unsigned int level;
        pte_t *pte = lookup_address((unsigned long) ptr, &level);
        pte->pte = pte->pte &~_PAGE_RW;
        return 0;
}

asmlinkage int (*original_bind) (int, const struct sockaddr *, int);
asmlinkage int log_bind(int sockfd, const struct sockaddr *addr, int addrlen) {
        int ret;
        printk(KERN_INFO SOCKETLOG "bind was called");
        return (*original_bind)(sockfd, addr, addrlen);
}

static int __init socketlog_init(void) {
        printk(KERN_INFO SOCKETLOG "socketlog module has been loaded
");

        enable_page_rw(sys_call_table_addr);
        original_bind = sys_call_table_addr[__NR_bind];
        if (!original_bind) return -1;
        sys_call_table_addr[__NR_bind] = log_bind;
        disable_page_rw(sys_call_table_addr);

        printk(KERN_INFO SOCKETLOG "original_bind = %p", original_bind);
        return 0;
}

static void __exit socketlog_exit(void) {
        printk(KERN_INFO SOCKETLOG "socketlog module has been unloaded
");

        enable_page_rw(sys_call_table_addr);
        sys_call_table_addr[__NR_bind] = original_bind;
        disable_page_rw(sys_call_table_addr);
}

module_init(socketlog_init);
module_exit(socketlog_exit);

执行sudo insmod socketlog.ko后，可以看到预期的输出：

[  +0.000488] [SOCKETLOG] socketlog module has been loaded
[  +0.000002] [SOCKETLOG] original_bind = 00000000bbf288f1

但每次调用bind()时，我都会得到奇怪的行为：

[  +0.000488] [SOCKETLOG] bind was called
[  +0.000005] BUG: unable to handle page fault for address: 0000000040697fb8
[  +0.000002] #PF: supervisor read access in kernel mode
[  +0.000001] #PF: error_code(0x0000) - not-present page

不出所料0x0000000040697fb8是0x00000000bbf288f1指向的地址：原始系统调用的内容。我错过了什么？

推荐答案

可能您包装系统调用的方式不起作用。例如，在Linux 5.4.0-59通用x86_64体系结构上，内核中的系统调用通过名为do_syscall_64()的公共包装器进行调用。它通过pt_regs结构将参数传递到sys_call_table[]：

中的条目
__visible void do_syscall_64(unsigned long nr, struct pt_regs *regs)
{
    struct thread_info *ti;

    enter_from_user_mode();
    local_irq_enable();
    ti = current_thread_info();
    if (READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY)
        nr = syscall_trace_enter(regs);

    if (likely(nr < NR_syscalls)) {
        nr = array_index_nospec(nr, NR_syscalls);
        regs->ax = sys_call_table[nr](regs); <-------- Call to the entry with pt_regs structure
#ifdef CONFIG_X86_X32_ABI
    } else if (likely((nr & __X32_SYSCALL_BIT) &&
              (nr & ~__X32_SYSCALL_BIT) < X32_NR_syscalls)) {
        nr = array_index_nospec(nr & ~__X32_SYSCALL_BIT,
                    X32_NR_syscalls);
        regs->ax = x32_sys_call_table[nr](regs);
#endif
    }

    syscall_return_slowpath(regs);
}

pt_regs结构嵌入用户传递给系统调用的参数。因此，这可能解释了您崩溃的原因：printk(...；绑定被调用)之所以工作，是因为它不访问参数，但在对原始系统调用条目的调用不符合预期参数之后。

如果您查看net/socket.c中的Bind()系统调用的源代码，它的定义为：

SYSCALL_DEFINE3(bind, int, fd, struct sockaddr __user *, umyaddr, int, addrlen)
{
    return __sys_bind(fd, umyaddr, addrlen);
}

上面的宏SYSCALL_DEFINE3()展开为一些包装，用于从pt_regs结构中提取参数。

因此，这里是一个例子，在我的5.4.0-60通用Ubuntu x86_64上运行的模块中的一些修复：

#include <linux/version.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <asm/ptrace.h>
#include <linux/socket.h>
#include <linux/kallsyms.h>


MODULE_LICENSE("Dual BSD/GPL");

typedef int (* syscall_wrapper)(struct pt_regs *);

unsigned long sys_call_table_addr;

#define SOCKETLOG "[SOCKETLOG]"


int enable_page_rw(void *ptr){
  unsigned int level;
  pte_t *pte = lookup_address((unsigned long) ptr, &level);
  if(pte->pte &~_PAGE_RW){
    pte->pte |=_PAGE_RW;
  }
  return 0;
}

int disable_page_rw(void *ptr){
  unsigned int level;
  pte_t *pte = lookup_address((unsigned long) ptr, &level);
  pte->pte = pte->pte &~_PAGE_RW;
  return 0;
}

syscall_wrapper original_bind;

//asmlinkage int log_bind(int sockfd, const struct sockaddr *addr, int addrlen) {
int log_bind(struct pt_regs *regs) {
  printk(KERN_INFO SOCKETLOG "bind was called");
  return (*original_bind)(regs);
}

static int __init socketlog_init(void) {

  printk(KERN_INFO SOCKETLOG "socketlog module has been loaded
");

  sys_call_table_addr = kallsyms_lookup_name("sys_call_table");

  printk(KERN_INFO SOCKETLOG "sys_call_table@%lx
", sys_call_table_addr);

  enable_page_rw((void *)sys_call_table_addr);
  original_bind = ((syscall_wrapper *)sys_call_table_addr)[__NR_bind];
  if (!original_bind) return -1;
  ((syscall_wrapper *)sys_call_table_addr)[__NR_bind] = log_bind;
  disable_page_rw((void *)sys_call_table_addr);

  printk(KERN_INFO SOCKETLOG "original_bind = %p", original_bind);
  return 0;
}

static void __exit socketlog_exit(void) {
  printk(KERN_INFO SOCKETLOG "socketlog module has been unloaded
");

  enable_page_rw((void *)sys_call_table_addr);
  ((syscall_wrapper *)sys_call_table_addr)[__NR_bind] = original_bind;
  disable_page_rw((void *)sys_call_table_addr);
}

module_init(socketlog_init);
module_exit(socketlog_exit);

带测试：

$ sudo insmod ./bind_ovl.ko
$ dmesg
[ 2253.201888] [SOCKETLOG]socketlog module has been loaded
[ 2253.209486] [SOCKETLOG]sys_call_table@ffffffff88c013a0
[ 2253.209489] [SOCKETLOG]original_bind = 00000000f54304a9

例如，在重新加载网页后，我得到：

$ dmesg
[ 2136.946042] [SOCKETLOG]socketlog module has been unloaded
[ 2253.201888] [SOCKETLOG]socketlog module has been loaded
[ 2253.209486] [SOCKETLOG]sys_call_table@ffffffff88c013a0
[ 2253.209489] [SOCKETLOG]original_bind = 00000000f54304a9
[ 2281.716581] [SOCKETLOG]bind was called
[ 2295.607476] [SOCKETLOG]bind was called
[ 2301.947866] [SOCKETLOG]bind was called
[ 2304.088116] [SOCKETLOG]bind was called
[ 2309.599634] [SOCKETLOG]bind was called
[ 2310.946833] [SOCKETLOG]bind was called

卸载模块后：

$ sudo rmmod bind_ovl
$ dmesg
[...]
[ 2390.908456] [SOCKETLOG]bind was called
[ 2398.921475] [SOCKETLOG]bind was called
[ 2398.928855] [SOCKETLOG]socketlog module has been unloaded
当然，您可以通过显示传递给系统调用的参数来增强重载。在x86_64上，系统调用最多通过处理器寄存器传递6个参数。我们可以在pt_regs结构中检索它们。后者在Arch/x86/Include/ASM/ptrace.h中定义为：

struct pt_regs {
/*
 * C ABI says these regs are callee-preserved. They aren't saved on kernel entry
 * unless syscall needs a complete, fully filled "struct pt_regs".
 */
    unsigned long r15;
    unsigned long r14;
    unsigned long r13;
    unsigned long r12;
    unsigned long bp;
    unsigned long bx;
/* These regs are callee-clobbered. Always saved on kernel entry. */
    unsigned long r11;
    unsigned long r10;
    unsigned long r9;
    unsigned long r8;
    unsigned long ax;
    unsigned long cx;
    unsigned long dx;
    unsigned long si;
    unsigned long di;
/*
 * On syscall entry, this is syscall#. On CPU exception, this is error code.
 * On hw interrupt, it's IRQ number:
 */
    unsigned long orig_ax;
/* Return frame for iretq */
    unsigned long ip;
    unsigned long cs;
    unsigned long flags;
    unsigned long sp;
    unsigned long ss;
/* top of stack page */
};

系统调用的参数传递约定为：参数#0到参数#5分别传递到RDI、rsi、RDX、r10、r8和r9寄存器。

根据此规则，对于Bind()系统调用，参数位于以下寄存器中：

  • rdi=int(套接字描述符)
  • rsi=struct sockaddr*addr
  • rdx=socklen_t addrlen

然后您可以使用如下内容来增强日志功能：

int log_bind(struct pt_regs *regs) {
  printk(KERN_INFO SOCKETLOG "bind was called(%d, %p, %u)", (int)(regs->di), (void *)(regs->si), (unsigned int)(regs->dx));
  return (*original_bind)(regs);
}

模块中的跟踪信息变得更加详细：

[ 3259.589915] [SOCKETLOG]socketlog module has been loaded
[ 3259.594631] [SOCKETLOG]sys_call_table@ffffffff88c013a0
[ 3259.594634] [SOCKETLOG]original_bind = 00000000f54304a9
[ 3274.368906] [SOCKETLOG]bind was called(149, 0000000091c163d5, 12)
[ 3276.040330] [SOCKETLOG]bind was called(149, 0000000075b17cb4, 12)
[ 3278.203942] [SOCKETLOG]bind was called(188, 0000000091c163d5, 12)
[ 3287.014980] [SOCKETLOG]bind was called(214, 0000000075b17cb4, 12)
[ 3287.021167] [SOCKETLOG]bind was called(214, 0000000091c163d5, 12)
[ 3298.395713] [SOCKETLOG]bind was called(3, 000000008c2a9103, 12)
[ 3298.403249] [SOCKETLOG]socketlog module has been unloaded

这篇关于Kali Linux(内核版本5)上的系统调用挂钩的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！

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