Why system call need to copy the date from the userspace before using it

Tomko
2005-04-13T04:25:29Z

Hi all,

I am new to linux , hope someone can help me.
While i am reading the source code of the linux system call , i find
that the system call need to call copy_from_user() to copy the data from
user space to kernel space before using it . Why not use it directly as
the system call has got the address ? Furthermore , how to distinguish
between user space and kernel space ?

Thx a lot,

TOM