Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Zenbleed

lock.cmpxchg8b.com

Post reply on HN
Print view View original

171–180 of 378 posts

Re: Zenbleed

#171

Post by zamadatix »

jeroenhd wrote: post #161
astrange wrote: post #104

Earlier quoted context omitted.

Are people running multiple untrusted VMs without turning SMT off? Even letting them share caches seems like asking for trouble.

Not only do people do this, it's generally how VPS providers work. Most machines barely use the CPU most of the time (web servers etc.) so reserving a full CPU core for a VPS is horribly inefficient. It doesn't matter anyway, because SMT isn't relevant for this particular bug. With SMT allowing twice the cores on a CPU for most workloads, disabling it would double the cost for most providers! There are VPS providers…

SMT is relevant in the VM case of this bug because it determines whether this bug is restricted to data outside the VM or not.

Providers usually won't disable SMT completely, they'd run a scheduler which only allows 1 VM to use both SMT threads of a core. Ultra cheap VPS providers may still find that not worth the pennies though as if you sell a majority of single core VPS then the majority of your SMT threads are still unavailable even with the scheduler approach.

Fully dedicated cores aren't necessarily required because in the timesliced case the registers are unloaded and reloaded when different VMs are shuffled on and off the core. That said, they definitely prevent the cross-vm-data-leak case of this bug.

Re: Zenbleed

#172

Post by byvirtueof »

eindiran wrote: post #131
jahsome wrote: post #125

Earlier quoted context omitted.

I'm not sure five year olds know what microcode is. I'm 35, been in tech nearly 20 years and don't recall having heard that specific term before today.

The whole "explain like I'm 5" thing is ridiculous. A huge percentage of topics simply cannot be broken down to an average 5 year old in a way that makes the conversation worth having at all. The 5 year old has no context about why in recent years there has been a huge push towards running your own code on other people's computers using various isolation techniques, or why people are trying to exploit that. The 5 yea…

I agree that many topics are hard to explain to a five year old, but ELI5 can be very helpful in forcing people to simplify their writing. Many people explain things in an unnecessarily complex way, and ELI5 at least makes them think about the target audience.

Re: Zenbleed

#173

Post by wbl »

artisanspam wrote: post #81
wbl wrote: post #77

Earlier quoted context omitted.

Because the context switch only affects architectural state not microarchitectural state.

Yes I understand that but I was struggling to think of a sequence of instructions that would cause this secret leaking on a single thread. But a simple example is `vzeroupper` followed by anything that writes a secret to the same register file entry would be leaked on a subsequent flush.

That's not quite right. The attacker doss the vzeroupper rollback. Any registers in the physical file that haven't been overwritten can be exposed as a result, regardless of what the victim did.

Re: Zenbleed

#175

Post by dtx1 »

Night_Thastus wrote: post #168
dtx1 wrote: post #9

Earlier quoted context omitted.

From my experience: Better have a > 32gig USB Flash drive, everything else doesn't work (MSI) and I don't have an UPS so it's always quite an exciting experience. Especially since Motherboard Manifactures save almost a whole dollar by not having a display ouputting anything. So it's blinkenlights and hope for the best

Get a UPS!! Not just for convenience, but safety. You don't want to be caught out when something goes wrong, even without flashing the bios. A lot of boards these days have 7-segment displays. They're not great, but they're a good step up. Don't need to spend a lot, I think they show up on $300-ish boards. Mine definitely does.

I see no need for it. Living in Germany, any kind of power outages are exceptionally rare. I remember one in the last 10 years for a few hours and that was very local. If I am in a situation where a power outage occurs, i'll listen to my battery radio for a while and be fine. I work on nothing and rely on nothing that would actually require a UPS.

Re: Zenbleed

#176

Post by zokier »

cesarb wrote: post #167
brazzledazzle wrote: post #150

Earlier quoted context omitted.

I do not miss performance tuning apache.

In my personal experience, the first step in tuning Apache was "put a nginx server in front of it". Running out of workers (either processes in the prefork model, or threads otherwise) was in my experience way too easy, especially when keepalive is enabled (even a couple of seconds of keepalive can be painful). The async model used by nginx can handle a lot more connections before running out of resources.

Apache has been defaulting to event mpm for over a decade.

Re: Zenbleed

#177

Post by AdmiralAsshat »

FirmwareBurner wrote: post #156
darkwater wrote: post #148

Earlier quoted context omitted.

I think the interesting point here might be one could be able to extract some secret from memory of a PS5, like to break some kind of encryption

What valuable secrets do people have on their PS5/Xbox? You also need a way to deploy the malicious payload on those platforms which, due to their closed nature, is very difficult to do.

At least with the PS3, I seem to recall that I couldn't extract any of my games' save data from the hard-drive of my PS3 unit that went dead due to RROD (or was it YLOD?) because the hard-drive was encrypted using the PS3's serial key as part of the encryption.

I don't know if that mechanism persists into the PS4/PS5.

Re: Zenbleed

#178

Post by Night_Thastus »

dtx1 wrote: post #175
Night_Thastus wrote: post #168

Earlier quoted context omitted.

Get a UPS!! Not just for convenience, but safety. You don't want to be caught out when something goes wrong, even without flashing the bios. A lot of boards these days have 7-segment displays. They're not great, but they're a good step up. Don't need to spend a lot, I think they show up on $300-ish boards. Mine definitely does.

I see no need for it. Living in Germany, any kind of power outages are exceptionally rare. I remember one in the last 10 years for a few hours and that was very local. If I am in a situation where a power outage occurs, i'll listen to my battery radio for a while and be fine. I work on nothing and rely on nothing that would actually require a UPS.

It's like not having a backup drive. Everything is fine until one day it isn't.

A good UPS does more than just protect from outages. It also protects from surges and low-voltage situations that can both damage the equipment severely.

A UPS doesn't cost much and will last many years. Buying a new motherboard and GPU because they got fried is much more expensive.

Re: Zenbleed

#179

Post by Night_Thastus »

formerly_proven wrote: post #76
ls612 wrote: post #36

Earlier quoted context omitted.

My new computer takes a while to POST (z690 with ddr5 smh) so it’s basically been continuously either on or in sleep since I built it 18 months ago and I’ve had an unexpected shutdown due to power loss once in that time according to the Event log. I think the risk of losing power while flashing the bios is very small in real life unless you are stuck in a place with third world electricity infrastructure.

If POST takes a long time it’s often memory training, backing off on the timings just slightly might make it go a lot quicker. Bios updates also often twiddle knobs in this area.

Doesn't that only happen on the first boot with new memory? As well, I thought it was more of a concern on AMD, and less on Intel. (Z690 is Intel)
Post reply on HN