Hi, Nidhi,
Thanks! Now I know what is the problem.
But in my project, I am developing a virtual char device driver
such that user can read any process's memory contents by specifying
its pid and virtual address. Therefore, a device /dev/gh is
registered, and the user try to do something like:
echo -n targetpid>/dev/gh & echo -n addr>/dev/gh
Therefore, the target process can't be modified. The device driver
will retrieve the value by pid and virtual address and return it to
user at terminal. I don't know how to solve this problem with get_user
under my scenario. Thank you!
Fangkai
On Wed, Apr 28, 2010 at 1:42 AM, nidhi mittal hada
<nidhimittal19@xxxxxxxxx> wrote:
> you should somehow call the kernel module from user space program ...
> may be using ioctl ..
> so that you are in same process context --- as the one you are sending
> address from .
>
> write char dev driver with ioctl method defined
> then call ioctl from user space
>
> ioctl(fd,<IOCTL_CMD>,addrees you want to send)
>
>
> Now in kernel module
>
> get_user(kernel data variable, <user space address>);
>
> Nidhi
>
>
>
>
>
>
>
> On Wed, Apr 28, 2010 at 11:55 AM, Yang Fangkai <wolfgang.yang@xxxxxxxxx>
> wrote:
>>
>> Hi, Nidhi,
>>
>> Thanks for your reply! Yes, you are right. I pass the address
>> to the module from bash command echo, therefore when the address is
>> referred, the current pid is bash's pid, instead of the simple program
>> I wrote.
>>
>> But how can I fix this problem?
>>
>> Thank you!
>>
>> Fangkai
>>
>> On Wed, Apr 28, 2010 at 1:01 AM, nidhi mittal hada
>> <nidhimittal19@xxxxxxxxx> wrote:
>> >
>> > in your kernel module try to print current->pid
>> > is it same as the user space process id ?
>> > i think when in kernel module you are not in the same process context
>> > whihc
>> > you want to refer ...
>> >
>> >
>> > Nidhi
>> >
>> > On Wed, Apr 28, 2010 at 10:38 AM, Yang Fangkai <wolfgang.yang@xxxxxxxxx>
>> > wrote:
>> >>
>> >> Hi, all,
>> >>
>> >> I have a problem with get_user() macro. What I did is as follows:
>> >>
>> >> I run the following program
>> >>
>> >> int main()
>> >> {
>> >> int a = 20;
>> >> printf("address of a: %p", &a);
>> >> sleep(200);
>> >> return 0;
>> >> }
>> >>
>> >> When the program runs, it outputs the address of a, say, 0xbff91914.
>> >>
>> >> Then I pass this address to a module running in Kernel Mode that
>> >> retrieves the contents at this address (at the time when I did this, I
>> >> also made sure the process didn't terminate, because I put it to sleep
>> >> for 200 seconds... ):
>> >>
>> >> The address is firstly sent as a string, and I cast them into pointer
>> >> type.
>> >>
>> >> int * ptr = (int*)simple_strtol(buffer, NULL,16);
>> >> printk("address: %p",ptr); // I use this line to make sure the cast is
>> >> correct. When running, it does output bff91914
>> >> int val = 0;
>> >> int res;
>> >> res= get_user(val, (int*) ptr);
>> >>
>> >> However, res is always not 0, meaning that get_user returns error. I
>> >> am wondering what is the problem....
>> >>
>> >> Thank you!!
>> >>
>> >> --
>> >> To unsubscribe from this list: send an email with
>> >> "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx
>> >> Please read the FAQ at http://kernelnewbies.org/FAQ
>> >>
>> >
>> >
>> >
>> > --
>> > Thanks & Regards
>> > Nidhi Mittal Hada
>> > Scientific officer D
>> > Computer Division
>> > Bhabha Atomic Research Center
>> > Mumbai
>> >
>> >
>> >
>
>
>
> --
> Thanks & Regards
> Nidhi Mittal Hada
> Scientific officer D
> Computer Division
> Bhabha Atomic Research Center
> Mumbai
>
>
>
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