#+title: Curiosities, Directions and Supplemental Information
#+date: 2026-05-18 Mon
#+author: W. Kosior
#+email: wkosior@agh.edu.pl

* Android Security
- SELinux
- account per application
- APIs for cross-app communication

* App Side-Loading (Google Android)
- historically allowed
- developer verification
  - 2025 — announcement
  - September 2026 — Brazil, Singapore, Indonesia, and Thailand
  - 2027 — global
- required application approval by Google
  - developer identification & terms acceptance
  - hobbyist with email — up to 20 installs
- https://github.com/woheller69/FreeDroidWarn
- custom ROMs

* Play Integrity API
- API to check the application it is not debugged / modified
- BASIC, DEVICE, STRONG
- hardware attestation
- Magisk, PIF

* App Side-Loading (Apple iOS)
- historically disallowed
- DMA
- March 2024 — alt stores
  - still no real sideloading
  - stores controlled by Apple

* DMA AI Access
- Gemini system access on Android
- other models
- https://dataconomy.com/2026/05/14/apple-google-eu-criticize-ai-access/

* Router Freedom
- use one's chosen router & modem
- copper wire & opic fibre
  - "ISPs hate him"

* Radio Freedom
- lock radio devices?
  - WiFi, GPS, etc.
- 2014
- proposed legal requirement on manufacturers
- January 2026 — plans abandoned
  - FSFE advocacy

* LLM CVEs
- spring 2026
- hundreds of (Linux kernel) security bug reports
  - low quality → high quality reports
- Copy Fail (CVE-2026-31431)
  - April 29, 2026
    - few weeks after report to kernel
  - local privilege esalation
    - worst in years
  - distributrions not notified
    - not the job of kernel devs
    - usually done by researchers themselves (not here)
  - CVSS score only 7.8
    - lost in hundreds others

* Kernel Livepatch
- rebootless security fixes
- earlier: ksplice (Oracle), kGraft (SuSE), kpatch (Red Hat)
- load a specifically-prepared kernel module
- hijack a function using ftrace

* Rust in OS development
- Linux kernel "Rust experiment"
  - "stable" since April 12, 2026 (Linux 7.0)
  - old driver rewrites
  - Apple GPU driver
    - disagreements
    - not mainlined
- userspace
  - uutils
- from ground up
  - e.g., Redox OS (2015)
  - "has real potential, but it is not there yet, but is worth watching..."
    ~ /Andrew S. Tanenbaum (2025)/

* ASLR
- what is the =malloc()= address in this process' virtual address space?
- PIC, PIE
- ASLR bypasses

* Meltdown & Spectre
- 2017/2018
  - speculated years earlier
- timing attacks
- x86 and not only
- read kernel address space
- read process' address space
- JIT sandboxes (e.g., JavaScript)
- mitigations (retpoline, clock granularity, separate process or VM)

* Microkernel vs Monolithic Kernel
- kernel- or user-space drivers?
- Tannenbaum-Torvalds debate (90s)
- microkernel
  - driver flaws not fatal
  - easier driver debugging
  - e.g., Mach, kernel of MINIX, L4, Zircon (Fuschia's kernel)
- monolithic kernel
  - less context switches (efficiency)
  - simpler design (time to market)
  - e.g., Linux, most UNIX'es

* Fuschia
- 2016 — first Google code release
- 2021 — actual product (Google smart speakers)
- non-UNIX, instead:
  - namespaces
  - capabilities
    - *not* like Linux/POSIX capabilities
    - similarities with AppArmor rules or Windows tokens
    - more: https://arxiv.org/pdf/2108.04183

* MINIX 3
- Andrew S. Tannenbaum
  - a didactic OS
- restarting of crashed drivers
- powers modern Intel ME

* Hybrid Kernels
- Windows (NT, aka 1993-present)
- XNU (Apple OSes)
- GNU HURD
- «As to the whole "hybrid kernel" thing - it's just marketing"»
  ~ /Linus Torvalds (2006)/

* Rump Kernel
- same driver loadable as userspace or kernelspace
- NetBSD
- note related features like UIO/FUSE (Linux)

* Hardware Considerations
- proprietary blobs
  - microcode (CISC vs RISC)
  - "Ring -3"
    - Intel ME (all post-2009)
    - AMD PSP (all post-2013)
  - others (GPUs, radios, etc.)
    - "new" NVIDIA drivers (May 2022)
    - *firmware*

* Hardware Considerations — ISAs
- x86
  - Intel & AMD duopoly
    - there is also a third company nobody recognizes
  - only major CISC (microcode issue)

* Hardware Considerations — ISAs, Cont.
- x86
- ARM
  - patents & designs licensed from ARM Holdings plc
  - fabless
  - good competition

* Hardware Considerations — ISAs, Cont…
- x86
- ARM
- MIPS
  - out of fashion

* Hardware Considerations — ISAs, Cont…
- x86
- ARM
- MIPS
- SPARC
  - released by Sun Microsytems, locked by Oracle

* Hardware Considerations — ISAs, Cont…
- x86
- ARM
- MIPS
- SPARC
- (Open)POWER
  - Linux Foundation
  - TALOS II
  - servers

* Hardware Considerations — ISAs, Cont…
- x86
- ARM
- MIPS
- SPARC
- (Open)POWER
- RISC-V
  - royalty-free
  - 2010
  - 2018 — RISC-V base ISA and privileged architecture specifications

* DMA attacks
- cellular modems (!)
- back to firmware blobs issue
- IOMMU

* Cold boot attacks
- DDR2, DDR3, DDR3
- Cache-as-RAM?