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Comment by ionforce | Hacker News Reader

Is this saying that AMD is affected? Is this the same as the Intel bug reported earlier?

Yes, AMD is affected. There are multiple vulnerabilities (Project Zero refers to 3 separate "variants", variant 1 and 2 being called "Spectre" and variant 3 being called "Meltdown"). The most serious variant only affects Intel, but can be patched. The other 2 variants affect AMD, ARM, and Intel, and cannot be patched.

See this excerpt from spectreattack.com:

>Which systems are affected by Meltdown?

>Desktop, Laptop, and Cloud computers may be affected by Meltdown. More technically, every Intel processor which implements out-of-order execution is potentially affected, which is effectively every processor since 1995 (except Intel Itanium and Intel Atom before 2013). We successfully tested Meltdown on Intel processor generations released as early as 2011. Currently, we have only verified Meltdown on Intel processors. At the moment, it is unclear whether ARM and AMD processors are also affected by Meltdown.

>Which systems are affected by Spectre?

>Almost every system is affected by Spectre: Desktops, Laptops, Cloud Servers, as well as Smartphones. More specifically, all modern processors capable of keeping many instructions in flight are potentially vulnerable. In particular, we have verified Spectre on Intel, AMD, and ARM processors.

Of the variants of the attack that can leak privileged memory, AMD is only impacted if a non-default kernel configuration is enabled: "BPF JIT"

This is not correct. That's just what the POC chose to implement.

Google security blog says it is.

> These vulnerabilities affect many CPUs, including those from AMD, ARM, and Intel, as well as the devices and operating systems running them.

https://security.googleblog.com/2018/01/todays-cpu-vulnerabi...

That's unclear, to the point of being factually wrong. Variant 2 and Variant 3 POCs only affect Intel, and those are the ones people are most talking about, and at least to me, the most concerning.

Treating them as a group, ignores the very real differences in effect.

https://googleprojectzero.blogspot.com/2018/01/reading-privi...

https://meltdownattack.com/meltdown.pdf

>6.4 Limitations on ARM and AMD We also tried to reproduce the Meltdown bug on several ARM and AMD CPUs. However, we did not manage to successfully leak kernel memory with the attack described in Section 5, neither on ARM nor on AMD. The reasons for this can be manifold. First of all, our implementation might simply be too slow and a more optimized version might succeed. For instance, a more shallow out-of-order execution pipeline could tip the race condition towards against the data leakage. Similarly, if the processor lacks certain features, e.g., no re-order buffer, our current implementation might not be able to leak data. However, for both ARM and AMD, the toy example as described in Section 3 works reliably, indicating that out-of-order execution generally occurs and instructions past illegal memory accesses are also performed.

Seems like the possibility exists that AMD/ARM could be affected, based on the behavior they saw, but they were not able to successfully verify.

That's fair, but the leads on multiple press releases are that this affects all processors equally which feels very disingenuous to me. Intel's latest press release for example.

the intel behaviour is probably the result of an optimization / architectural decision. like when the micro ops fetch a value from memory they are probably fetching the real value then setting a flag that the instruction is invalid. like it might be cheaper to deal with the problem later in the pipeline than earlier.

but it might also be reasonable in a different architecture to fetch 0 straight away to the micro op when the memory access is invalid and set a flag to raise the exception as well. in this situation you don't have the problem because you are just shuffling around invalid data.

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