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New cloud attack takes full control of virtual machines with little effort

arstechnica.com

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Re: New cloud attack takes full control of virtual machines with little effort

#91

Post by nickpsecurity »

marcosdumay wrote: post #90
willvarfar wrote: post #52

Earlier quoted context omitted.

Encrypted RAM is offered by the newest Intel server-grade CPUs (SGX, Skylake) and the next AMD server-grade CPUs (SME, Zen). One of the main use-cases for these technologies is trusted computing in a cloud environment - the customer can assert that the hardware is securing the program state from the eyes of the computer owner!. However, the cloud is actually made from cheap commodity boxes without server-grade anythi…

> However, the cloud is actually made from cheap commodity boxes without server-grade anything! ;) You know, I refuse to buy anything that does not support ECC for my home desktops (and don't even pay much for it). Only my laptop got a pass from this because there was literally no option available with it. Good to know cloud providers are not as careful... But honestly, shouldn't be a surprise.

Same here. It helps to sell it if you don't say ECC = RAM + extra cash. That's the normal method. I instead say you have two options:

1. RAM that works at this price.

2. RAM that allows more crashes or corruption of your files for slightly-lower price.

The Right Thing suddenly looks more obvious except to cheap skates. Now I just need one with ChipKill built-in. That's the next level of ECC. I haven't heard whether Intel or AMD got something similar.

Re: New cloud attack takes full control of virtual machines with little effort

#92

Post by frostmatthew »

runeks wrote: post #48
frostmatthew wrote: post #3

This attack wouldn't work with [current versions] of ESXi since VMs now share pages only if the salt value and contents of the pages are identical (each VM uses a unique salt by default). https://kb.vmware.com/selfservice/microsites/search.do?langu...

How can VMs share a memory page at all with this scheme when the salt is unique to each VM? It sounds more like turning off inter-VM memory sharing...

Each VM has a unique salt by default, but you can still specify two or more VMs to share a salt. See also the comment[1] below by xavierd.

[1] https://news.ycombinator.com/item?id=12411146

Re: New cloud attack takes full control of virtual machines with little effort

#94

Post by amluto »

willvarfar wrote: post #52
nickpsecurity wrote: post #15

Earlier quoted context omitted.

There's CPU's that do memory, integrity checking to contain attacks. They're designed for stoping software and peripheral attacks mainly but consider RAM untrusted. They could probably be modified to deal with the new attacks.

Encrypted RAM is offered by the newest Intel server-grade CPUs (SGX, Skylake) and the next AMD server-grade CPUs (SME, Zen). One of the main use-cases for these technologies is trusted computing in a cloud environment - the customer can assert that the hardware is securing the program state from the eyes of the computer owner!. However, the cloud is actually made from cheap commodity boxes without server-grade anythi…

Encrypted RAM as AMD is implementing it (SME) protects nicely from "cold-boot attacks" but is otherwise largely a feel-good feature. It also probably doesn't help a whole lot against rowhammer-style attacks because it's merely encrypted, not authenticated. The result is that a bit flip will effectively randomize 64 bytes or whatever the block size is but will not be otherwise detected by the hardware. I bet that clever attackers will find a nice way to take over by randomizing 64 bytes.

Intel's encrypted RAM is authenticated quite nicely, but it's not (yet?) designed for general purpose use -- it's for SGX only right now. Using it for everything would (if I understand correctly) add considerable space overhead and possibly considerable latency.

Re: New cloud attack takes full control of virtual machines with little effort

#95

Post by willvarfar »

amluto wrote: post #94
willvarfar wrote: post #52

Earlier quoted context omitted.

Encrypted RAM is offered by the newest Intel server-grade CPUs (SGX, Skylake) and the next AMD server-grade CPUs (SME, Zen). One of the main use-cases for these technologies is trusted computing in a cloud environment - the customer can assert that the hardware is securing the program state from the eyes of the computer owner!. However, the cloud is actually made from cheap commodity boxes without server-grade anythi…

Encrypted RAM as AMD is implementing it (SME) protects nicely from "cold-boot attacks" but is otherwise largely a feel-good feature. It also probably doesn't help a whole lot against rowhammer-style attacks because it's merely encrypted, not authenticated. The result is that a bit flip will effectively randomize 64 bytes or whatever the block size is but will not be otherwise detected by the hardware. I bet that clev…

But encryption will prevent dedupe meaning a vm cannot attack other occupants as described in the article.

Re: New cloud attack takes full control of virtual machines with little effort

#96

Post by mankash666 »

userbinator wrote: post #14

The rowhammer "attack" is successful only because the hardware is just plain broken , and I consider it in the same category as things like a CPU which will calculate 1+1=3 if the computation of 1+1 is done enough times --- nothing software should even try to fix, because the problem is at a lower level. The solution is to demand that the hardware manufacturers make memory which actually works like memory should; and…

This blame placed on HW stems from a lack of understanding of RAM physics/electronics. As dimensions scale down, these things happen.

The market has chosen to adopt the cost benefits of smaller transistors and higher capacity for the same $. It's a mix of physics and market forces, not malfunctioning hardware.

Re: New cloud attack takes full control of virtual machines with little effort

#97

Post by Dylan16807 »

acobster wrote: post #79
Dylan16807 wrote: post #60

Earlier quoted context omitted.

Rowhammer is largely random. You don't get to target specific bits of physical ram. You find scarce weak bits and work to get the data located there. In this case that means you can only pick a couple bits per 4KB to attack. That won't let you fake out a CRC.

That's where I'm getting a little hazy. The paper says the attacker can "induce bit flips over arbitrary physical memory in a fully controlled way." Sounds a little more advanced than "largely random" to me, and based on the article it sounds like FFS is a step up from "vanilla" Rowhammer...am I missing something?

They can pick a bit or two per page to attack, but then they're stuck with those bits.

In theory they could attack a new bit every few minutes, but that requires a system that allows the victim page to be remapped multiple times. KSM does not; any other memory-merging system could work the same way to mitigate things.

Even if they could keep remapping, it's a very slow attack that way. Reloading the checksum every ten minutes would keep you safe.

Re: New cloud attack takes full control of virtual machines with little effort

#98

Post by saltyhiker »

rotrux wrote: post #83

For those of you worried about your aws workloads, this may help make ya feel a (slight) bit better. https://forums.aws.amazon.com/thread.jspa?messageID=739485&t...

Why only slightly better? The response to that forum post, as far as I can tell, means EC2 is not vulnerable to this attack.

Re: New cloud attack takes full control of virtual machines with little effort

#99

Post by wmf »

willvarfar wrote: post #61
makomk wrote: post #57

Earlier quoted context omitted.

Don't think I've seen any non-server-grade processors in even the cheapest bargain-basement VPS hosts. (Low-end dedicated is different.) Cramming as many VMs into a big server as possible seems to be too important to their cost structure for that.

We perhaps only disagree on what is "server-grade" vs what is sold for servers. Google, for example, are famous for making big data centres out of cheap commodity boxes, and I double Amazon are any different. I certainly know the rackspace blades I've played with didn't make my grade of either! :)

Everything I've read implies that cheap commodity servers like Open Compute are just as reliable as name brand Intel servers (not surprising considering that they're made from the same parts), and ~95% of the market appears to be satisfied with that level of reliability.

Re: New cloud attack takes full control of virtual machines with little effort

#100

Post by Dylan16807 »

ultramancool wrote: post #82
acobster wrote: post #79

Earlier quoted context omitted.

That's where I'm getting a little hazy. The paper says the attacker can "induce bit flips over arbitrary physical memory in a fully controlled way." Sounds a little more advanced than "largely random" to me, and based on the article it sounds like FFS is a step up from "vanilla" Rowhammer...am I missing something?

Yeah, I mean if it won't beat a CRC wouldn't ECC RAM be a reasonably easy solution to this and wouldn't most servers already be secured against it?

ECC RAM makes it a harder, but three bit flips will still survive. It depends on whether the system actually acts properly when it sees a huge amount of ECC errors happening.
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