Hi, On Thu, Sep 13, 2012 at 12:29 PM, Kshemendra KP <kshemendra@suphalaam.com> wrote:
In user space when you write beyond your address space (if your write crosses the page boundary alloacted to you), then process is terminated. In the kernel you are still writinng inside the kernel address space. Your write is not beyond kernel address space.
Secondly you are corrupting some other data structure. The kernel stack is part of task_struct of the running process, a kmalloc or slab allocator might have provided this memory (task_-struct). When you write beyond this if the write modiefies some crucial data structure that may result in hang or a crash.
I did a quick calculation on this. The number of slab objects allocated for task_struct in my system are 280 and each size of each object is 3264 ---8<--- root@shubh-VirtualBox:~# cat /proc/slabinfo | grep task_struct task_struct 262 280 3264 10 8 : tunables 0 0 0 : slabdata 28 28 0 ---8<--- So if my understanding is correct, in case if i define an array of more than 280*3264 bytes then it will corrupt the task_struct of at least one significantly important process or at least the task_struct of the process for my terminal will get corrupted?
On Thu, Sep 13, 2012 at 12:15 PM, shubham sharma <shubham20006@gmail.com> wrote:
Hi,
As far as i know, the size of stack allocated in the kernel space is 8Kb for each process. But in case i use more than 8Kb of memory from the stack then what will happen? I think that in that case the system would crash because i am accessing an illegal memory area. I wrote kernel module in which i defined an integer array whose size was 8000. But still it did not crash my system. Why?
The module i wrote was as follows:
#include <linux/kernel.h> #include <linux/module.h>
int __init init_my_module(void) { int arr[8000]; printk("%s:%d\tmodule initilized\n", __func__, __LINE__); arr[1] = 1; arr[4000] = 1; arr[7999] = 1; printk("%s:%d\tarr[1]:%d, arr[4000]:%d, arr[7999]:%d\n", __func__, __LINE__, arr[1], arr[4000], arr[7999]); return 0; }
void __exit cleanup_my_module(void) { printk("exiting\n"); return; }
module_init(init_my_module); module_exit(cleanup_my_module);
MODULE_LICENSE("GPL");
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