From: Robert Hancock <hancockr@shaw.ca>
To: Clemens Kolbitsch <clemens.kol@gmx.at>
Cc: Chris Smith <smitty1elkml@gmail.com>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: Copy large memory regions from & to userspace
Date: Fri, 31 Aug 2007 19:48:12 -0600 [thread overview]
Message-ID: <46D8C4DC.2080307@shaw.ca> (raw)
In-Reply-To: <fa.tMlh7ZYvNMxPEL69Eww8ErwDEmw@ifi.uio.no>
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/
next parent reply other threads:[~2007-09-01 1:53 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <fa.0TqRgC3Smn96vb+Bwv5QRWKBTQg@ifi.uio.no>
[not found] ` <fa.x2L04usZZxVIMYSdrufu+Hen9aY@ifi.uio.no>
[not found] ` <fa.tMlh7ZYvNMxPEL69Eww8ErwDEmw@ifi.uio.no>
2007-09-01 1:48 ` Robert Hancock [this message]
2007-09-01 6:10 ` Copy large memory regions from & to userspace Jan Engelhardt
2007-08-30 22:29 Clemens Kolbitsch
[not found] ` <9b53a56d0708310625q14defcb1l98ab8ce1df2c8fd7@mail.gmail.com>
2007-08-31 13:45 ` Clemens Kolbitsch
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