Re: [PATCH][RFC][0/4] InfiniBand userspace verbs implementation

[Andrew Morton <akpm@osdl.org>]

Timur Tabi <timur.tabi@ammasso.com> wrote:
>
> Andrew Morton wrote:
> 
> > I'm referring to an application which uses your syscalls to obtain pinned
> > memory and uses munlock() so that it may then use your syscalls to obtain
> > evem more pinned memory.  With the objective of taking the machine down.
> 
> I'm in favor of having drivers call do_mlock() and do_munlock() on behalf of the 
> application.  All we need to do is export those functions, and my driver can call them. 
> However, that still doesn't prevent an app from calling munlock().

Precisely.  That's why I suggested that we have an alternative vma->vm_flag
bit which behaves in a similar manner to VM_LOCKED (say, VM_LOCKED_KERNEL),
only userspace cannot alter it.

> But I don't understand the distinction between having the driver call do_mlock() vs. the 
> application calling mlock().  Won't we still have the same problems?  A malicious app can 
> just call our driver instead of calling mlock() or munlock(). The driver won't know the 
> difference between an authorized app and an unauthorized one.

The driver will set VM_LOCKED_KERNEL, not VM_LOCKED.

> Besides, isn't the whole point behind RLIMIT_MEMLOCK to limit how much one process can lock?

Sure.  The internal setting of VM_LOCKED_KERNEL should still use
RLIMIT_MEMLOCK accounting.