ARM: 9485/1: mm: acquire mmap write lock around show_pte() for user faultsgrafted

When CONFIG_DEBUG_USER=y, and cmdline "user_debug=31" is set,
a user fault may trigger show_pte() without any lock.
If another thread in the same process concurrently calls munmap(),
the page table pages may be freed while show_pte() is still traversing
them, causing a use-after-free in show_pte().

If CONFIG_ARM_LPAE=y, this may cause a kernel panic if the pages table
of PMD are freed when show_pte() is running.

Acquire mmap_write_lock() around show_pte() for user faults to fix the
contention.

For user faults, additionally restrict that show_pte() is called only
when the addr is a user-space address (addr < TASK_SIZE). This is because
the lock of tsk->mm only protects the virtual memory of user address space,
furthermore, dumping the page tables of a kernel-space address for user
faults is unnecessary and may have security implications.

Keep everything unchanged for kernel faults, because the kernel is
already in the "oops" state, acquiring a lock may risk a deadlock.

Co-developed-by: Qi Xi <xiqi2@huawei.com>

Fixes: 6d021b724481 ("ARM: dump pgd, pmd and pte states on unhandled data abort faults")
Link: https://lore.kernel.org/20260716014022.2823-1-xieyuanbin1@huawei.com
Acked-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Reviewed-by: Linus Walleij <linusw@kernel.org>
Signed-off-by: Qi Xi <xiqi2@huawei.com>
Signed-off-by: Xie Yuanbin <xieyuanbin1@huawei.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>

1 files changed, 109 insertions, 0 deletions

diff --git a/Documentation/process/generated-content.rst b/Documentation/process/generated-content.rst
new file mode 100644
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+++ b/Documentation/process/generated-content.rst
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+============================================
+Kernel Guidelines for Tool-Generated Content
+============================================
+
+Purpose
+=======
+
+Kernel contributors have been using tooling to generate contributions
+for a long time. These tools can increase the volume of contributions.
+At the same time, reviewer and maintainer bandwidth is a scarce
+resource. Understanding which portions of a contribution come from
+humans versus tools is helpful to maintain those resources and keep
+kernel development healthy.
+
+The goal here is to clarify community expectations around tools. This
+lets everyone become more productive while also maintaining high
+degrees of trust between submitters and reviewers.
+
+Out of Scope
+============
+
+These guidelines do not apply to tools that make trivial tweaks to
+preexisting content. Nor do they pertain to tooling that helps with
+menial tasks. Some examples:
+
+ - Spelling and grammar fix ups, like rephrasing to imperative voice
+ - Typing aids like identifier completion, common boilerplate or
+   trivial pattern completion
+ - Purely mechanical transformations like variable renaming
+ - Reformatting, like running Lindent, ``clang-format`` or
+   ``rust-fmt``
+
+Even whenever your tool use is out of scope, you should still always
+consider if it would help reviewing your contribution if the reviewer
+knows about the tool that you used.
+
+In Scope
+========
+
+These guidelines apply when a meaningful amount of content in a kernel
+contribution was not written by a person in the Signed-off-by chain,
+but was instead created by a tool.
+
+Detection of a problem and testing the fix for it is also part of the
+development process; if a tool was used to find a problem addressed by
+a change, that should be noted in the changelog. This not only gives
+credit where it is due, it also helps fellow developers find out about
+these tools.
+
+Some examples:
+ - Any tool-suggested fix such as ``checkpatch.pl --fix``
+ - Coccinelle scripts
+ - A chatbot generated a new function in your patch to sort list entries.
+ - A .c file in the patch was originally generated by a coding
+   assistant but cleaned up by hand.
+ - The changelog was generated by handing the patch to a generative AI
+   tool and asking it to write the changelog.
+ - The changelog was translated from another language.
+
+If in doubt, choose transparency and assume these guidelines apply to
+your contribution.
+
+Guidelines
+==========
+
+First, read the Developer's Certificate of Origin:
+Documentation/process/submitting-patches.rst. Its rules are simple
+and have been in place for a long time. They have covered many
+tool-generated contributions. Ensure that you understand your entire
+submission and are prepared to respond to review comments.
+
+Second, when making a contribution, be transparent about the origin of
+content in cover letters and changelogs. You can be more transparent
+by adding information like this:
+
+ - What tools were used?
+ - The input to the tools you used, like the Coccinelle source script.
+ - If code was largely generated from a single or short set of
+   prompts, include those prompts. For longer sessions, include a
+   summary of the prompts and the nature of resulting assistance.
+ - Which portions of the content were affected by that tool?
+ - How is the submission tested and what tools were used to test the
+   fix?
+
+As with all contributions, individual maintainers have discretion to
+choose how they handle the contribution. For example, they might:
+
+ - Treat it just like any other contribution.
+ - Reject it outright.
+ - Treat the contribution specially, for example, asking for extra
+   testing, reviewing with extra scrutiny, or reviewing at a lower
+   priority than human-generated content.
+ - Ask for some other special steps, like asking the contributor to
+   elaborate on how the tool or model was trained.
+ - Ask the submitter to explain in more detail about the contribution
+   so that the maintainer can be assured that the submitter fully
+   understands how the code works.
+ - Suggest a better prompt instead of suggesting specific code changes.
+
+If tools permit you to generate a contribution automatically, expect
+additional scrutiny in proportion to how much of it was generated.
+
+As with the output of any tooling, the result may be incorrect or
+inappropriate. You are expected to understand and to be able to defend
+everything you submit. If you are unable to do so, then do not submit
+the resulting changes.
+
+If you do so anyway, maintainers are entitled to reject your series
+without detailed review.