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Woojin Ji says: ==================== bpf: Preserve scalar zero spills for stack reads Changes in v3: - Apply scalar-zero spill preservation to fixed-offset mixed stack reads as well. - Remove the var-offset-only flag from mark_reg_stack_read(). - Keep pure register-fill behavior unchanged. - Add fixed-offset mixed zero/spill-zero selftest coverage. - Address selftest nits: drop extra unpriv checks, align asm formatting, and remove the pruning-sensitive test. - Link to v2: https://patch.msgid.link/20260613-bpf-stack-var-off-zero-v1-v2-0-a324af0f00ea@gmail.com Stack reads currently lose the known-zero fact when loaded bytes come from a spilled scalar constant zero rather than from STACK_ZERO bytes in some paths. This series teaches the stack read zero reconstruction path to preserve that fact while marking the contributing spill slots precise. The original reproducer used a variable-offset stack byte read emitted by clang 22.1.6 at -O2/-O3 from a small helper-based BPF C program. Review of v2 pointed out that fixed-offset reads can benefit as well: pure scalar zero spill reads were already handled, but a fixed read spanning both STACK_ZERO and scalar const-zero STACK_SPILL bytes, e.g. 0000ssss, still fell back to an unknown scalar. v3 handles that mixed fixed-offset case without changing the existing pure register-fill behavior. I still do not have a confirmed deployed-program regression, so this stays targeted at bpf-next. Tested with: - make O=../../out/kernel olddefconfig - make O=../../out/kernel -j$(nproc) kernel/bpf/verifier.o - make O=../../out/kernel LLVM=1 -j$(nproc) bzImage - make -C tools/testing/selftests/bpf O=../../../../../out/kernel VMLINUX_BTF=../../../../../out/kernel/vmlinux TEST_KMOD_TARGETS= LLVM=1 -j$(nproc) test_progs - QEMU guest: ./test_progs -t verifier_var_off -v Summary: 1/24 PASSED, 0 SKIPPED, 0 FAILED - QEMU guest: ./test_progs -t verifier_spill_fill -t verifier_live_stack -t verifier_search_pruning -v Summary: 3/128 PASSED, 0 SKIPPED, 0 FAILED - QEMU guest: ./veristat -o csv verifier_var_off.bpf.o verifier_spill_fill.bpf.o Assisted-by: opencode:gpt-5.5 Signed-off-by: Woojin Ji <random6.xyz@gmail.com> --- ==================== Link: https://patch.msgid.link/20260625-bpf-stack-var-off-zero-v1-v3-0-a068210a761b@gmail.com Signed-off-by: Alexei Starovoitov <ast@kernel.org> |
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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. 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