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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 it should be possible, since apparently previous generations of RAM don't have this problem at all. In the early 90s Intel recalled and replaced, free of charge, CPUs which didn't divide correctly. Perhaps the memory manufacturers today should do the same for rowhammer-affected modules and chips.
Memory errors are particularly disturbing because they are often highly dependent on data and access patterns, and can be extremely difficult to pinpoint without special testing tools. I've personally experienced a situation where a system which otherwise appears to work perfectly well would always corrupt one specific bit of a file when extracting one particular archive.
As a testing tool, MemTest86+ has always worked well for me, and the newer versions can detect rowhammer, although there is this interesting discussion about whether it is actually a problem (to which I say a resounding YES!!!) or if there's some sort of cover-up by the memory industry:
http://www.passmark.com/forum/memtest86/5903-rowhammer-probl...
http://www.passmark.com/forum/memtest86/5475-memtest86-v6-2-...
Run it on your hardware and if it fails, I think you should definitely complain and get it fixed.
> The rowhammer "attack" is successful only because the hardware is just plain broken
I too am of this opinion and am surprised this view isn't widely shared. With DDR4, we should be asking for a refund and/or starting a class-action suit, yet we're putting up with software 'mitigations' instead.
This isn't like the 2008 Phenom TLB bug [1] where the CPU was locking up so AMD released a workaround that kept it from freezing at the expense of a 14% performance penalty. This is like the floating point division bug [2] where the device no longer meets basic operational and accuracy guarantees. RAM cells bleeding into each other ought to be considered a fatal flaw, not some intellectual curiosity.
[1] http://techreport.com/review/13741/phenom-tlb-patch-benchmar...
I too am of this opinion and am surprised this view isn't widely shared. With DDR4, we should be asking for a refund and/or starting a class-action suit, yet we're putting up with software 'mitigations' instead.
I extensively test all the hardware I buy (CPU: LINPACK, RAM: MemTest86+) and if it fails any of those tests, it gets returned as "not fit for purpose". I've done this successfully a few times. A lot of other enthusiasists/power users do the same too, especially if they're overclocking, and searches on other forums show plenty of users testing and finding (mostly other, not rowhammer) errors in newly-bought RAM even when not overclocking. But as noted in the threads I linked to, manufacturers may be trying to cover this up and downplay its severity. Even in the original paper on rowhammer, the authors didn't disclose which manufacturers and which modules were affected, although I think this should really be treated like the FDIV bug: name and shame. I blame political correctness...
FDIV was really not technically a serious errata in the grand scheme of erratas. The Phenom TLB bug was worse. Intel basically denied/sat on the issue for half a year, stopped just short of slandering Dr. Nicely, etc, they made it into a complete PR disaster. If they came out the week after it was reported and just said, here's a workaround, here's an opt-in replacement program (which they finally did, but then it was too late), you would probably never have heard about the FDIV bug -- like the countless other errata we have software workarounds for.
Back in the day, when I were a hardware engineer, we called this "pattern sensitivity" and it was a defect!
I don't agree, there is software that is designed to run on faulty hardware. This is often in high radiation environments (see: outer space). I agree this is not an area that much hardening has been done in conventional security models, but in other environments, it is common to use CRC error detection, parity information or other means to ensure that even if data is partially corrupted, that the original can be restored.
I see no reason to prevent someone from implementing this sort of error correction for GPG and other important cryptography.
Hostile environments attack your software without intelligence. (When working with them, it may seem otherwise, but that's just cynicism.) Hostile people attack intelligently. Whatever mitigation you may imagine is possible by checking CRCs or something after the fact, you must account for the possibility that the software, the OS, or the CRC has also been attacked by a hostile intelligent adversary. The fact that we can make reliable software in the face of unintelligent attacks is not evidence that we can make secure software in the face of intelligent ones.
Rowhammer is too powerful a technique to expect secure software to run on machines affected by it. This is an attack based on using rowhammer to change bits in other VM's memory. The only sane response to that, from the perspective of writing secure software, is despair. You can't deal with attackers in possession of that primitive.
This does not make sense. If an attacker an alter your data, he can alter your CRC codes as well. Or just replace the pointer to the checkCRC function to "return true".
without being an expert in this area; my gut feel is that the fix to this problem is likely going to be funded by the end user. Given that competition continues to drive prices down, would 'secure ram' be viable? would you pay more for it?
Given that competition continues to drive prices down, would 'secure ram' be viable? would you pay more for it?
It's funny you mention this, since the problem only affects newer DDR3 and DDR4 modules and older RAM (EDO modules are apparently still in limited production and being sold) does tend to be significantly more expensive. Unfortunately the rest of the hardware needs to be compatible.
This also means all the older hardware that gets scrapped in massive quantities daily is likely to contain RAM immune to this problem, which is somewhat ironic... maybe it's just a (sad) continuation of the "newer is more volatile" trend that can be traced back to thousand-year-old stone tablets which remain readable today.
I have the same opinion as you. I would but most people wouldn't. The root cause of the problem is since the trend about ram is "the bigger the better" (in terms of GBs) we have tons of capacitors on a small surface. I'm no expert too but I think there's no simple hardware fix for this instead of returning back to RAMs that hold less memory, but most people won't accept it. Maybe we're hitting the limits of the current technology and we should switch to another one. Just on a side note two years ago one of my professors quoted an ongoing research in my university about RAM that instead of storing electrons formed crystals, but I don't know any other detail about this.
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.
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.
It seems the HN title and original title are both pretty wrong, at least according to the article content. The attack vector is really the ability to, if you have a known public key and a server using it, perform a pre-calculated bit flip such that the new public key is much easier to factor, and thus obtain a corresponding private key.
So you're not obtaining original private keys, you're altering original public keys so that you can more quickly factor a private key that will be accepted.
If this is an SSH public key, then you can obtain SSH access. If it's a PGP key trusted by the package manager, then you can craft signatures on packages that would be accepted as valid, assuming you can also get the target machine to download said package.
I think SSH is probably the most interesting attack vector assuming you can get network access to the host once you've jumped through the myriad hoops to perform this attack.
It's a serious issue that should be addressed (probably via forced from-disk reads or at minimum integrity checks), but I think the authors are perhaps a little too eager on the practical implications of corrupting in-memory public keys.
It's the sort of thing for which the NSA would spend their resources to develop an exploit tool.
In the paper, they compromise not only the pgp key but also the Debian update server address, so all that is necessary is a software update to be compromised.
Another attack would be to flip bits in code pages...
That the attackers illustrated it by changing public keys so they could push updates or ssh into a box doesn't mean that's all the ways they could have compromised. You can't say "I don't use SSH so I'm safe!" or anything like that.
Here's the crux of the memory issue from one of the link in the article:
DDR memory is laid out in an array of rows and columns, which are assigned in large blocks to various applications and operating system resources. To protect the integrity and security of the entire system, each large chunk of memory is contained in a "sandbox" that can be accessed only by a given app or OS process. Bit flipping works when a hacker-developed app or process accesses two carefully selected rows of memory hundreds of thousands of times in a tiny fraction of a second. By hammering the two "aggressor" memory regions, the exploit can reverse one or more bits in a third "victim" location. In other words, selected zeros in the victim region will turn into ones or vice versa.
Rowhammer itself has been around a while, and is only 50% of this attack that has been posted.
The other bit is the newer idea (well, old idea, newer actual implementation); memory deduplication by your hypervisor leads to a very minor timing fingerprint when you write to a page of memory that had previously been deduplicated IE the same physical page was shared amongst multiple VM's because it was identical.. until you wrote to it and the OS/hardware had to then Copy-on-Write it out to your own dedicated copy; that has a higher latency than a memory page that is already available directly for writing to you.
So it doesn't allow reading any data? I'm most nervous about leaking private keys.
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...
Sharing pages seems a big price risk to pay for saving a little memory.
Why not turn it off entirely?
People are focusing too much on the exact specific attack shown here: Deduplication, modifying a public key, etc. (And proposing solutions like turning off deduplicaiton, checksum, etc.)
But that's just this attack - the fact that they have that much control over memory means there are FAR FAR FAR more possible attacks.
If you can control memory to that level then you are limited only by your imagination.
The only mitigation I can think of at the moment is ECC memory. And shame on Intel for only supporting that on Xeon.
What can you do to attack other VMs if you don't have shared memory with them?
If you control memory vs. if you control your memory. This does not give you general purpose access.
That used to be a point in AMD's favor for their desktop CPUs.
It is more costly, but this is a good reason to use a dedicated chunk of memory for every Xen PV domU. No oversubscription!
Allowing multiple domU VMs on the same dom0 (or the equivalent in other hypervisor platforms) to re-use memory and balloon/contract memory on the fly is what enables this.
Can you point me to some services that provide, specifically, Xen PV VMs with non-oversubscribed memory?
I'm considering deploying a custom unikernel for protecting the private key data for my app[1], until I have enough money for a Hardware Security Module.
[1] http://security.stackexchange.com/questions/135457/penetrati...
I suppose this would still be susceptible to this class of attack: https://www.usenix.org/conference/usenixsecurity16/technical...
Unless you're very careful about which ranges of physical memory are mapped to each VM.
"For the attacks to work, the cloud hosting the VM must have deduplication enabled so that physical pages are shared between customers."
But the vendor's cloud will not disable sharing pages of physical memory because ____.
This is a great counterpoint to the salesman trying to sell you on "cloud" anything.
Why is it less expensive to use the "cloud"?
One reason is because you do not get your own physical server, including your own RAM.
When the "cloud" buzz began to gain momentum years ago I raised the issue of not knowing who your "neighbors" were on these physical servers that customers are sharing with other customers in datacenters.
As usual, these concerns will just fade into the background... again.
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.
Will rowhammer attacks work against ECC RAM? Multibit memory errors should be detected, even if they can't be corrected.
ECC is one of the mitigations, as well as increased refresh rate.
The 'best' solution is better ram: some vendors are more vulnerable than others.
Would this be a threat to services running on AWS?
No, because AFAIK EC2 does not dedupe RAM.
Ouch. Before reading this article I was seriously considering deploying a signing service as a HaLVM (Haskell) Xen PV unikernel running on EC2. The service would receive its private key after startup, such that the key never touches disk. Now I'm a lot less inclined to pretend that the Xen interface actually protects me...
Xen has had page-table and interrupt vector related security vulnerabilities. But I don't think EC2 would use non-ECC RAM, so I don't think it's vulnerable to this "rowhammer" technique. (I also don't think EC2 would do cross-VM page deduplication, another necessary condition.)
Afaik xen does not use memory deduplication. KVM aside, one should be worried about things running inside a linux host/vm, like containers. Maybe I am missing something
For the attacks to work, the cloud hosting the VM must have deduplication enabled so that physical pages are shared between customers.
This "Flip Feng Shui" wouldn't work in SmartOS simply because the hypervisor does not implement memory deduplication.
Good luck with VMware though.
It seems like a dedicated server would solve this issue in some sense. If your not on a shared VM, then an attacker could not affect the memory.
For those that cannot be on a dedicated server, what changes could be made to the shared VM memory setup to reduce this attack surface?
some thoughts:
For the attacks to work, the cloud hosting the VMs must have deduplication enabled so that physical pages are shared between customers.
its not (afaik) heartbleed time. It's bad but the effort required is high and afaik the attacker will replace your key with their key - making it clear you are compromised.
The abstract says the attack allows "flips over arbitrary physical memory in a fully controlled way." If I'm understanding that correctly, it would be trivial to then restore the old key alongside it, leaving the victim none the wiser.
Also, as others have pointed out, this is a hardware issue and the clear solution is to swap out the vulnerable RAM. Yeah, paying more is an "easy" way to have peace of mind (if that's even an option for you as a "cloud hoster"), but that's just backwards IMHO: a security vulnerability on the host's side should not translate into an upsell.
I wonder if it would be worth checksumming public keys and re-checking the checksum each time it's used?
If your threat model now includes 'the attacker can at arbitrary times make arbitrary alterations to the working memory of my process' then no, this won't help. You can't trust the checksum, you can't trust that the data you just check summed hasn't subsequently changed, and you can't trust that data which passes a checksum wasn't previously different. Also you can't trust the checksum code itself. Or the operating system you're running on. Or anything.
That's security by obscurity (which may work to delay the attacker). If an attacker can modify your public keys he can modify your checksums as well.
Seems to me that a public key should be identified by a cryptographic hash of it, rather than the public keys itself. Then the attacker would need to replace the entire hash, rather than just a few bits, because the hash changes completely just by flipping a single bit in the input.
Something like Perspectives for Firefox?
Is Linode safe?