bug-hurd
[Top][All Lists]
Advanced

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: client-side memory buffers


From: Neal H. Walfield
Subject: Re: client-side memory buffers
Date: Tue, 01 Apr 2008 10:28:14 +0200
User-agent: Wanderlust/2.14.0 (Africa) SEMI/1.14.6 (Maruoka) FLIM/1.14.8 (Shij┼Ź) APEL/10.6 Emacs/21.4 (i486-pc-linux-gnu) MULE/5.0 (SAKAKI)

At Mon, 31 Mar 2008 21:23:41 -0600,
Joshua Stratton wrote:
> 
> I was on the irc channel talking about the feasibility using client-side
> memory buffers for a new network stack.  Based on some feedback about
> difficulties of implementing this in the Hurd, I thought I would ask anyone
> if they thought this would be especially difficult--particularly Marcus and
> Neal.

The way to do client side allocations is to have the client pass a
memory object to the server.  There is a problem with this approach,
however, as it allows the client to interfere with the server's
operations.

The problem is exactly the same as that with L4's data spaces.  When
the server maps and accesses the memory object, the client can revoke
the mapping at any time (via memory_object_lock_request), causing the
server to fault.  If you manage to unmap the memory while the server
is blocked on it (waiting for it to be paged in) and has a lock,
you've successfully created a denial of service.

Without changing the Mach interfaces, the best approach is to have the
server allocate the memory and to transfer it to the client using the
normal Mach buffer passing semantics.

Neal





reply via email to

[Prev in Thread] Current Thread [Next in Thread]