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Amery Hung 06d518a558 bpf: Preserve reg->id of pointer objects after null-check
Preserve reg->id of pointer objects after null-checking the register so
that children objects derived from it can still refer to it in the new
object relationship tracking mechanism introduced in a later patch. This
change incurs a slight increase in the number of states in one selftest
bpf object, rbtree_search.bpf.o. For Meta bpf objects, the increase of
states is also negligible.

Selftest BPF objects with insns_diff > 0

Program                   Insns (A)  Insns (B)  Insns   (DIFF)  States (A)  States (B)  States (DIFF)
------------------------  ---------  ---------  --------------  ----------  ----------  -------------
rbtree_search                  6820       7326   +506 (+7.42%)         379         398   +19 (+5.01%)

Meta BPF objects with insns_diff > 0

Program                   Insns (A)  Insns (B)  Insns   (DIFF)  States (A)  States (B)  States (DIFF)
------------------------  ---------  ---------  --------------  ----------  ----------  -------------
ned_imex_be_tclass               52         57     +5 (+9.62%)           5           6   +1 (+20.00%)
ned_imex_be_tclass               52         57     +5 (+9.62%)           5           6   +1 (+20.00%)
ned_skop_auto_flowlabel         523        526     +3 (+0.57%)          39          40    +1 (+2.56%)
ned_skop_mss                    289        292     +3 (+1.04%)          20          20    +0 (+0.00%)
ned_skopt_bet_classifier         78         82     +4 (+5.13%)           8           8    +0 (+0.00%)
dctcp_update_alpha              252        320   +68 (+26.98%)          21          27   +6 (+28.57%)
dctcp_update_alpha              252        320   +68 (+26.98%)          21          27   +6 (+28.57%)
ned_ts_func                     119        126     +7 (+5.88%)           6           7   +1 (+16.67%)
tw_egress                      1119       1128     +9 (+0.80%)          95          96    +1 (+1.05%)
tw_ingress                     1128       1137     +9 (+0.80%)          95          96    +1 (+1.05%)
tw_tproxy_router               4380       4465    +85 (+1.94%)         114         118    +4 (+3.51%)
tw_tproxy_router4              3093       3170    +77 (+2.49%)          83          88    +5 (+6.02%)
ttls_tc_ingress               34656      35717  +1061 (+3.06%)         936         970   +34 (+3.63%)
tw_twfw_egress               222327     222338    +11 (+0.00%)       10563       10564    +1 (+0.01%)
tw_twfw_ingress               78295      78299     +4 (+0.01%)        3825        3826    +1 (+0.03%)
tw_twfw_tc_eg                222839     222859    +20 (+0.01%)       10584       10585    +1 (+0.01%)
tw_twfw_tc_in                 78295      78299     +4 (+0.01%)        3825        3826    +1 (+0.03%)
tw_twfw_egress                 8080       8085     +5 (+0.06%)         456         456    +0 (+0.00%)
tw_twfw_ingress                8053       8056     +3 (+0.04%)         454         454    +0 (+0.00%)
tw_twfw_tc_eg                  8154       8174    +20 (+0.25%)         456         457    +1 (+0.22%)
tw_twfw_tc_in                  8060       8063     +3 (+0.04%)         455         455    +0 (+0.00%)
tw_twfw_egress               222327     222338    +11 (+0.00%)       10563       10564    +1 (+0.01%)
tw_twfw_ingress               78295      78299     +4 (+0.01%)        3825        3826    +1 (+0.03%)
tw_twfw_tc_eg                222839     222859    +20 (+0.01%)       10584       10585    +1 (+0.01%)
tw_twfw_tc_in                 78295      78299     +4 (+0.01%)        3825        3826    +1 (+0.03%)
tw_twfw_egress                 8080       8085     +5 (+0.06%)         456         456    +0 (+0.00%)
tw_twfw_ingress                8053       8056     +3 (+0.04%)         454         454    +0 (+0.00%)
tw_twfw_tc_eg                  8154       8174    +20 (+0.25%)         456         457    +1 (+0.22%)
tw_twfw_tc_in                  8060       8063     +3 (+0.04%)         455         455    +0 (+0.00%)

Looking into rbtree_search, the reason for such increase is that the
verifier has to explore the main loop shown below for one more iteration
until state pruning decides the current state is safe.

long rbtree_search(void *ctx)
{
	...
	bpf_spin_lock(&glock0);
	rb_n = bpf_rbtree_root(&groot0);
	while (can_loop) {
		if (!rb_n) {
			bpf_spin_unlock(&glock0);
			return __LINE__;
		}

		n = rb_entry(rb_n, struct node_data, r0);
		if (lookup_key == n->key0)
			break;
		if (nr_gc < NR_NODES)
			gc_ns[nr_gc++] = rb_n;
		if (lookup_key < n->key0)
			rb_n = bpf_rbtree_left(&groot0, rb_n);
		else
			rb_n = bpf_rbtree_right(&groot0, rb_n);
	}
	...
}

Below is what the verifier sees at the start of each iteration
(65: may_goto) after preserving id of rb_n. Without id of rb_n, the
verifier stops exploring the loop at iter 16.

           rb_n  gc_ns[15]
iter 15    257   257

iter 16    290   257    rb_n: idmap add 257->290
                        gc_ns[15]: check 257 != 290 --> state not equal

iter 17    325   257    rb_n: idmap add 290->325
                        gc_ns[15]: idmap add 257->257 --> state safe

Acked-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Amery Hung <ameryhung@gmail.com>
Link: https://lore.kernel.org/r/20260529014936.2811085-5-ameryhung@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
2026-06-01 18:31:41 -07:00
arch bpf, arm64: Fix redundant MOV and clarify stack arg comments 2026-05-31 17:49:21 -07:00
block cgroup: Fixes for v7.1-rc4 2026-05-22 16:28:47 -07:00
certs Clang build fixes for 7.1 2026-04-24 09:29:51 -07:00
crypto crypto/krb5, rxrpc: Fix lack of pre-decrypt/pre-verify length checks 2026-05-20 16:36:45 -07:00
Documentation Merge branch 'arena_direct_access' 2026-05-25 08:35:48 -07:00
drivers Merge git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf 7.1-rc5 2026-05-25 06:33:30 -07:00
fs Merge git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf 7.1-rc5 2026-05-25 06:33:30 -07:00
include bpf: Unify dynptr handling in the verifier 2026-06-01 18:31:40 -07:00
init memblock: updates for 7.0-rc1 2026-04-18 11:29:14 -07:00
io_uring io_uring-7.1-20260522 2026-05-22 11:53:28 -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: Preserve reg->id of pointer objects after null-check 2026-06-01 18:31:41 -07:00
lib Merge git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf 7.1-rc5 2026-05-25 06:33:30 -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
mm cgroup: Fixes for v7.1-rc4 2026-05-22 16:28:47 -07:00
net Merge git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf 7.1-rc5 2026-05-25 06:33:30 -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 Second round of Kbuild fixes for 7.1 2026-05-19 09:43:24 -07:00
security lsm/stable-7.1 PR 20260519 2026-05-19 15:31:35 -05:00
sound ASoC: Fixes for v7.1 2026-05-22 08:25:18 +02:00
tools bpf: reject overlarge global subprog argument sizes 2026-05-31 17:50:14 -07:00
usr kbuild: uapi: also test UAPI headers against C++ compilers 2026-03-25 13:24:42 +01:00
virt KVM: Reject wrapped offset in kvm_reset_dirty_gfn() 2026-05-12 22:16:16 +02:00
.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 Including fixes from Bluetooth, wireless and netfilter. 2026-05-21 14:39:12 -07:00
.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 COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
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 bpf: Update bpf maintainers 2026-05-31 17:46:25 -07:00
Makefile Linux 7.1-rc5 2026-05-24 13:48:06 -07:00
README docs: add AI Coding Assistants documentation 2026-01-06 14:55:06 -07:00

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