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With all prerequisites in place select ARCH_SUPPORTS_CFI. Note that this support is supposed to work with the generic kCFI support which is provided by clang. This comes with a couple of limitations: The generic kCFI implementation does not generate a .kcfi_traps section, nor is a special instruction used in case a checksum mismatch is detected. This means in case of checksum mismatch the kernel just crashes. It should be quite easy to tell by the surrounding code that a crash happened because of a checksum mismatch. If clang and/or gcc provide a .kcfi_traps section it will be possible to print proper CFI messages instead of just crashing the kernel (enable ARCH_USES_CFI_TRAPS). In addition this also means that CFI_PERMISSIVE does not work. Even if the option is selected the kernel will crash in case of checksum mismatch. However it seems to be acceptable to enable kCFI support to the kernel now even if it is not perfect. Later clang and gcc extensions are required to improve this. As of now a crash caused by a CFI failure looks like this: illegal operation: 0001 ilc:1 [#1]SMP Modules linked in: bpf_testmod(OE) CPU: 0 UID: 0 PID: 92 Comm: test_progs Tainted: G OE 7.2.0-rc4-00021-gc35ed7a1ca22-dirty #3 PREEMPTLAZY Tainted: [O]=OOT_MODULE, [E]=UNSIGNED_MODULE Hardware name: IBM 3931 A01 703 (KVM/Linux) Krnl PSW : 0704e00180000000 00000166d4853a0a (bpf_task_work_callback+0x176/0x290) R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:2 PM:0 RI:0 EA:3 Krnl GPRS: 0400000069b02e96 000001665471856c 0000000084dc1000 000000008084da58 000000008084da60 000000005ff492bf 0000000000000000 00000000809de300 fffffffffff7ffff 00000000000a0337 00000000809e4d00 000000008437b100 00000000801bc288 00000000801bc280 00000166d48538fc 000000e6d502ba90 Krnl Code: 00000166d48539fa: e320c0400004 lg %r2,64(%r12) 00000166d4853a00: e340c0480004 lg %r4,72(%r12) *00000166d4853a06: a7640001 brc 6,00000166d4853a08 >00000166d4853a0a: 0de1 basr %r14,%r1 00000166d4853a0c: e300b6580095 llh %r0,1624(%r11) 00000166d4853a12: ec040009027e cij %r0,2,4,00000166d4853a24 00000166d4853a18: a70affff ahi %r0,-1 00000166d4853a1c: 4000b658 sth %r0,1624(%r11) Call Trace: [<00000166d4853a0a>] bpf_task_work_callback+0x176/0x290 ... The disassembly contains the brc instruction (branch into the instruction itself with two byte offset to execute an illegal instruction, and the following basr instruction used for an indirect branch. Reviewed-by: Jens Remus <jremus@linux.ibm.com> Signed-off-by: Heiko Carstens <hca@linux.ibm.com> Tested-by: Nathan Chancellor <nathan@kernel.org> Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Linux kernel ============ The Linux kernel is the core of any Linux operating system. It manages hardware, system resources, and provides the fundamental services for all other software. Quick Start ----------- * Report a bug: See Documentation/admin-guide/reporting-issues.rst * Get the latest kernel: https://kernel.org * Build the kernel: See Documentation/admin-guide/quickly-build-trimmed-linux.rst * Join the community: https://lore.kernel.org/ Essential Documentation ----------------------- All users should be familiar with: * Building requirements: Documentation/process/changes.rst * Code of Conduct: Documentation/process/code-of-conduct.rst * License: See COPYING Documentation can be built with make htmldocs or viewed online at: https://www.kernel.org/doc/html/latest/ Who Are You? ============ Find your role below: * New Kernel Developer - Getting started with kernel development * Academic Researcher - Studying kernel internals and architecture * Security Expert - Hardening and vulnerability analysis * Backport/Maintenance Engineer - Maintaining stable kernels * System Administrator - Configuring and troubleshooting * Maintainer - Leading subsystems and reviewing patches * Hardware Vendor - Writing drivers for new hardware * Distribution Maintainer - Packaging kernels for distros * AI Coding Assistant - LLMs and AI-powered development tools For Specific Users ================== New Kernel Developer -------------------- Welcome! Start your kernel development journey here: * Getting Started: Documentation/process/development-process.rst * Your First Patch: Documentation/process/submitting-patches.rst * Coding Style: Documentation/process/coding-style.rst * Build System: Documentation/kbuild/index.rst * Development Tools: Documentation/dev-tools/index.rst * Kernel Hacking Guide: Documentation/kernel-hacking/hacking.rst * Core APIs: Documentation/core-api/index.rst Academic Researcher ------------------- Explore the kernel's architecture and internals: * Researcher Guidelines: Documentation/process/researcher-guidelines.rst * Memory Management: Documentation/mm/index.rst * Scheduler: Documentation/scheduler/index.rst * Networking Stack: Documentation/networking/index.rst * Filesystems: Documentation/filesystems/index.rst * RCU (Read-Copy Update): Documentation/RCU/index.rst * Locking Primitives: Documentation/locking/index.rst * Power Management: Documentation/power/index.rst Security Expert --------------- Security documentation and hardening guides: * Security Documentation: Documentation/security/index.rst * LSM Development: Documentation/security/lsm-development.rst * Self Protection: Documentation/security/self-protection.rst * Reporting Vulnerabilities: Documentation/process/security-bugs.rst * CVE Procedures: Documentation/process/cve.rst * Embargoed Hardware Issues: Documentation/process/embargoed-hardware-issues.rst * Security Features: Documentation/userspace-api/seccomp_filter.rst Backport/Maintenance Engineer ----------------------------- Maintain and stabilize kernel versions: * Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst * Backporting Guide: Documentation/process/backporting.rst * Applying Patches: Documentation/process/applying-patches.rst * Subsystem Profile: Documentation/maintainer/maintainer-entry-profile.rst * Git for Maintainers: Documentation/maintainer/configure-git.rst System Administrator -------------------- Configure, tune, and troubleshoot Linux systems: * Admin Guide: Documentation/admin-guide/index.rst * Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst * Sysctl Tuning: Documentation/admin-guide/sysctl/index.rst * Tracing/Debugging: Documentation/trace/index.rst * Performance Security: Documentation/admin-guide/perf-security.rst * Hardware Monitoring: Documentation/hwmon/index.rst Maintainer ---------- Lead kernel subsystems and manage contributions: * Maintainer Handbook: Documentation/maintainer/index.rst * Pull Requests: Documentation/maintainer/pull-requests.rst * Managing Patches: Documentation/maintainer/modifying-patches.rst * Rebasing and Merging: Documentation/maintainer/rebasing-and-merging.rst * Development Process: Documentation/process/maintainer-handbooks.rst * Maintainer Entry Profile: Documentation/maintainer/maintainer-entry-profile.rst * Git Configuration: Documentation/maintainer/configure-git.rst Hardware Vendor --------------- Write drivers and support new hardware: * Driver API Guide: Documentation/driver-api/index.rst * Driver Model: Documentation/driver-api/driver-model/driver.rst * Device Drivers: Documentation/driver-api/infrastructure.rst * Bus Types: Documentation/driver-api/driver-model/bus.rst * Device Tree Bindings: Documentation/devicetree/bindings/ * Power Management: Documentation/driver-api/pm/index.rst * DMA API: Documentation/core-api/dma-api.rst Distribution Maintainer ----------------------- Package and distribute the kernel: * Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst * ABI Documentation: Documentation/ABI/README * Kernel Configuration: Documentation/kbuild/kconfig.rst * Module Signing: Documentation/admin-guide/module-signing.rst * Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst * Tainted Kernels: Documentation/admin-guide/tainted-kernels.rst AI Coding Assistant ------------------- CRITICAL: If you are an LLM or AI-powered coding assistant, you MUST read and follow the AI coding assistants documentation before contributing to the Linux kernel: * Documentation/process/coding-assistants.rst This documentation contains essential requirements about licensing, attribution, and the Developer Certificate of Origin that all AI tools must comply with. Communication and Support ========================= * Mailing Lists: https://lore.kernel.org/ * IRC: #kernelnewbies on irc.oftc.net * Bugzilla: https://bugzilla.kernel.org/ * MAINTAINERS file: Lists subsystem maintainers and mailing lists * Email Clients: Documentation/process/email-clients.rst