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Yazhou Tang 58a8f3e250 bpf: Fix s16 truncation for large bpf-to-bpf call offsets
Currently, the BPF instruction set allows bpf-to-bpf calls (or internal
calls, pseudo calls) to use a 32-bit imm field to represent the relative
jump offset.

However, when JIT is disabled or falls back to the interpreter, the
verifier invokes bpf_patch_call_args() to rewrite the call instruction.
In this function, the 32-bit imm is downcast to s16 and stored in the off
field.

    void bpf_patch_call_args(struct bpf_insn *insn, u32 stack_depth)
    {
        stack_depth = max_t(u32, stack_depth, 1);
        insn->off = (s16) insn->imm;
        insn->imm = interpreters_args[(round_up(stack_depth, 32) / 32) - 1] -
            __bpf_call_base_args;
        insn->code = BPF_JMP | BPF_CALL_ARGS;
    }

If the original imm exceeds the s16 range (i.e., a jump offset greater
than 32767 instructions), this downcast silently truncates the offset,
resulting in an incorrect call target.

Fix this by:
1. In bpf_patch_call_args(), keeping the imm field unchanged and using the
   off field to store the index of the interpreter function.
2. In ___bpf_prog_run() for the JMP_CALL_ARGS case, retrieving the
   interpreter function pointer from the interpreters_args array using the
   off field as the index, and passing the original imm to calculate the
   last argument of the interpreter function.

After these changes, the truncation issue is resolved, and __bpf_call_base_args
is also no longer needed and can be removed, which makes the code cleaner.

Performance: In ___bpf_prog_run() for the JMP_CALL_ARGS case, changing the
retrieval of the interpreter function pointer from pointer addition to
direct array indexing improves performance. The possible reason is that the
latter has better instruction-level parallelism. See the v5 discussion [1]
for more details.

[1] https://lore.kernel.org/bpf/f120c3c4-6999-414a-b514-518bb64b4758@zju.edu.cn/

To avoid requiring bpftool changes, keep the new imm/off encoding internal
and restore the legacy xlated dump layout in bpf_insn_prepare_dump().
For bpf-to-bpf call offsets that do not fit in s16, export off as 0 instead
of a truncated and misleading value.

Fixes: 1ea47e01ad ("bpf: add support for bpf_call to interpreter")
Fixes: 7105e828c0 ("bpf: allow for correlation of maps and helpers in dump")
Suggested-by: Xu Kuohai <xukuohai@huaweicloud.com>
Suggested-by: Puranjay Mohan <puranjay@kernel.org>
Co-developed-by: Tianci Cao <ziye@zju.edu.cn>
Signed-off-by: Tianci Cao <ziye@zju.edu.cn>
Co-developed-by: Shenghao Yuan <shenghaoyuan0928@163.com>
Signed-off-by: Shenghao Yuan <shenghaoyuan0928@163.com>
Signed-off-by: Yazhou Tang <tangyazhou518@outlook.com>
Link: https://lore.kernel.org/r/20260506094714.419842-3-tangyazhou@zju.edu.cn
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
2026-05-11 08:27:02 -07:00
Documentation hwmon fixes for v7.1-rc3 2026-05-09 08:32:50 -07:00
LICENSES LICENSES: Add modern form of the LGPL-2.1 tags to the usage guide section 2025-10-22 07:58:19 +02:00
arch powerpc fixes for 7.1 #2 2026-05-09 08:03:21 -07:00
block block: only read from sqe on initial invocation of blkdev_uring_cmd() 2026-05-05 01:37:12 -06:00
certs Clang build fixes for 7.1 2026-04-24 09:29:51 -07:00
crypto This push contains the following changes: 2026-05-02 12:31:43 -07:00
drivers - Fix a string leak in the versalnet driver 2026-05-10 12:21:57 -07:00
fs fsverity fix for v7.1-rc3 2026-05-09 11:47:39 -07:00
include bpf: Fix s16 truncation for large bpf-to-bpf call offsets 2026-05-11 08:27:02 -07:00
init memblock: updates for 7.0-rc1 2026-04-18 11:29:14 -07:00
io_uring io_uring-7.1-20260508 2026-05-08 13:12:48 -07:00
ipc Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
kernel bpf: Fix s16 truncation for large bpf-to-bpf call offsets 2026-05-11 08:27:02 -07:00
lib fbdev fixes & cleanups for 7.1-rc3: 2026-05-05 14:25:44 -07:00
mm slab fixes for 7.1-rc1 2026-05-03 08:19:57 -07:00
net rxrpc: Also unshare DATA/RESPONSE packets when paged frags are present 2026-05-10 08:15:57 -07:00
rust Rust fixes for v7.1 2026-05-09 11:24:02 -07:00
samples soc: drivers for 7.1 2026-04-16 20:34:34 -07:00
scripts First round of Kbuild fixes for 7.1 2026-04-25 17:04:15 -07:00
security selinux: shrink critical section in sel_write_load() 2026-05-05 16:02:28 -04:00
sound ASoC: Fixes for v7.1 2026-05-06 16:10:00 +02:00
tools bpf-fixes 2026-05-09 18:42:54 -07:00
usr kbuild: uapi: also test UAPI headers against C++ compilers 2026-03-25 13:24:42 +01:00
virt Arm: 2026-04-17 07:18:03 -07:00
.clang-format Devicetree updates for v7.0: 2026-02-11 18:27:08 -08:00
.clippy.toml rust: bump Clippy's MSRV and clean `incompatible_msrv` allows 2026-04-07 09:51:39 +02:00
.cocciconfig
.editorconfig editorconfig: add rst extension 2026-01-26 19:07:09 -08:00
.get_maintainer.ignore .get_maintainer.ignore: add Askar 2026-04-15 02:15:02 -07:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore kbuild: rust: provide an option to inline C helpers into Rust 2026-03-30 02:03:52 +02:00
.mailmap MAINTAINERS: Update mail for Peter Rosin 2026-05-04 21:02:58 +02:00
.pylintrc docs: Move the python libraries to tools/lib/python 2025-11-18 09:22:40 -07:00
.rustfmt.toml rust: add `.rustfmt.toml` 2022-09-28 09:02:20 +02:00
COPYING
CREDITS Delete some obsolete networking code 2026-04-24 09:41:58 -07:00
Kbuild checksyscalls: move instance functionality into generic code 2026-04-05 09:21:32 +02:00
Kconfig io_uring: Rename KConfig to Kconfig 2025-02-19 14:53:27 -07:00
MAINTAINERS Fixes for clk drivers: 2026-05-10 08:10:47 -07:00
Makefile Linux 7.1-rc3 2026-05-10 14:08:09 -07:00
README docs: add AI Coding Assistants documentation 2026-01-06 14:55:06 -07:00

README

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