On Feb 23, 2007, at 4:40 PM, Jeff Dike wrote:
> On Fri, Feb 23, 2007 at 01:36:12PM -0500, Bryan Parno wrote:
>> I'm interested in mediating accesses by the UML guest kernel to
>> memory used by the UML guest processes. At present, I'm looking at a
>> scenario using SKAS3, so the kernel has an address space distinct
>> from that of the user processes. I guess I'm a bit confused as to
>> how the guest kernel actually manages to touch guest process memory
>> (e.g., for copying system call arguments). Looking through /arch/um/
>> kernel/skas/uaccess.c, it appears that all of these accesses devolve
>> to performing a strncpy or memcpy, but I don't see a translation from
>> an address in the user's address space to one in the kernel's address
>> space. Does this happen somewhere else, or am I misunderstanding
>> SKAS?
>
> So far, you're fine. What you're missing is, i.e.:
>
> int copy_from_user_skas(void *to, const void __user *from, int n)
> {
> if(segment_eq(get_fs(), KERNEL_DS)){
> memcpy(to, (__force void*)from, n);
> return(0);
> }
>
> return(access_ok(VERIFY_READ, from, n) ?
> buffer_op((unsigned long) from, n, 0, copy_chunk_from_user,
> &to):
> n);
> }
>
> The buffer_op case handles userspace memory. It does the following:
> figures out where in kernel physical memory the userspace data is
> breaks the operation across pages if necessary
> wraps enough state around the operation to be able to handle
> page faults and finish it after the page has been faulted in
>
> Jeff
>
> --
> Work email - jdike at linux dot intel dot com
>
Cool, thanks for the pointer.
Bryan
-------------------------------------------------------------------------
Take Surveys. Earn Cash. Influence the Future of IT
Join SourceForge.net's Techsay panel and you'll get the chance to share your
opinions on IT & business topics through brief surveys-and earn cash
http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV
_______________________________________________
User-mode-linux-devel mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/user-mode-linux-devel
