# 2021q3 Homework1 (quiz1) contributed by <`fwfly`> 程式編譯後會出現 kallsyms_lookup_name undefine error ```cpp 2021_summer_q1$ make make -C /lib/modules/`uname -r`/build M=/home/fwfly/project/2021_summer_q1 modules make[1]: Entering directory '/usr/src/linux-headers-5.8.0-59-generic' CC [M] main.o LD [M] hideproc.o MODPOST Module.symvers ERROR: modpost: "kallsyms_lookup_name" [hideproc.ko] undefined! make[2]: *** [scripts/Makefile.modpost:111: Module.symvers] Error 1 make[2]: *** Deleting file 'Module.symvers' make[1]: *** [Makefile:1698: modules] Error 2 make[1]: Leaving directory '/usr/src/linux-headers-5.8.0-59-generic' make: *** [Makefile:9: all] Error 2 ``` 這個 https://github.com/h33p/kallsyms-mod 提供一個 livepatch 來處理 undefined 問題 ## 使用 livepatch 先 copy 必要檔案到當前目錄 ``` #cp kallsyms.c kallsyms.h kallsyms_kp.c kallsyms_lp.c ksyms.h <測驗一目錄> ``` 更改 main.c 檔案 include 的部分 ```cpp #include <linux/list.h> #include <linux/module.h> #include <linux/proc_fs.h> #include "kallsyms.h" // 新增 livepatch #include "ksyms.h" // 新增 livepatch MODULE_LICENSE("GPL"); MODULE_AUTHOR("National Cheng Kung University, Taiwan"); ... KSYMDEF(kvm_lock); // 新增 livepatch KSYMDEF(vm_list); // 新增 livepatch static int _hideproc_init(void) { int err, dev_major; /* 以下為新增的 livepatch 部分 */ int r; if ((r = init_kallsyms())) return r; KSYMINIT_FAULT(kvm_lock); KSYMINIT_FAULT(vm_list); /* 到這裡為止 */ dev_t dev; ... ... ``` 更改 Makefile 來 compile livepatch 檔案 ```cpp MODULENAME := hideproc obj-m += $(MODULENAME).o $(MODULENAME)-y += main.o kallsyms.o //新增 kallsyms.o ... ``` 完整修改可以看這個部分 https://github.com/fwfly/2021_summer_q1/commit/1546cbf845d0d96c7a2f183b152034abef15153d ## 如果遇到 _hideproc_init crash 雖然 ko 檔 build 成功，但是執行時卻至 print 一個 killed ``` $ sudo insmod hideproc.ko Killed ``` 如果用 `dmsg` 則會發現 module crash ``` [34345.866304] hideproc: loading out-of-tree module taints kernel. [34345.866409] hideproc: module verification failed: signature and/or required key missing - tainting kernel [34345.867707] @ _hideproc_init [34345.867930] BUG: kernel NULL pointer dereference, address: 0000000000000000 [34345.867938] #PF: supervisor instruction fetch in kernel mode [34345.867941] #PF: error_code(0x0010) - not-present page [34345.867944] PGD 0 P4D 0 [34345.867952] Oops: 0010 [#1] SMP NOPTI [34345.867961] CPU: 2 PID: 9801 Comm: insmod Tainted: G OE 5.8.0-59-generic #66~20.04.1-Ubuntu [ 182.857782] Hardware name: HP HP EliteBook 745 G3/807E, BIOS N73 Ver. 01.20 10/03/2017 [ 182.857785] RIP: 0010:0x0 [ 182.857789] Code: Unable to access opcode bytes at RIP 0xffffffffffffffd6. [ 182.857791] RSP: 0018:ffffb46f8215fc30 EFLAGS: 00010246 [ 182.857793] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000 [ 182.857795] RDX: 0000000000000000 RSI: ffff8db5f5862688 RDI: ffffffffc1139206 [ 182.857796] RBP: ffffb46f8215fc38 R08: 0000000000000000 R09: ffffb46f8215f9b8 [ 182.857797] R10: ffff8db6752b7bff R11: 0000000000000000 R12: 000000000ed00001 [ 182.857799] R13: ffff8db576676b60 R14: 0000000000000000 R15: ffffb46f8215fe70 [ 182.857801] FS: 00007efcfa7dd540(0000) GS:ffff8db5faf80000(0000) knlGS:0000000000000000 [ 182.857803] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 182.857804] CR2: ffffffffffffffd6 CR3: 0000000131592000 CR4: 00000000001406e0 [ 182.857806] Call Trace: [ 182.857812] kallsyms_lookup_name+0x15/0x20 [hideproc] [ 182.857817] _hideproc_init+0xc6/0x1bd [hideproc] [ 182.857820] ? device_read.cold+0x18/0x18 [hideproc] [ 182.857826] do_one_initcall+0x4a/0x200 [ 182.857829] ? kfree+0x231/0x250 [ 182.857836] ? _cond_resched+0x19/0x30 [ 182.857838] ? kmem_cache_alloc_trace+0x177/0x240 [ 182.857843] do_init_module+0x62/0x250 [ 182.857846] load_module+0x1185/0x1390 [ 182.857850] ? ima_post_read_file+0x108/0x120 [ 182.857854] __do_sys_finit_module+0xc9/0x130 [ 182.857857] ? __do_sys_finit_module+0xc9/0x130 [ 182.857860] __x64_sys_finit_module+0x1a/0x20 [ 182.857865] do_syscall_64+0x49/0xc0 [ 182.857868] entry_SYSCALL_64_after_hwframe+0x44/0xa9 [ 182.857871] RIP: 0033:0x7efcfa3e389d ... ``` 往下看 call stack 可以看到問題是在 kallsyms_lookup_name ``` [ 182.857812] kallsyms_lookup_name+0x15/0x20 [hideproc] [ 182.857817] _hideproc_init+0xc6/0x1bd [hideproc] ``` 而其實問題是出在沒有把 init_kallsyms 的程式碼放上去(更先前的版本)，修改後 insmod 就確認可以安裝上去 新增部分 ```cpp KSYMDEF(kvm_lock); // 新增 livepatch KSYMDEF(vm_list); // 新增 livepatch static int _hideproc_init(void) { int err, dev_major; /* 以下為新增的 livepatch 部分 */ int r; if ((r = init_kallsyms())) return r; KSYMINIT_FAULT(kvm_lock); KSYMINIT_FAULT(vm_list); /* 到這裡為止 */ ``` ### kallsyms-compat 嘗試的把 kallsyms patch 的 function 改成 static inline 放到 kallsysms-compact.h 裡面． 但是編譯卻會得到以下錯誤 ```cpp $ make make -C /lib/modules/`uname -r`/build M=/home/fwfly/project/kallsyms-compat modules make[1]: Entering directory '/usr/src/linux-headers-5.8.0-63-generic' CC [M] /home/fwfly/project/kallsyms-compat/main.o In file included from /home/fwfly/project/kallsyms-compat/main.c:1: /home/fwfly/project/kallsyms-compat/kallasys-compat.h:91:29: error: static declaration of ‘kallsyms_lookup_name’ follows non-static declaration 91 | static inline unsigned long kallsyms_lookup_name(const char *name) | ^~~~~~~~~~~~~~~~~~~~ In file included from ./include/linux/ftrace.h:11, from ./include/linux/livepatch.h:13, from /home/fwfly/project/kallsyms-compat/kallasys-compat.h:59, from /home/fwfly/project/kallsyms-compat/main.c:1: ./include/linux/kallsyms.h:76:15: note: previous declaration of ‘kallsyms_lookup_name’ was here 76 | unsigned long kallsyms_lookup_name(const char *name); | ^~~~~~~~~~~~~~~~~~~~ ``` > 將上面的 `kallsyms_lookup_name` (inline static 函式) 改為 `__kallsyms_lookup_name`，然後再定義: > ```cpp > #define kallsyms_lookup_name(x) __kallsyms_lookup_name(x) > ``` > :notes: jserv ## Reference * [tools/debugging/kernel-chktaint](https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/plain/tools/debugging/kernel-chktaint) * [Tainted kernels ](https://www.kernel.org/doc/html/v5.8/admin-guide/tainted-kernels.html)