AMD 微码签名验证漏洞
文章讨论了AMD处理器微码签名验证漏洞及其潜在风险。攻击者若控制hypervisor和微码，可能导致VM无法信任验证结果。签名密钥依赖于微码版本，若被提取或解密，可能引发安全问题。 2025-2-7 04:35:0 Author: seclists.org(查看原文) 阅读量:10 收藏
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From: Jacob Bachmeyer <jcb62281 () gmail com>
Date: Thu, 6 Feb 2025 22:28:44 -0600
On 2/6/25 17:04, trinity pointard wrote:

If an attacker is able to control the hypervisor (necessary to load
rogue microcode) and the processor microcode, how can the VM trust that
it is actually verifying that attestation and not being sent down a "oh
yes it is exactly what you want it to be" garden path?

Attestations are cryptographically signed by the cpu, and meant to be sent
elsewhere and verified remotely.
That resolves the issue for the VM owner, but still does not address the more interesting question:  is there a way on current AMD processors to perform calculations that cannot be upset by tampered microcode?  (There *was* a subset of instructions on the AMD K8 like that.) 


The key used to sign (VCEK) are dependent on
the microcode version, so it shouldn't be possible to forge new-looking
signature with old microcodes (i would hope this hold would someone be able to
decrypt a microcode, though i couldn't find information on that subject).
If you are correct that the /actual signing key/ used depends on the microcode version, then (logically) the signing key *must* be somewhere in the microcode.  If someone finds a way to decrypt the microcode, for which all keys required must be *somewhere* in every processor that uses that microcode, they would clearly be able to extract the attestation signing key.
I would hope that you are mistaken in that statement that the signing key depends on the microcode version or that we are both missing something somewhere. 


-- Jacob

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文章来源: https://seclists.org/oss-sec/2025/q1/115
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