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Richard Leitner 59eb22641f
spi: imx: fix slab corruption from undersized DMA bounce buffers
Since commit faa8e404ad ("spi: imx: support dynamic burst length for
ECSPI DMA mode"), the driver allocates its private DMA TX/RX buffers
with kzalloc(dma_len), where dma_len is only rounded up to 4 bytes, but
maps, syncs and unmaps them with DMA_CACHE_ALIGNED_LEN(dma_len), i.e.
rounded up to the cache line size. As a result, the DMA API operates on
memory beyond the end of the allocation.

This was observed on a custom i.MX8MP platform with an mcp251xfd CAN
controller under heavy RPMSG load, as a series of refcount_t warnings
triggered from rpmsg_recv_done() in virtio_rpmsg_bus:

  refcount_t: addition on 0; use-after-free.
  refcount_t: underflow; use-after-free.
  refcount_t: saturated; leaking memory.

Leading finally to an "Unable to handle kernel paging request" oops.
Reproducing this problem took between 30 minutes and roughly 30 hours
under the same workload.

Hardware watchpoints on the refcount of a struct rpmsg_endpoint showed
it was overwritten from 2 to 1 by __pi_memcpy_generic() in the
irq/155-spi2.0 thread. Additionally it was found that a "normal"
rpmsg_recv_done() took 11µs +/-2µs from its kref_get to kref_put. In
the error case the same sequence took about 215µs +/-10µs. Based on
this, an LLM was used to identify the size mismatch fixed here.

Allocate the buffers with DMA_CACHE_ALIGNED_LEN(dma_len) so they cover
the full mapped length, and use the same length for
dma_sync_single_for_cpu() to stay consistent with map and unmap.

With this patch applied, the same workload ran for more than 200 hours
without the problem reproducing.

Assisted-by: LLM
Fixes: faa8e404ad ("spi: imx: support dynamic burst length for ECSPI DMA mode")
Cc: stable@vger.kernel.org
Signed-off-by: Richard Leitner <richard.leitner@linux.dev>
Link: https://patch.msgid.link/20261015-fix-spi-imx-dma-v1-1-e28259671392@linux.dev
Signed-off-by: Mark Brown <broonie@kernel.org>
History 2026-10-15 22:26:02 +01:00
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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/


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============

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
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* System Administrator: Configuring and troubleshooting
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* 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
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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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=========================

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