copy_to_user to a kmapped address

copy_to_user to a kmapped address

[Jeff Dike]

Is this (in file_read_actor) bogus or am I missing something?

1621            kaddr = kmap(page);
1622            left = __copy_to_user(desc->buf, kaddr + offset, size);
1623            kunmap(page);

It seems to me that copy_to_user should be able to assume that the destination
address is a user address.

This is biting me because I'm moving the UML kernel into a separate address
space, so there's no way, in general, to tell the difference between a kernel
address and a userspace address.

				Jeff

Re: copy_to_user to a kmapped address

[Russell King]

On Mon, Aug 26, 2002 at 04:19:37PM -0500, Jeff Dike wrote:
> Is this (in file_read_actor) bogus or am I missing something?
> 
> 1621            kaddr = kmap(page);
> 1622            left = __copy_to_user(desc->buf, kaddr + offset, size);
> 1623            kunmap(page);
> 
> It seems to me that copy_to_user should be able to assume that the destination
> address is a user address.
> 
> This is biting me because I'm moving the UML kernel into a separate address
> space, so there's no way, in general, to tell the difference between a kernel
> address and a userspace address.

Umm, that's copying from kaddr + offset _to_ desc->buf.  desc->buf
should be the user space address, and kaddr + offset a kernel address:

unsigned long __copy_to_user(void *to, const void *from, unsigned long n)

-- 
Russell King (rmk@arm.linux.org.uk)                The developer of ARM Linux
             http://www.arm.linux.org.uk/personal/aboutme.html

Re: copy_to_user to a kmapped address

[Jeff Dike]

rmk@arm.linux.org.uk said:
> Umm, that's copying from kaddr + offset _to_ desc->buf.  desc->buf
> should be the user space address, and kaddr + offset a kernel address:

Duh, nevermind...

				Jeff