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Maciej W. Rozycki 7fb13fd351 MIPS: DEC: Prevent initial console buffer from landing in XKPHYS
In 64-bit configurations calling the initial console output handler from
a kernel thread other than the initial one will result in a situation
where the stack has been placed in the XKPHYS 64-bit memory segment and
consequently so has been the buffer allocated there that is used as the
argument corresponding to the `%s' output conversion specifier for the
firmware's printf() entry point.

This 64-bit address will then be truncated by 32-bit firmware, resulting
in an attempt to access the wrong memory location, which in turn will
cause all kinds of unpredictable behaviour, such as a kernel crash:

  Console: colour dummy device 160x64
  Calibrating delay loop... 49.36 BogoMIPS (lpj=192512)
  pid_max: default: 32768 minimum: 301
  CPU 0 Unable to handle kernel paging request at virtual address 000000000203bd00, epc == ffffffffbfc08364, ra == ffffffffbfc08800
  Oops[#1]:
  CPU: 0 PID: 0 Comm: swapper Not tainted 5.18.0-rc2-00254-gfb649bda6f56-dirty #121
  $ 0   : 0000000000000000 0000000000000001 0000000000000023 ffffffff80684ba0
  $ 4   : 000000000203bd00 ffffffffbfc0f3b4 ffffffffffffffff 0000000000000073
  $ 8   : 0a303d7469000000 0000000000000000 0000000000000073 ffffffffbfc0f473
  $12   : 0000000000000002 0000000000000000 ffffffff80684c1c 0000000000000000
  $16   : 0000000000000000 ffffffff80596dc9 0000000000000000 ffffffffbfc09240
  $20   : ffffffff80684c40 ffffffffbfc0f400 000000000000002d 000000000000002b
  $24   : ffffffffffffffbf 000000000203bd00
  $28   : ffffffff805f0000 ffffffff80684b58 0000000000000030 ffffffffbfc08800
  Hi    : 0000000000000000
  Lo    : 0000000000000aa8
  epc   : ffffffffbfc08364 0xffffffffbfc08364
  ra    : ffffffffbfc08800 0xffffffffbfc08800
  Status: 140120e2        KX SX UX KERNEL EXL
  Cause : 00000008 (ExcCode 02)
  BadVA : 000000000203bd00
  PrId  : 00000430 (R4000SC)
  Modules linked in:
  Process swapper (pid: 0, threadinfo=(____ptrval____), task=(____ptrval____), tls=0000000000000000)
  Stack : 0000000000000000 0000000000000000 0000000000000000 0000004d0000004d
          80684cc0806a2a40 80596dc80000004d 8061000000000000 bfc0850c80684c38
          0000000000000000 000000000203bd00 0000000000000000 0000000000000000
          0000000000000000 00000000bfc0f3b4 0000000000000000 0000000000000000
          0000000000000000 0000000000000000 0000000000000000 0000000000000000
          0000000000000000 0000000000000000 0000000000000000 0000000000000000
          0000002500000000 0000000000000000 0000000000000000 802c1a7400000000
          0203bd0080596dc8 0203bd4d69000000 6c61632000000018 5f746567646e6172
          6c616320625f6d6f 5f736e5f6d6f7266 206361323778302b 303d74696e726320
          806a0a38806b0000 806a0a38806b0000 00000000806b0000 80683c58806b0000
          ...
  Call Trace:

  Code: a082ffff  03e00008  00601021 <80820000> 00001821  10400005  24840001  80820000  24630001

  ---[ end trace 0000000000000000 ]---
  Kernel panic - not syncing: Fatal exception in interrupt

  KN04 V2.1k    (PC: 0xa0026768, SP: 0x806848e8)
  >>

In this case the pointer in $4 was truncated from 0x980000000203bd00 to
0x000000000203bd00.

This may happen when no final console driver has been enabled in the
configuration and consequently the initial console continues being used
late into bootstrap or with an upcoming change that will switch the zs
driver to use a platform device, which in turn will make the console
handover happen only after other kernel threads have already been
started.

Fix the issue by making the buffer static and initdata, and therefore
placed in the CKSEG0 32-bit compatibility segment, observing that the
console output handler is called with the console lock held, implying
no need for this code to be reentrant.  Add an assertion to verify the
buffer actually has been placed in a compatibility segment.

Fixes: 1da177e4c3 ("Linux-2.6.12-rc2")
Signed-off-by: Maciej W. Rozycki <macro@orcam.me.uk>
Cc: stable@vger.kernel.org # v2.6.12+
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
2026-05-26 16:35:36 +02:00
arch MIPS: DEC: Prevent initial console buffer from landing in XKPHYS 2026-05-26 16:35:36 +02:00
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 drm fixes for 7.1-rc5 2026-05-22 16:15:32 -07:00
drivers Miscellaneous x86 fixes: 2026-05-24 11:00:45 -07:00
fs three ksmbd server fixes 2026-05-23 16:59:02 -07:00
include bpf-fixes 2026-05-24 09:53:17 -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-fixes 2026-05-24 09:53:17 -07:00
lib Debugobjects fix: 2026-05-24 10:48:55 -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 Including fixes from Bluetooth, wireless and netfilter. 2026-05-21 14:39:12 -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 Arm: 2026-05-24 12:50:36 -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 myself 2026-04-02 16:48:25 +02:00
.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
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 NIOS2: updates for v7.2 2026-05-23 09:21:08 -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