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isc:labs:kernel:tasks:02 [2021/11/25 12:30] radu.mantu |
isc:labs:kernel:tasks:02 [2022/10/08 22:05] (current) radu.mantu [02. [??p] Kernel modules] |
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| Line 6: | Line 6: | ||
| <code bash> | <code bash> | ||
| - | $ lsmod | + | [student@host]$ lsmod |
| ecdh_generic 16384 1 bluetooth | ecdh_generic 16384 1 bluetooth | ||
| - | $ modinfo ecdh_generic | grep description | + | [student@host]$ modinfo ecdh_generic | grep description |
| description: ECDH generic algorithm | description: ECDH generic algorithm | ||
| - | $ modinfo bluetooth | grep description | + | [student@host]$ modinfo bluetooth | grep description |
| description: Bluetooth Core ver 2.22 | description: Bluetooth Core ver 2.22 | ||
| </code> | </code> | ||
| Line 24: | Line 24: | ||
| Now, let's compile our module, upload it into the kernel, and see what happens: | Now, let's compile our module, upload it into the kernel, and see what happens: | ||
| <code bash> | <code bash> | ||
| - | $ make | + | [student@host]$ make |
| - | $ sudo insmod test.ko | + | [student@host]$ sudo insmod test.ko |
| - | $ sudo dmesg | + | [student@host]$ sudo dmesg |
| ... | ... | ||
| [ 6348.461247] my-first-module: Hello world! | [ 6348.461247] my-first-module: Hello world! | ||
| - | $ sudo rmmod test | + | [student@host]$ sudo rmmod test |
| - | $ sudo dmesg | + | [student@host]$ sudo dmesg |
| ... | ... | ||
| [ 6348.461247] my-first-module: Hello world! | [ 6348.461247] my-first-module: Hello world! | ||
| Line 40: | Line 40: | ||
| Here, we used **insmod** to upload a //%%.ko%%// kernel object file into the kernel proper and **rmmod** to remove it. **dmesg** is a tool that prints the kernel message buffer. Note that there are multiple [[https://www.kernel.org/doc/html/latest/core-api/printk-basics.html|log levels]] ranging from **debug** to **emergency**. **pr_info()** is the kernel's **printf()** variant that corresponds to one of the less urgent levels. **dmesg** can be configured to squelch messages under a certain level but depending on how your kernel was compiled, some of the more important messages will also be echoed to your terminal. | Here, we used **insmod** to upload a //%%.ko%%// kernel object file into the kernel proper and **rmmod** to remove it. **dmesg** is a tool that prints the kernel message buffer. Note that there are multiple [[https://www.kernel.org/doc/html/latest/core-api/printk-basics.html|log levels]] ranging from **debug** to **emergency**. **pr_info()** is the kernel's **printf()** variant that corresponds to one of the less urgent levels. **dmesg** can be configured to squelch messages under a certain level but depending on how your kernel was compiled, some of the more important messages will also be echoed to your terminal. | ||
| - | === [??p] Task B - Debugging === | + | === [??p] Task B - Debugging (1) === |
| In this task we are going to add a bug to our initial module. We will do this by applying a [[https://devmanual.gentoo.org/tools-reference/diff-and-patch/index.html|diffpatch]] to our source: | In this task we are going to add a bug to our initial module. We will do this by applying a [[https://devmanual.gentoo.org/tools-reference/diff-and-patch/index.html|diffpatch]] to our source: | ||
| Line 176: | Line 176: | ||
| [root@guest]$ cat /proc/modules | [root@guest]$ cat /proc/modules | ||
| test 20480 1 - Loading 0xffffffffc0304000 (O+) | test 20480 1 - Loading 0xffffffffc0304000 (O+) | ||
| + | </code> | ||
| + | |||
| + | In this case, the best course of action is to simply reboot, but if you want to risk it, just run ''rmmod -f'' to force unloading the module. Be warned that this is very dangerous. Also, if the module is still there after using the ''-f'' flag, make sure that //CONFIG_MODULE_FORCE_UNLOAD// was set at compile time. | ||
| + | |||
| + | <code bash> | ||
| + | # check if force unloading the module is an option | ||
| + | [root@guest]$ zcat /proc/config.gz | grep CONFIG_MODULE_FORCE_UNLOAD | ||
| + | CONFIG_MODULE_FORCE_UNLOAD=y | ||
| + | |||
| + | # force unload the kernel module | ||
| + | [root@guest]$ rmmod -f test | ||
| </code> | </code> | ||
| </note> | </note> | ||
| + | |||
| + | |||
