The Offset Problem Nobody Talks About

You have a kernel read/write primitive on iOS. Congratulations — and also: now what? The jailbreak research community spends enormous energy on obtaining primitives, and almost none documenting what happens in the ten minutes after. A post published April 5, 2026 at reversesociety.co changes that, walking through a repeatable methodology for extracting struct offsets from stripped XNU kernelcaches — validated against iOS 16.7.12 on an iPhone X (build 20H364) using Binary Ninja, with no Kernel Development Kit in sight.

The trigger was a kernel R/W primitive shared by Opa334, described as structurally similar to one used in DarkSword malware. That detail is worth pausing on: the same technique that a researcher uses to map proc offsets on a test device is the same one a malware author used in a documented threat campaign. The methodology is neutral. The intent is not.

←TODAY: iOS 16.7.12 kernelcaches ship stripped — no symbols, raw ARM64, full KASLR in effect.
→3012: As embedded firmware hardens and BACnet controllers adopt ARM cores, offset-extraction discipline moves from jailbreak research into smart-building security audit workflows.
Fulcrum: The same cross-referencing method that maps a proc struct today will map a building-automation controller’s memory layout tomorrow.

The System Architecture Behind the Technique

XNU is Apple’s open-source hybrid kernel — but the iOS production build diverges from the published source. Kernelcaches extracted from IPSW firmware packages arrive without symbols. That sounds like a dead end. It is not, for one structural reason: exported accessor function names are retained even in stripped binaries.

This is the load-bearing insight. Functions like proc_pid(), vnode_mount(), and kauth_cred_getuid() are thin wrappers — one load instruction, one return. Decompiled in Binary Ninja (or IDA Pro with Hex-Rays, or Ghidra), they directly reveal the field offset:

// _proc_pid at 0x5c892c
return *(arg1 + 0x60);

That single ldr w0, [x0, #0x60] tells you: struct proc has p_pid at offset +0x60, and the w register (not x) confirms it is 32-bit. Repeat across kauth_cred_getuid, kauth_cred_getruid, vnode_vtype, and you have a working offset table — built entirely from the binary, no debugger attached.

The workflow runs in three phases. First, locate the kernel base by reading backward until you find the Mach-O magic (0x100000cfeedfacf), then compute the KASLR slide. Second, find anchor globals — allproc, kernproc, nprocs — via adrp/ldr instruction pairs in the __DATA segment; these are entry points into kernel data structures from a known address. Third, work the accessor functions systematically, using the XNU open-source release as a map (field names, struct headers) but never as ground truth — Apple adds, removes, and reorders fields between versions. The proc_ro split, introduced in iOS 15.2+, does not appear in older XNU source releases at all.

The ipsw extraction tool handles kernelcache decryption; blacktop/symbolicator can recover a partial symbol table to reduce manual search. The author deliberately skipped the Kernel Development Kit to force direct ARM64 assembly work — a discipline choice that produces more portable results.

What This Means at the Desk This Week

PAZ readers deploying iPhones and iPads on-site — for Autodesk BIM 360 model review, AR measurements, or site documentation — are running on the same kernel attack surface this methodology exposes. A compromised kernel R/W primitive on a field device is not a theoretical risk: it is the precondition for credential theft, process injection, or silent data exfiltration from project storage. The EU Cyber Resilience Act (CRA), in force from late 2027, will require vendors of connected products — including mobile BIM viewers distributed in Europe — to document vulnerability handling and patch timelines. Knowing what a post-primitive offset-extraction attack looks like is part of the threat model your MDM policy needs to account for.

The methodology transferability is the sharper point for technically oriented readers. Binary analysis tools — Binary Ninja, Ghidra — are not iOS-specific. The same accessor-function-driven offset recovery that maps a ucred struct applies to ARM-based BACnet controllers, IoT sensors, and building-automation firmware. Siguza’s prior work on iOS kernel internals (publicly documented since 2016) and Google Project Zero’s iOS research establish that this class of technique is well-understood by both defenders and attackers. The gap is documentation accessible to engineers who are not full-time security researchers.

Atelier: If your office manages an iPad fleet for site BIM, run a firmware audit baseline now: confirm devices are on iOS 16.7.12 or current, document your MDM enrollment status, and flag any sideloaded apps to your IT security contact. One stripped kernelcache is enough to map your project network if an attacker gets as far as a kernel primitive — the methodology above shows exactly how fast that escalation moves.

Pull the reversesociety.co post, open Binary Ninja’s free tier against a decrypted kernelcache (use ipsw to extract), and trace one accessor — _proc_pid is the clearest starting point. Even if kernel security is not your domain, the binary-reading discipline transfers directly to firmware analysis of embedded building systems. Do it once on a known-good target and you will understand the attack surface of your smart-building infrastructure in a way no vendor datasheet will give you.

Source: Hacker News