On 28 May 2005 11:08:39 -0000, jhoney jhoney <jhoney_joney@xxxxxxxxxxxxxx> wrote: > > > Hello All, > > Thanks for your explanations.In addition to previous one, > When any process is started, ie after executing the a.out at the linux shell > , It starts executing in the 4GB address space of the process. At that time > it is unable to access the kernel memory. But the moment when it executed > system call which issues a trap , enters in to kernel mode and could access > the kernel memory. Now the module is can access the user space(4GB virtual) > and the kernel memory space also. How this is achieved. This is achieved by setting the addr_limit field of current process, this is done by set_fs() macro, which is defined with following macros in architecture specific uaccess.h file: =================== 28 #define KERNEL_DS MAKE_MM_SEG(0xFFFFFFFFUL) 29 #define USER_DS MAKE_MM_SEG(PAGE_OFFSET) 30 31 #define get_ds() (KERNEL_DS) 32 #define get_fs() (current_thread_info()->addr_limit) 33 #define set_fs(x) (current_thread_info()->addr_limit = (x)) =================== -Gaurav > > > > > On Wed, 25 May 2005 Gaurav Dhiman wrote : > > >On 24 May 2005 05:16:49 -0000, jhoney jhoney > ><jhoney_joney@xxxxxxxxxxxxxx> wrote: > > > > > > > > > Hello All, > > > > > > When application runs ,it can not access the kernel memory but when the > > > module for the corresponding application runs in kernel mode , it has > access > > > to kernel memory. > > > >kernel module is a part of kernel code itself once its loaded into the > >memory, its linked to the kernel core image in memory by insmod. > >kernel module can be used by any process running in user space by > >making a specific system call which might lead the control of > >execution to module code. > > > >-gd > > > > > > > > My question is what made to access the kernel memory module which could > not > > > be done by an application. > > > > > > Regards > > > > > > Jhoney > > > > > > > > > > > > > > > >-- > >Kernelnewbies: Help each other learn about the Linux kernel. > >Archive: http://mail.nl.linux.org/kernelnewbies/ > >FAQ: http://kernelnewbies.org/faq/ > > > > > > > -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
