All processes have the same stack_canary? In the Linux kernel, `stack_canary` is the one of the stack protection mechanisms. This value is generated by `boot_init_stack_canary()`. (`/init/main.c`) `boot_init_stack_canary()` randomly generates `stack_canary` from `get_random_bytes()`. And this canary value is referenced into task structure(`struct task`) and save in the `gs` segment register. When a process is generated, the process gets `stack_canary` from `gs` segment. If `stack_canary` is not refreshed anymore, all processes have the same `stack_canary` value? Otherwise, are there any different generation methods?

The stack canary is initialised with a random value any time a task struct is duplicated; see `dup_task_struct()` in `kernel/fork.c` (and in particular line 380 in version 4.7). So each forked process gets a random canary, which means there's a _very_ high probability that each process has a different canary (and more importantly, you can't predict another process's stack canary).

`boot_init_stack_canary()` ensures that the first "task" (the kernel) has a stack canary. That canary isn't re-used for processes.