Re: [RFC] syscalls, x86: Add __NR_kcmp syscall

[Cyrill Gorcunov <gorcunov@gmail.com>]

On Wed, Jan 18, 2012 at 03:29:50PM -0800, Eric W. Biederman wrote:
> >
> > It doesn't matter. Even if we take a list of objects the kernel either
> > should return us some ordering info or find duplicates, in any case it
> > makes things more complex i think. So we wanted to bring some minimum
> > into kernel leaving the rest of work to user-space.
> 
> Agreed a syscall does the duplication is probably not the way to go.
> 
>  A syscall that takes a huge list of objects would solve any security
> concerns that we have with returning the object order to user space if
> done carefully, but it would require a bunch of additional user space
> and kernel memory.
> 

yes, an it increase syscall time itself since we will have to provide
this memory dynamically

> Sometimes taking a data structure transforming it into a weird form for
> a specific task and then transforming the data structure back to it's
> original form is a useful way to go.  So I think a general kernel object
> deduplicating system call is an interesting plan B, but a straight
> comparison function if we can make it work is a lot more flexible and
> useful.
> 

I hope the root-only restriction would resolve the potential security
problem, since as I mentioned if I've hijacked the machine and already
goot root -- mem order is not that interesting info I could obtain from
such computer :)

	Cyrill