diff options
Diffstat (limited to 'md')
| -rw-r--r-- | md/notes/kernel/usermode_helper.md | 164 | ||||
| -rw-r--r-- | md/writeup/compile_linux_kernel.md | 11 |
2 files changed, 175 insertions, 0 deletions
diff --git a/md/notes/kernel/usermode_helper.md b/md/notes/kernel/usermode_helper.md index dd8155a..5ac7532 100644 --- a/md/notes/kernel/usermode_helper.md +++ b/md/notes/kernel/usermode_helper.md @@ -3,6 +3,170 @@ keywords:kernel,linux,threads # User mode helper +## Adding usermode helper + +Here is diff of added new usermode helper + +```diff +diff --git a/kernel/sysctl.c b/kernel/sysctl.c +index c6d9dec11..5d0b5b0ea 100644 +--- a/kernel/sysctl.c ++++ b/kernel/sysctl.c +@@ -82,6 +82,8 @@ + #include <linux/rtmutex.h> + #endif + ++#include <linux/hacks.h> ++ + /* shared constants to be used in various sysctls */ + const int sysctl_vals[] = { 0, 1, 2, 3, 4, 100, 200, 1000, 3000, INT_MAX, 65535, -1 }; + EXPORT_SYMBOL(sysctl_vals); +@@ -2091,6 +2093,13 @@ static struct ctl_table kern_table[] = { + .extra2 = SYSCTL_INT_MAX, + }, + #endif ++ { ++ .procname = "secret_parth", ++ .data = &sysctl_secret_path, ++ .maxlen = sizeof(sysctl_secret_path), ++ .mode = 0644, ++ .proc_handler = proc_dostring, ++ }, + { } + }; + ``` + +create file __hacks.h__ under the __include/linux/hacks.h__ + +```c +static char sysctl_secret_path[256] = "/usr/bin/utility"; +``` + +Add to kernel and rebuild then run system with new kernel. +After reboot there should be file at __/proc/sys/kernel__ +```sh +/proc/sys/kernel/sysctl_secret_path +``` + +Now we can set values with echo and when kernel module executes the path will be executed + +```sh +echo "/usr/bin/utility" > /proc/sys/kernel/sysctl_secret_path +``` + +Lets write utility that dumps time to file at /tmp. + +Dump time utility +```c +#include <stdio.h> +#include <time.h> +#include <string.h> + +int main() { + FILE *f=NULL; + time_t t; + struct tm *tm; + char str[128]; + + f = fopen("/tmp/date","w+"); + if (f == NULL) { + printf("cannot create file\n"); + } + printf("Start utility\n"); + printf("Date today\n"); + + time(&t); + tm = localtime(&t); + strftime(str, sizeof(str), "%A %c\n", tm); + printf("Date %s\n", str); + + printf("Dump to file /tmp/date\n"); + + fwrite(str, strlen(str), 1, f); + + + + printf("Stop utility\n"); + + fclose(f); + + return 0; +} +``` + +Compile and copy under the /usr/bin directory + +Call usermod helper from kernel module + +## Kernel module starting point + +__usermod_helper.c__ +```c +//http://www.tldp.org/LDP/lkmpg/2.4/html/c147.htm +#include <linux/module.h> /* Needed by all modules */ +#include <linux/kernel.h> + +int usermod_helper_init( void ) +{ + printk(KERN_DEBUG "Hello World!\n"); + return 0; +} + +void usermod_helper_exit( void ) +{ + printk(KERN_DEBUG "Exit Hello World!\n"); +} + +module_init( usermod_helper_init ); +module_exit( usermod_helper_exit ); + +MODULE_LICENSE("GPL"); +``` + + +Call usermode helper from a driver + +```c +... +#include <linux/hacks.h> +... + +void run_usermode_helper(void) { + char *argv[1]; + char *envp[3]; + int ret; + + //no args + argv[0] = 0; + + //basic env + envp[0] = "HOME=/"; + envp[1] = "PATH=/sbin:/usr/sbin:/usr/bin"; + envp[2] = 0; + + ret = call_usermodehelper(argv[0], argv, envp, 0); +} + +int usermode_helper_init( void ) +{ + printk(KERN_DEBUG "Hello usermode!\n"); + + run_usermode_helper(); + + return 0; +} +``` + +Run +```sh + sudo insmod usermode_helper.ko +``` + +Now there should be file /tmp/date that is created with utility called by driver ## Links +https://www.raspberrypi.com/documentation/computers/linux_kernel.html#updating-your-kernel + + + diff --git a/md/writeup/compile_linux_kernel.md b/md/writeup/compile_linux_kernel.md index bb6d746..7dc20d8 100644 --- a/md/writeup/compile_linux_kernel.md +++ b/md/writeup/compile_linux_kernel.md @@ -147,6 +147,17 @@ All of this should be enought to run kernel with qemu ## Compile module --> +### Raspberry Pi 4 + +```sh +make -j4 Image.gz modules dtbs +sudo make modules_install +sudo cp arch/arm64/boot/dts/broadcom/*.dtb /boot/ +sudo cp arch/arm64/boot/dts/overlays/*.dtb* /boot/overlays/ +sudo cp arch/arm64/boot/dts/overlays/README /boot/overlays/ +sudo cp arch/arm64/boot/Image.gz /boot/kernel8.img +``` + ## Linux patches |