[PATCH gnupg v12] Disable CPU speculation-related misfeatures

[Andrew Gallagher]

On 11 Jul 2025, at 04:02, Jacob Bachmeyer via Gnupg-devel <gnupg-devel at gnupg.org> wrote:
> 
> Generally, GnuPG does not consider local side channels to be in-scope for its security model, as there are countless ways for Mallory to make off with your key if he can get that close in the first place. Note that Mallory, in the cryptographic sense, may be an otherwise trusted party, such as the administration of a cloud VM hosting service.

But many side channels, such as those arising from speculative execution, are observable by an unpriviliged third party user of a VM host (and not just cloud, on-prem is no different in principle). Such a user would not normally be expected to have direct access to your key material, so the existence of side channels is a significant change in the threat model. Note also that in principle a speculative execution side channel can be observed from arbitrary javascript or wasm code running in a web browser, which is not what people normally think of when you say “only if Mallory has access to your machine”.

It worries me that some of the advice given on this list over the last few days appears to say that gnupg should not be installed on VMs because speculative execution side channels are not going to be fixed. If speculative execution side channels are out of scope, then does it not logically follow that gnupg should not be installed on a computer with a web browser?

A