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> Specifically, a malicious hypervisor can selectively drop any writes of an AMD SEV-ES and SEV-SNP guest that occurred at an attacker-chosen point This strike

> Specifically, a malicious hypervisor can selectively drop any writes of an AMD SEV-ES and SEV-SNP guest that occurred at an attacker-chosen point This strikes me as the thing that Raymond Chen calls "being on the other side of this airtight hatchway" [0]. That is, if you've already got control of the Hypervisor then ... you can do anything you want to the guest operating systems. Right? 0: https://devblogs.microsoft.com/oldnewthing/20060508-22/?p=31283 https://devblogs.microsoft.com/oldnewthing/20060508-22/?p=31...

depereo 3y ago
SEV is supposed to protect against exactly that scenario, so it's fairly serious that this protection is unwound here.
kiririn 3y ago
Protection against a rogue hypervisor is the main benefit of SEV. The whole point is to raise VM security to equivalent of a bare metal machine with encrypted memory and no exposed DMA channels. Protection from other guests is a nice side effect but should be a given Sadly this means AWS are still the only ones offering this kind of confidential computing without known flaws, and probably only because they don’t have researchers attempting attacks like this on their graviton CPUs
- deleted 3y ago
  [deleted]
- colmmacc 3y ago
  I work at AWS on these systems. We do fund research on Graviton. But our main approach to "Confidential Computing" has always been very different and based on the Nitro system. We run our virtualization on dedicated Nitro cards, with their own CPUs and memory, that are separate from the hardware running customer's EC2 instances. The Nitro system is hermetic and doesn't grant us access to a customer's memory or operations, and the simple design and interface is there to minimize the surface area for any potential issues. (We also put all this in our terms of service). All customers on Nitro get that enhanced confidentiality between their instance and us as a cloud provider, but for customers who want to run workloads that are confidential from themselves, we do also offer AMD SEV based instances as well as our own Nitro Enclaves product.
  - jbott 3y ago
    For those of us that don’t work at AWS, their docs are actually quite good at describing the Nitro system, very interesting read: https://docs.aws.amazon.com/whitepapers/latest/security-design-of-aws-nitro-system/security-design-of-aws-nitro-system.html https://docs.aws.amazon.com/whitepapers/latest/security-desi...
  - jakobson14 3y ago
    Essentially, you're giving each customer not a VM but a physical blade server?
- jakobson14 3y ago
  Frankly, this whole exercise of "don't trust the cloud host" is pretty dumb. Flaws in chipset vendor products and new avenues of fuckery will continue to to be found. Expecting that you can trust a computer you've never even seen, let alone one you *know* is a VM with a whole other untrusted OS under it, is a fool's errand. If you need this level of trust, you should be on-prem. No excuses.

depereo 3y ago

SEV is supposed to protect against exactly that scenario, so it's fairly serious that this protection is unwound here.

kiririn 3y ago

Protection against a rogue hypervisor is the main benefit of SEV. The whole point is to raise VM security to equivalent of a bare metal machine with encrypted memory and no exposed DMA channels. Protection from other guests is a nice side effect but should be a given Sadly this means AWS are still the only ones offering this kind of confidential computing without known flaws, and probably only because they don’t have researchers attempting attacks like this on their graviton CPUs

deleted 3y ago
[deleted]
colmmacc 3y ago
I work at AWS on these systems. We do fund research on Graviton. But our main approach to "Confidential Computing" has always been very different and based on the Nitro system. We run our virtualization on dedicated Nitro cards, with their own CPUs and memory, that are separate from the hardware running customer's EC2 instances. The Nitro system is hermetic and doesn't grant us access to a customer's memory or operations, and the simple design and interface is there to minimize the surface area for any potential issues. (We also put all this in our terms of service). All customers on Nitro get that enhanced confidentiality between their instance and us as a cloud provider, but for customers who want to run workloads that are confidential from themselves, we do also offer AMD SEV based instances as well as our own Nitro Enclaves product.
- jbott 3y ago
  For those of us that don’t work at AWS, their docs are actually quite good at describing the Nitro system, very interesting read: https://docs.aws.amazon.com/whitepapers/latest/security-design-of-aws-nitro-system/security-design-of-aws-nitro-system.html https://docs.aws.amazon.com/whitepapers/latest/security-desi...
- jakobson14 3y ago
  Essentially, you're giving each customer not a VM but a physical blade server?
jakobson14 3y ago
Frankly, this whole exercise of "don't trust the cloud host" is pretty dumb. Flaws in chipset vendor products and new avenues of fuckery will continue to to be found. Expecting that you can trust a computer you've never even seen, let alone one you *know* is a VM with a whole other untrusted OS under it, is a fool's errand. If you need this level of trust, you should be on-prem. No excuses.