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Sven Peter
Personal blog · blog.svenpeter.dev/posts · on HN as svenpeterhardwaresystemssecurity
Sven Peter's personal blog at blog.svenpeter.dev covers hardware, systems and security. Since 2021, 8 different Hacker News readers have linked it 8 times, most often “Apple Silicon Hardware: SPRR and Guarded Exception Levels (GXF)”. The last post was in 2021, but the archive is still widely read.
Too few sampled comments (3) to say how often HN recommends it.?
Why HN links it
HN readers link this blog for technical posts on Apple silicon and macOS internals, such as the M1's GXF and SPRR mechanisms, kernel extensions and iOS JIT. Comments cite it as a reference for those details.
Summarised by Claude from a sample of 3 HN comments that link here. Each comment is marked recommending, critical or neutral (citing without judging); how this works.
Most-linked posts?
- Apple Silicon Hardware: SPRR and Guarded Exception Levels (GXF)7 people · 7 mentions · first linked 2021-05-06
What Hacker News says?
Yes, you are right that they allow their own JIT. Their position would be that they spend a great deal of time hardening that JIT and don't trust others to take that time. Their JIT isn't perfect of course, but they control it and can fix it fast if needed. (In their opinion.) They are really saying that they aren't willing to take the time to exhaustively test other JITs. That is a frustrating choice, but I do unde…
Comment linking /posts/m1_sprr_gxf/
on “We’ll stop selling our Code Editor app for iOS soon”Submitted Apple Silicon Hardware: SPRR and Guarded Exception Levels (GXF) as a story · 272 points
HN discussionUsually, once you can run code in kernel mode it’s just a matter of bringing the hardware back to a sane state. Unfortunately, “just” running code in kernel mode is incredibly hard on the iPad. There’s e.g. a hardware mitigation that turns a memory region to read-only and also only allows kernel code to run from this region. This mitigation is locked down and cannot be disabled once XNU is running on the iPad ( http…
Comment linking /posts/m1_sprr_gxf
on “Debian GNU/Linux running bare metal on the Apple M1 with a mainline kernel”Submitted Apple Silicon Hardware Secrets: SPRR and Guarded Exception Levels (GXF) as a story · 23 points
HN discussionThe funny thing is that the M1 has an undocumented but totally used feature called Guarded Execution[0] that lets you separate parts of the kernel (or hypervisor, if you're in EL2) from one another. Basically, on the M1 each Exception Level now has a regular and a guarded sublevel, with their own page table permissions, and special instructions to enter or exit the guarded execution within the same EL. macOS on the…
Comment linking /posts/m1_sprr_gxf/
on “macOS extensions are moving away from the kernel”Submitted Apple Silicon Hardware Secrets: SPRR and Guarded Exception Levels (GXF) as a story · 20 points
HN discussionConsidering Apple have custom extensions to ARM already, they'd be giving up more than just the SoC design if they switched to a standard ARM core, unless eventually all those extensions get upstreamed into the spec... but I don't see GXF [1] getting upstreamed, at least not like that. That one is just crazy. [1] https://blog.svenpeter.dev/posts/m1_sprr_gxf/
Comment linking /posts/m1_sprr_gxf/
on “Key M1 Mac Engineer Departs Apple for Intel”Submitted Apple Silicon Hardware Secrets: SPRR and Guarded Exception Levels (GXF) (2021) as a story · 2 points
HN discussion