Re: Problem with set_memory_rw

Re: Problem with set_memory_rw

[Oleg Kutkov]

"KAMEZAWA Hiroyuki" <kamezawa.hiroyu@jp.fujitsu.com 
<mailto:kamezawa.hiroyu@jp.fujitsu.com>> wrote:
> set_memory_rw()'s 1st argument requires virtual address.
> So, you need virtual address of the page you want.
>
>  - phys_to_virt() ... convert physical address to virtual address.
>  - virt_to_phys() ... convert virtual address to physical.
>
> Anyway, RW is vitual address mapping's attribute and not for physical.
>
> Thanks,
> -Kame   
>

Thank for answer!
But this is a very strange, because 0x0509940, i passed, - it a virtual 
memory address (i got it from System.map, this is a system call table, 
on my machine). set_memory_rw return zero, anyway. So i can't continue 
writing to memory. Maybe, system call table is much write protected, so 
i can't change attribute of memory page?
One more interesting thing:

struct page *pg;
pg = virt_to_page(addr);
unsigned long page_addr;
page_addr = (unsigned long) page_address(pg);


addr - this is my virtual address (provided by System.map)
But page_addr got another value!
What wrong?
Sorry, if my questions is to stupid.

P.S. I know, that overwriting system call table is very bad, i just 
experimenting with my own network drivers and i need to replace some 
network system calls..


Best regard,
Oleg.

Problem with set_memory_rw

[Oleg Kutkov]

Hello, this is my first post in a mailing list, so excuse me if 
something wrong...
I'm new in kernel and try to do some manipulation with memory pages.
For manipulating memory page attributes i used set_memory_rw(),
but function returning 0 and i can't continue writing to memory,
because page, that i want to change, is read only by default.
This is part of my code:


long unsigned addr;

addr = 0x0509940;              //this is addres in memory, that i  want 
to overwrite (read only, for default)

set_memory_rw(addr, 1);    //try to set rw permission on this addres for 
one memory page.


So, function return zero, this is error, as i can understand. If i try 
to write by this address - kernel write in log error messages, such as 
"Unable to handle kernel request at address 0x0509940".
This is kernel bug or something wrong in my code?

Thank for any help.


Best regards,
Oleg.

Re: Problem with set_memory_rw

[KAMEZAWA Hiroyuki]

On Thu, 04 Feb 2010 07:26:25 +0200
Oleg Kutkov <elenbert@gmail.com> wrote:

> Hello, this is my first post in a mailing list, so excuse me if 
> something wrong...
> I'm new in kernel and try to do some manipulation with memory pages.
> For manipulating memory page attributes i used set_memory_rw(),
> but function returning 0 and i can't continue writing to memory,
> because page, that i want to change, is read only by default.
> This is part of my code:
> 
> 
> long unsigned addr;
> 
> addr = 0x0509940;              //this is addres in memory, that i  want 
> to overwrite (read only, for default)
> 
> set_memory_rw(addr, 1);    //try to set rw permission on this addres for 
> one memory page.
> 
> 
> So, function return zero, this is error, as i can understand. If i try 
> to write by this address - kernel write in log error messages, such as 
> "Unable to handle kernel request at address 0x0509940".
> This is kernel bug or something wrong in my code?
> 
> Thank for any help.
> 

set_memory_rw()'s 1st argument requires virtual address.
So, you need virtual address of the page you want.
 
  - phys_to_virt() ... convert physical address to virtual address.
  - virt_to_phys() ... convert virtual address to physical.

Anyway, RW is vitual address mapping's attribute and not for physical.

Thanks,
-Kame