Re: slab.c use of __get_user and sparse

[Al Viro <viro@parcelfarce.linux.theplanet.co.uk>]

On Sat, Jan 15, 2005 at 11:01:51PM +0100, Andi Kleen wrote:
> > Based on the comment it is understood that suddenly this pointer points
> > to userspace, because the module got unloaded.
> > I wonder why we can rely on the same address now the module got unloaded -
> > we may risk this virtual address is taken over by someone else?
> 
> The address is not user space; you would be lying.
> 
> Perhaps it's best to get rid of the hack completely. Turn kmem_cache_t->name
> into an array and copy the name instead of storing the pointer, then
> it wouldn't be needed at all.

Alternatively, we could provide a new primitive -

size_t safe_memcpy(void *to, void *from, size_t size);

Semantics: copy byte-by-byte until we either get 'size' bytes or trigger an
exception.  Return the number of bytes copied.

Obvious implementation via __get_user() would be default, overridable by
architecture...