Project 1 - HackMD

# Project 1 ### 組員名單 * 110525015 劉松靄 * 111525013 何雋永 * 109502547 楊晴方 ### 系統環境 * 作業系統： ubuntu 18.04 * Kernel 版本： 5.4.0-131-generic ### 新增 syscall 過程由於篇幅較多，因此另外寫了一篇，在[這裡](https://hackmd.io/7x2suD5FRPuoavelhqUP4Q)。 ### 其他兩個 project [project 2](https://hackmd.io/4Ax7oedqSFyVfvgI04PiZQ) [project 3](https://hackmd.io/TStjhzZwTtqv82RHsfUJVg) ### kernel space code ``` #include <linux/init.h> #include <linux/kernel.h> #include <linux/module.h> #include <linux/sched.h> #include <linux/mm.h> #include <linux/syscalls.h> #include <linux/uaccess.h> int segNum = 6; int *data[20]; char* segmentName[6] = {"BSS", "Text", "Data", "Heap", "Stack", "Shared library"}; void printVMA(struct task_struct *task){ struct mm_struct *mm = task->mm; struct vm_area_struct *vma; int count = 0, index = 0; printk("\nText Segment start = 0x%lx, end = 0x%lx\n" "\nData Segment start = 0x%lx, end = 0x%lx\n" "\nStack Segment start = 0x%lx\n" "\nHeap Segment start = 0x%lx, end = 0x%lx\n", mm->start_code, mm->end_code, mm->start_data, mm->end_data, mm->start_stack, mm->start_brk, mm->brk); for(; index < segNum; index++){ count = 0; for(vma = mm->mmap; vma; vma = vma->vm_next){ ++count; if(data[index] >= vma->vm_start && data[index] <= vma->vm_end){ printk("\n%s Segment is in vma %d\n", segmentName[index], count); printk("\nStarts at 0x%lx, Ends at 0x%lx\n", vma->vm_start, vma->vm_end); } } } } void convertToPhysical(struct task_struct *task){ pgd_t *pgd; p4d_t *p4d; pud_t *pud; pmd_t *pmd; pte_t *pte; unsigned long paddr=0, page_addr=0, page_offset=0; int index=0; for(; index<segNum; index++){ pgd = pgd_offset(task->mm, data[index]); if(pgd_none(*pgd)){ printk("not mapped in pgd\n"); return; } p4d = p4d_offset(pgd, data[index]); if(p4d_none(*p4d)){ printk("not mapped in p4d\n"); return; } pud = pud_offset(p4d, data[index]); if(pud_none(*pud)){ printk("not mapped in pud\n"); return; } pmd = pmd_offset(pud, data[index]); if(pmd_none(*pmd)){ printk("not mapped in pmd\n"); return; } pte = pte_offset_kernel(pmd, data[index]); if(pte_none(*pte)){ printk("not mapped in pte\n"); return; } page_addr = pte_val(*pte) & PAGE_MASK; page_offset = (unsigned long)data[index] & ~PAGE_MASK; paddr = page_addr | page_offset; printk("\nphysical address %s Segment is 0x%lx\n", segmentName[index], paddr); } } SYSCALL_DEFINE2(printSegment, int, pid, const int*, userData){ copy_from_user(data, userData, sizeof(data)); printk("\ntask id is %d\n", current->pid); convertToPhysical(current); printVMA(current); return 0; } ``` ### user space code ``` #include <stdio.h> #include <stdlib.h> #include <sys/syscall.h> #include <linux/kernel.h> #include <pthread.h> #include <unistd.h> int initData = 1, cnt = 0; int notInitData; int *userData[20]; void* t1(){ int a = 1; int *p = malloc(sizeof(int)); *p = 1; cnt = 0; userData[cnt++] = &notInitData; userData[cnt++] = t1; userData[cnt++] = &initData; userData[cnt++] = p; userData[cnt++] = &a; userData[cnt++] = printf; syscall(336, (int)syscall(SYS_gettid), userData); pthread_exit(NULL); } void* t2(){ int a = 1; int *p = malloc(sizeof(int)); *p = 1; cnt = 0; userData[cnt++] = &notInitData; userData[cnt++] = t2; userData[cnt++] = &initData; userData[cnt++] = p; userData[cnt++] = &a; userData[cnt++] = printf; syscall(336, (int)syscall(SYS_gettid), userData); pthread_exit(NULL); } int main(){ printf("%d\n", initData); pthread_t thread1, thread2; int a = 1; int *p = malloc(sizeof(int)); *p = 1; userData[cnt++] = &notInitData; userData[cnt++] = main; userData[cnt++] = &initData; userData[cnt++] = p; userData[cnt++] = &a; userData[cnt++] = printf; syscall(336, (int)syscall(SYS_gettid), userData); pthread_create(&thread1, NULL, t1, NULL); pthread_join(thread1, NULL); pthread_create(&thread2, NULL, t2, NULL); pthread_join(thread2, NULL); // syscall(337); return 0; } ``` ### kernel 輸出結果 **main thread** ``` [ 236.564583] task id is 2430 [ 236.564593] physical address BSS Segment is 0x800000016a9d8040 [ 236.564598] physical address Text Segment is 0x178bf5b20 [ 236.564601] physical address Data Segment is 0x800000016a9d8010 [ 236.564604] physical address Heap Segment is 0x8000000179153670 [ 236.564607] physical address Stack Segment is 0x800000018cf6604c [ 236.564610] physical address Shared library Segment is 0x1105e6e40 [ 236.564613] Text Segment start = 0x55abd9a00000, end = 0x55abd9a00f18 Data Segment start = 0x55abd9c01d78, end = 0x55abd9c02014 Stack Segment start = 0x7fff1861a150 Heap Segment start = 0x55abda33d000, end = 0x55abda35e000 [ 236.564621] BSS Segment is in vma 3 [ 236.564623] Starts at 0x55abd9c02000, Ends at 0x55abd9c03000 [ 236.564628] Text Segment is in vma 1 [ 236.564630] Starts at 0x55abd9a00000, Ends at 0x55abd9a01000 [ 236.564633] Data Segment is in vma 3 [ 236.564635] Starts at 0x55abd9c02000, Ends at 0x55abd9c03000 [ 236.564638] Heap Segment is in vma 4 [ 236.564640] Starts at 0x55abda33d000, Ends at 0x55abda35e000 [ 236.564643] Stack Segment is in vma 20 [ 236.564646] Starts at 0x7fff185fb000, Ends at 0x7fff1861c000 [ 236.564648] Shared library Segment is in vma 5 [ 236.564651] Starts at 0x7f3bd3400000, Ends at 0x7f3bd35e7000 ``` **thread 1** ``` [ 236.564856] task id is 2431 [ 236.564864] physical address BSS Segment is 0x800000016a9d8040 [ 236.564869] physical address Text Segment is 0x178bf585a [ 236.564873] physical address Data Segment is 0x800000016a9d8010 [ 236.564875] physical address Heap Segment is 0x8000000178ffab20 [ 236.564878] physical address Stack Segment is 0x8000000179162edc [ 236.564882] physical address Shared library Segment is 0x1105e6e40 [ 236.564885] Text Segment start = 0x55abd9a00000, end = 0x55abd9a00f18 Data Segment start = 0x55abd9c01d78, end = 0x55abd9c02014 Stack Segment start = 0x7fff1861a150 Heap Segment start = 0x55abda33d000, end = 0x55abda35e000 [ 236.564892] BSS Segment is in vma 3 [ 236.564896] Starts at 0x55abd9c02000, Ends at 0x55abd9c03000 [ 236.564901] Text Segment is in vma 1 [ 236.564904] Starts at 0x55abd9a00000, Ends at 0x55abd9a01000 [ 236.564907] Data Segment is in vma 3 [ 236.564910] Starts at 0x55abd9c02000, Ends at 0x55abd9c03000 [ 236.564913] Heap Segment is in vma 5 [ 236.564915] Starts at 0x7f3bcc000000, Ends at 0x7f3bcc021000 [ 236.564919] Stack Segment is in vma 8 [ 236.564922] Starts at 0x7f3bd2c00000, Ends at 0x7f3bd3400000 [ 236.564925] Shared library Segment is in vma 9 [ 236.564928] Starts at 0x7f3bd3400000, Ends at 0x7f3bd35e7000 ``` **thread 2** ``` [ 236.565424] task id is 2432 [ 236.565432] physical address BSS Segment is 0x800000016a9d8040 [ 236.565437] physical address Text Segment is 0x178bf59bd [ 236.565440] physical address Data Segment is 0x800000016a9d8010 [ 236.565443] physical address Heap Segment is 0x8000000179ae8220 [ 236.565445] physical address Stack Segment is 0x8000000179162edc [ 236.565448] physical address Shared library Segment is 0x1105e6e40 [ 236.565451] Text Segment start = 0x55abd9a00000, end = 0x55abd9a00f18 Data Segment start = 0x55abd9c01d78, end = 0x55abd9c02014 Stack Segment start = 0x7fff1861a150 Heap Segment start = 0x55abda33d000, end = 0x55abda35e000 [ 236.565459] BSS Segment is in vma 3 [ 236.565462] Starts at 0x55abd9c02000, Ends at 0x55abd9c03000 [ 236.565467] Text Segment is in vma 1 [ 236.565469] Starts at 0x55abd9a00000, Ends at 0x55abd9a01000 [ 236.565472] Data Segment is in vma 3 [ 236.565475] Starts at 0x55abd9c02000, Ends at 0x55abd9c03000 [ 236.565478] Heap Segment is in vma 5 [ 236.565480] Starts at 0x7f3bcc000000, Ends at 0x7f3bcc021000 [ 236.565483] Stack Segment is in vma 12 [ 236.565485] Starts at 0x7f3bd2c00000, Ends at 0x7f3bd3400000 [ 236.565488] Shared library Segment is in vma 13 [ 236.565491] Starts at 0x7f3bd3400000, Ends at 0x7f3bd35e7000 ``` ### 記憶體 layout ![](https://i.imgur.com/ug44NIh.png) ### 補充的知識點 #### 1. pgdir_shift, pgd_offset ``` #define pgd_offset(mm, address) pgd_offset_pgd((mm)->pgd, (address)) static inline pgd_t *pgd_offset_pgd(pgd_t *pgd, unsigned long address) { return (pgd + pgd_index(address)); }; #define pgd_index(a) (((a) >> PGDIR_SHIFT) & (PTRS_PER_PGD - 1)) ``` ![](https://i.imgur.com/5ucWfFJ.png) ![](https://i.imgur.com/VBjDlT3.png) #### 2. syscall_define 做了哪些事 ``` #define SYSCALL_DEFINE1(name, ...) SYSCALL_DEFINEx(1, _##name, __VA_ARGS__) #define SYSCALL_DEFINE2(name, ...) SYSCALL_DEFINEx(2, _##name, __VA_ARGS__) #define SYSCALL_DEFINE3(name, ...) SYSCALL_DEFINEx(3, _##name, __VA_ARGS__) #define SYSCALL_DEFINE4(name, ...) SYSCALL_DEFINEx(4, _##name, __VA_ARGS__) #define SYSCALL_DEFINE5(name, ...) SYSCALL_DEFINEx(5, _##name, __VA_ARGS__) #define SYSCALL_DEFINE6(name, ...) SYSCALL_DEFINEx(6, _##name, __VA_ARGS__) ``` ``` #define SYSCALL_DEFINEx(x, sname, ...) \ SYSCALL_METADATA(sname, x, __VA_ARGS__) \ __SYSCALL_DEFINEx(x, sname, __VA_ARGS__) SYSCALL_METADATA 有點看不懂，而且覺得不是重點，所以先略過 ``` ``` #define __SYSCALL_DEFINEx(x, name, ...) \ __diag_push(); \ __diag_ignore(GCC, 8, "-Wattribute-alias", \ "Type aliasing is used to sanitize syscall arguments");\ asmlinkage long sys##name(__MAP(x,__SC_DECL,__VA_ARGS__)) \ __attribute__((alias(__stringify(__se_sys##name)))); \ ALLOW_ERROR_INJECTION(sys##name, ERRNO); \ static inline long __do_sys##name(__MAP(x,__SC_DECL,__VA_ARGS__));\ asmlinkage long __se_sys##name(__MAP(x,__SC_LONG,__VA_ARGS__)); \ asmlinkage long __se_sys##name(__MAP(x,__SC_LONG,__VA_ARGS__)) \ { \ long ret = __do_sys##name(__MAP(x,__SC_CAST,__VA_ARGS__));\ __MAP(x,__SC_TEST,__VA_ARGS__); \ __PROTECT(x, ret,__MAP(x,__SC_ARGS,__VA_ARGS__)); \ return ret; \ } \ __diag_pop(); \ static inline long __do_sys##name(__MAP(x,__SC_DECL,__VA_ARGS__)) ``` ``` asmlinkage long sys##name(__MAP(x,__SC_DECL,__VA_ARGS__)) \ __attribute__((alias(__stringify(__se_sys##name)))); 例子 : asmlinkage long sys##_hello(__MAP(1, __SC_DECL, int, a)) __MAP(1, __SC_DECL, int, a) => __MAP1(__SC_DECL, int, a) => __SC_DECL(int, a) => int a asmlinkage long sys##_hello(__MAP(1, __SC_DECL, int, a)) => asmlinkage long sys_hello(int, a) ## 為連接符號 alias 讓它等價於 __se_sys_hello ``` ``` asmlinkage long __se_sys##name(__MAP(x,__SC_LONG,__VA_ARGS__)); 跟上面的 asmlinkage long sys##name 轉換類似唯一的差別是 __SC_LONG #define __SC_LONG(t, a) __typeof(__builtin_choose_expr(__TYPE_IS_LL(t), 0LL, 0L)) a 在 32 bit 系統上比較有意義，因為 64 bit 中 LL 與 L 都是 8 bytes asmlinkage long __se_sys##_hello(__MAP(1,__SC_LONG,int, a)); => asmlinkage long __se_sys_hello(long a); 重點 : 將輸入擴展成 64 bit ``` ``` asmlinkage long __se_sys##name(__MAP(x,__SC_LONG,__VA_ARGS__)) \ { \ long ret = __do_sys##name(__MAP(x,__SC_CAST,__VA_ARGS__)); \ __MAP(x,__SC_TEST,__VA_ARGS__); \ __PROTECT(x, ret,__MAP(x,__SC_ARGS,__VA_ARGS__)); \ return ret; \ } #define __SC_CAST(t, a) (__force t) a 直接把它當作強制型態轉換就好 => __SC_CAST(int, a) == (int) a long ret = __do_sys##_hello(__MAP(1,__SC_CAST, int, a)); => asmlinkage long __do_sys_hello((int) a); ``` 總而言之，就是將輸入強制轉換到 long，然後再轉回 int，也就是 syscall 一開始傳入的型別。至於為甚麼要多做這些事，跟 [CVE-2009-2009](https://nvd.nist.gov/vuln/detail/CVE-2009-2009) 有關。 #### 3. current current 定義在 <asm/current.h> 中 ``` #ifndef _ASM_X86_CURRENT_H #define _ASM_X86_CURRENT_H #include <linux/compiler.h> #include <asm/percpu.h> #ifndef __ASSEMBLY__ struct task_struct; DECLARE_PER_CPU(struct task_struct *, current_task); static __always_inline struct task_struct *get_current(void) { return this_cpu_read_stable(current_task); } #define current get_current() #endif /* __ASSEMBLY__ */ #endif /* _ASM_X86_CURRENT_H */ ``` 可以看到 currrent 變數是一個指向 struct task_struct 的指標 ### reference [https://www.jabperf.com/5-level-vs-4-level-page-tables-does-it-matter/](https://www.jabperf.com/5-level-vs-4-level-page-tables-does-it-matter/) [https://www.cnblogs.com/muahao/p/10297852.html](https://www.cnblogs.com/muahao/p/10297852.html) [https://elixir.bootlin.com/linux/v6.0.6/](https://elixir.bootlin.com/linux/v6.0.6/)

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