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Chrome OS Internals Chrome OS Internals Josh Triplett [email protected] LinuxCon Europe 2014 Josh Triplett Chrome OS Internals LinuxCon Europe 2014 1 / 43 Overview Intro to Chrome OS Architecture of Chrome OS Verified boot and developer mode Security Build a bootable Chromium OS image from source Develop Chrome OS Josh Triplett Chrome OS Internals LinuxCon Europe 2014 2 / 43 Chrome OS Operating system from Google based on the Chrome browser Designed around web apps Browser, Gmail, Google Docs, YouTube, Netflix, games Google Drive, Chrome Sync, and persistent app state Synced, backed up, and updated automatically Josh Triplett Chrome OS Internals LinuxCon Europe 2014 3 / 43 Digital signature from Google Runs on systems in production mode Branding Flash, Netflix, and DRM Chromium OS and Chrome OS Built from publically available Open Source code Only runs on devices in developer mode Allows shell and root access No Flash, Netflix, DRM Josh Triplett Chrome OS Internals LinuxCon Europe 2014 4 / 43 Chromium OS and Chrome OS Built from publically available Digital signature from Google Open Source code Runs on systems in production Only runs on devices in mode developer mode Branding Allows shell and root access Flash, Netflix, and DRM No Flash, Netflix, DRM Josh Triplett Chrome OS Internals LinuxCon Europe 2014 4 / 43 Architecture HTML5 Websites Chrome Apps Browser Extensions Blink engine, V8 JavaScript, Native Client Chromium browser Userspace: init, libraries, services, graphics, 3D Linux kernel Customized firmware (coreboot) Chrome OS hardware Josh Triplett Chrome OS Internals LinuxCon Europe 2014 5 / 43 Arbitrary Linux-compatible PC hardware Always effectively in developer mode Chrome OS Hardware Chromebook laptops Chromebox desktops Chromebase \all-in-ones" (built into a monitor) Josh Triplett Chrome OS Internals LinuxCon Europe 2014 6 / 43 Chrome OS Hardware Chromebook laptops Chromebox desktops Chromebase \all-in-ones" (built into a monitor) Arbitrary Linux-compatible PC hardware Always effectively in developer mode Josh Triplett Chrome OS Internals LinuxCon Europe 2014 6 / 43 Haswell: Star Fox fox, slippy, falco, peppy Baytrail: Donkey Kong rambi, squawks, quawks, swanky Hardware codenames Popular video game series for each hardware family Character for each model in that family Josh Triplett Chrome OS Internals LinuxCon Europe 2014 7 / 43 Baytrail: Donkey Kong rambi, squawks, quawks, swanky Hardware codenames Popular video game series for each hardware family Character for each model in that family Haswell: Star Fox fox, slippy, falco, peppy Josh Triplett Chrome OS Internals LinuxCon Europe 2014 7 / 43 Hardware codenames Popular video game series for each hardware family Character for each model in that family Haswell: Star Fox fox, slippy, falco, peppy Baytrail: Donkey Kong rambi, squawks, quawks, swanky Josh Triplett Chrome OS Internals LinuxCon Europe 2014 7 / 43 Key differences in Chrome OS hardware Developer-mode switch (physical or keyboard-based) Custom keyboard and keyboard controller Hardware on Google compatibility list Embedded controller with Open Source firmware Uses coreboot-based Chrome OS firmware Josh Triplett Chrome OS Internals LinuxCon Europe 2014 8 / 43 Coreboot provides the framework for hardware initialization \depthcharge": u-boot as coreboot payload Provides flexible boot of Linux from various media Read-only firmware for root of trust and recovery mode A/B read-write firmware available for fallbacks during updates Includes SeaBIOS to boot arbitrary OSes Open Source firmware for embedded controller Implements verified boot procedure Enforces developer-mode switch requirements Physical presence (switch or keyboard) Wiping local state when switching Chrome OS firmware Based on coreboot and u-boot Josh Triplett Chrome OS Internals LinuxCon Europe 2014 9 / 43 Read-only firmware for root of trust and recovery mode A/B read-write firmware available for fallbacks during updates Includes SeaBIOS to boot arbitrary OSes Open Source firmware for embedded controller Implements verified boot procedure Enforces developer-mode switch requirements Physical presence (switch or keyboard) Wiping local state when switching Chrome OS firmware Based on coreboot and u-boot Coreboot provides the framework for hardware initialization \depthcharge": u-boot as coreboot payload Provides flexible boot of Linux from various media Josh Triplett Chrome OS Internals LinuxCon Europe 2014 9 / 43 Open Source firmware for embedded controller Implements verified boot procedure Enforces developer-mode switch requirements Physical presence (switch or keyboard) Wiping local state when switching Chrome OS firmware Based on coreboot and u-boot Coreboot provides the framework for hardware initialization \depthcharge": u-boot as coreboot payload Provides flexible boot of Linux from various media Read-only firmware for root of trust and recovery mode A/B read-write firmware available for fallbacks during updates Includes SeaBIOS to boot arbitrary OSes Josh Triplett Chrome OS Internals LinuxCon Europe 2014 9 / 43 Implements verified boot procedure Enforces developer-mode switch requirements Physical presence (switch or keyboard) Wiping local state when switching Chrome OS firmware Based on coreboot and u-boot Coreboot provides the framework for hardware initialization \depthcharge": u-boot as coreboot payload Provides flexible boot of Linux from various media Read-only firmware for root of trust and recovery mode A/B read-write firmware available for fallbacks during updates Includes SeaBIOS to boot arbitrary OSes Open Source firmware for embedded controller Josh Triplett Chrome OS Internals LinuxCon Europe 2014 9 / 43 Enforces developer-mode switch requirements Physical presence (switch or keyboard) Wiping local state when switching Chrome OS firmware Based on coreboot and u-boot Coreboot provides the framework for hardware initialization \depthcharge": u-boot as coreboot payload Provides flexible boot of Linux from various media Read-only firmware for root of trust and recovery mode A/B read-write firmware available for fallbacks during updates Includes SeaBIOS to boot arbitrary OSes Open Source firmware for embedded controller Implements verified boot procedure Josh Triplett Chrome OS Internals LinuxCon Europe 2014 9 / 43 Chrome OS firmware Based on coreboot and u-boot Coreboot provides the framework for hardware initialization \depthcharge": u-boot as coreboot payload Provides flexible boot of Linux from various media Read-only firmware for root of trust and recovery mode A/B read-write firmware available for fallbacks during updates Includes SeaBIOS to boot arbitrary OSes Open Source firmware for embedded controller Implements verified boot procedure Enforces developer-mode switch requirements Physical presence (switch or keyboard) Wiping local state when switching Josh Triplett Chrome OS Internals LinuxCon Europe 2014 9 / 43 All third-party code runs in a sandbox. Verified Boot Modules Userspace Browser Root filesystem (A/B) Hash (dm-verity) Kernel and kernel arguments (A/B) Signature Updatable firmware and bootloader (A/B) Signature Root of trust: Read-only firmware Josh Triplett Chrome OS Internals LinuxCon Europe 2014 10 / 43 Verified Boot Modules Userspace Browser Root filesystem (A/B) Hash (dm-verity) Kernel and kernel arguments (A/B) Signature Updatable firmware and bootloader (A/B) Signature Root of trust: Read-only firmware All third-party code runs in a sandbox. Josh Triplett Chrome OS Internals LinuxCon Europe 2014 10 / 43 Tip: Refresh-Power is instant hard reset Allows bypassing verified boot via explicit keyboard interaction Enforced in firmware or embedded controller Not changeable from OS Wipes stateful partition, after enforced delay Allows booting USB or BIOS Developer mode Physical switch on older hardware Esc-Refresh-Power on newer hardware Josh Triplett Chrome OS Internals LinuxCon Europe 2014 11 / 43 Allows bypassing verified boot via explicit keyboard interaction Enforced in firmware or embedded controller Not changeable from OS Wipes stateful partition, after enforced delay Allows booting USB or BIOS Developer mode Physical switch on older hardware Esc-Refresh-Power on newer hardware Tip: Refresh-Power is instant hard reset Josh Triplett Chrome OS Internals LinuxCon Europe 2014 11 / 43 Wipes stateful partition, after enforced delay Allows booting USB or BIOS Developer mode Physical switch on older hardware Esc-Refresh-Power on newer hardware Tip: Refresh-Power is instant hard reset Allows bypassing verified boot via explicit keyboard interaction Enforced in firmware or embedded controller Not changeable from OS Josh Triplett Chrome OS Internals LinuxCon Europe 2014 11 / 43 Allows booting USB or BIOS Developer mode Physical switch on older hardware Esc-Refresh-Power on newer hardware Tip: Refresh-Power is instant hard reset Allows bypassing verified boot via explicit keyboard interaction Enforced in firmware or embedded controller Not changeable from OS Wipes stateful partition, after enforced delay Josh Triplett Chrome OS Internals LinuxCon Europe 2014 11 / 43 Developer mode Physical switch on older hardware Esc-Refresh-Power on newer hardware Tip: Refresh-Power is instant hard reset Allows bypassing verified boot via explicit keyboard interaction Enforced in firmware or embedded controller Not changeable from OS Wipes stateful partition, after enforced delay Allows booting USB or BIOS Josh Triplett Chrome OS Internals LinuxCon Europe 2014 11 / 43 Updates Chrome OS downloads and installs signed updates from Google Includes new firmware, kernel, and OS root Chrome OS keeps an A and B firmware,
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