lkml.org 
[lkml]   [2007]   [Aug]   [31]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: Copy large memory regions from & to userspace
Clemens Kolbitsch wrote:
> On Friday 31 August 2007 15:25:40 you wrote:
>> On 8/30/07, Clemens Kolbitsch <clemens.kol@gmx.at> wrote:
>>> Hi!
>>> Just a short question: What is the correct method of copying large areas
>>> of memory from userspace into userspace when running in kernel-mode?
>> relayfs?
>
> no... I'm copying user-memory to user-memory, not kernel-to-user, however
> running the code in kernel-mode.
>
> what i wanted to know is how to check the access-rights...
> i didn't get any other answers, so for now i'm just using
>
> if (access_ok(VERIFY_READ, from, PAGE_SIZE) &&
> access_ok(VERIFY_WRITE, to, PAGE_SIZE))
> {
> memcpy(to, from, PAGE_SIZE);
> }
>
> and hope that this is the *correct* way to do it...

No, it's not. access_ok does not guarantee that the memory region can be
validly read or written. It only allows using __copy_to_user or
__copy_from_user which skips the same checks that access_ok does.

I'm not aware of any code in the kernel that does userspace-to-userspace
copies directly. Likely because there's rarely a need for it?

--
Robert Hancock Saskatoon, SK, Canada
To email, remove "nospam" from hancockr@nospamshaw.ca
Home Page: http://www.roberthancock.com/

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2007-09-01 03:57    [W:0.027 / U:0.480 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site