3 ms·
> On Darwin, x18 is used [...] on hardware where Meltdown mitigations are needed. [...] On M1, it's currently usable by applications I’m confused. x18 is an AR
by NobodyNada 5y ago
> On Darwin, x18 is used [...] on hardware where Meltdown mitigations are needed. [...] On M1, it's currently usable by applications
I’m confused. x18 is an ARM register, but I thought Meltdown only affected x86 chips. Were iOS devices vulnerable to Meltdown too? Or did you mean not x18 specifically but some equivalent OS-reserved x86 register?
- somebody_amzn 5y agoYeah, Meltdown did affect quite some Arm CPUs, including the Cortex-A75 too. However, due to specific features of the Arm architecture, it was patchable without a significant performance hit. (see this section: https://siguza.github.io/KTRR/#meltdownspectre-mitigations-112 https://siguza.github.io/KTRR/#meltdownspectre-mitigations-1..., which made the need for actually doing a page table switch avoidable)
- NobodyNada 5y agoInteresting, thanks for the link!