--- "Chad Leigh -- Shire.Net LLC" <[EMAIL PROTECTED]>

> On Aug 30, 2006, at 12:12 PM, backyard wrote:
> > with HT disabling in FreeBSD is more for the
> security
> > issues about a potential exploit whereby one
> process
> > in one pipe can access the priveledged information
> of
> > a process in another pipe because the two cores
> share
> > one processor cache and thus one cache table. To
> my
> > knowledge this hasn't been exploited yet.
> How is this any different than say an Intel Core Duo
> or Core 2 Duo?   
> I believe they have a shared cache as well for each
> (real) processor  
> core.
> Chad
> ---
> Chad Leigh -- Shire.Net LLC
> Your Web App and Email hosting provider
> chad at shire.net

I would say there is no difference if what you say is
true. A Multi-Core chip is only true SMP if the two
cores share no resources internally and thus are
capable of running process separate from each other
entirely. independantly and with their own internal
caches. The process shouldn't have to wait on a lock
to access it's cache, which I would have to assume
occurs on these HT machines; which is probably why
they have degraded performance. The cache should only
be shared if a process explicity copies its content to
the other cores cache. If should not be possible for
both Cores to see the same internal cache. To my
knowledge the AMDx2 follow this model with independant
cores only sharing a common die. This ensures the
context and priveledge of one running process cannot
be compromised by a non-priveldeged process waiting on
say a login attempt to root, and then grabbing the
password from the common cache before the privelidged
process can clean up.

I don't think this flaw has been exploited yet, but
the boys at OpenBSD found it (from memory, pretty sure
it was one of them) and it has spread through the BSD
community as it has potentially dire consequences.

Personally I'm done with Intel so I don't think I'll
ever have this issue. Afterall they're still the
reason my computer boots up with 640k of RAM... I also
think AMD has come from being a clone to being on top
of the market, but this is my personal opinion. The
fact Core Duos are only 32-bit means Intel is still
only concerned with shortend gains on the Windows
market, not long term migration to 64-bit PCs like
everyone else... And banking on Microsoft has never
been a solid idea; its too bad banks use Windows;
there's a security nightmare, but a topic in and of


freebsd-questions@freebsd.org mailing list
To unsubscribe, send any mail to "[EMAIL PROTECTED]"

Reply via email to