# CVE-2023-53742: kcsan: Avoid READ_ONCE() in read_instrumented_memory()

> A kernel bug in KCSAN instrumentation causes a null pointer dereference during memory reads, leading to a system crash.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Not stated
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 8 Dec 2025
- **Updated:** 11 May 2026
- **Also known as:** BELL-CVE-2023-53742, DEBIAN-CVE-2023-53742, GHSA-phff-w2xw-v2wg, ROOT-OS-DEBIAN-11-CVE-2023-53742, ROOT-OS-UBUNTU-2204-CVE-2023-53742, UBUNTU-CVE-2023-53742

## What is CVE-2023-53742?

CVE-2023-53742 is a vulnerability in Linux, published on 8 Dec 2025. 

### Official description

In the Linux kernel, the following vulnerability has been resolved:

kcsan: Avoid READ_ONCE() in read_instrumented_memory()

Haibo Li reported:

 | Unable to handle kernel paging request at virtual address
 |   ffffff802a0d8d7171
 | Mem abort info:o:
 |   ESR = 0x9600002121
 |   EC = 0x25: DABT (current EL), IL = 32 bitsts
 |   SET = 0, FnV = 0 0
 |   EA = 0, S1PTW = 0 0
 |   FSC = 0x21: alignment fault
 | Data abort info:o:
 |   ISV = 0, ISS = 0x0000002121
 |   CM = 0, WnR = 0 0
 | swapper pgtable: 4k pages, 39-bit VAs, pgdp=000000002835200000
 | [ffffff802a0d8d71] pgd=180000005fbf9003, p4d=180000005fbf9003,
 | pud=180000005fbf9003, pmd=180000005fbe8003, pte=006800002a0d8707
 | Internal error: Oops: 96000021 [#1] PREEMPT SMP
 | Modules linked in:
 | CPU: 2 PID: 45 Comm: kworker/u8:2 Not tainted
 |   5.15.78-android13-8-g63561175bbda-dirty #1
 | ...
 | pc : kcsan_setup_watchpoint+0x26c/0x6bc
 | lr : kcsan_setup_watchpoint+0x88/0x6bc
 | sp : ffffffc00ab4b7f0
 | x29: ffffffc00ab4b800 x28: ffffff80294fe588 x27: 0000000000000001
 | x26: 0000000000000019 x25: 0000000000000001 x24: ffffff80294fdb80
 | x23: 0000000000000000 x22: ffffffc00a70fb68 x21: ffffff802a0d8d71
 | x20: 0000000000000002 x19: 0000000000000000 x18: ffffffc00a9bd060
 | x17: 0000000000000001 x16: 0000000000000000 x15: ffffffc00a59f000
 | x14: 0000000000000001 x13: 0000000000000000 x12: ffffffc00a70faa0
 | x11: 00000000aaaaaaab x10: 0000000000000054 x9 : ffffffc00839adf8
 | x8 : ffffffc009b4cf00 x7 : 0000000000000000 x6 : 0000000000000007
 | x5 : 0000000000000000 x4 : 0000000000000000 x3 : ffffffc00a70fb70
 | x2 : 0005ff802a0d8d71 x1 : 0000000000000000 x0 : 0000000000000000
 | Call trace:
 |  kcsan_setup_watchpoint+0x26c/0x6bc
 |  __tsan_read2+0x1f0/0x234
 |  inflate_fast+0x498/0x750
 |  zlib_inflate+0x1304/0x2384
 |  __gunzip+0x3a0/0x45c
 |  gunzip+0x20/0x30
 |  unpack_to_rootfs+0x2a8/0x3fc
 |  do_populate_rootfs+0xe8/0x11c
 |  async_run_entry_fn+0x58/0x1bc
 |  process_one_work+0x3ec/0x738
 |  worker_thread+0x4c4/0x838
 |  kthread+0x20c/0x258
 |  ret_from_fork+0x10/0x20
 | Code: b8bfc2a8 2a0803f7 14000007 d503249f (78bfc2a8) )
 | ---[ end trace 613a943cb0a572b6 ]-----

The reason for this is that on certain arm64 configuration since
e35123d83ee3 ("arm64: lto: Strengthen READ_ONCE() to acquire when
CONFIG_LTO=y"), READ_ONCE() may be promoted to a full atomic acquire
instruction which cannot be used on unaligned addresses.

Fix it by avoiding READ_ONCE() in read_instrumented_memory(), and simply
forcing the compiler to do the required access by casting to the
appropriate volatile type. In terms of generated code this currently
only affects architectures that do not use the default READ_ONCE()
implementation.

The only downside is that we are not guaranteed atomicity of the access
itself, although on most architectures a plain load up to machine word
size should still be atomic (a fact the default READ_ONCE() still relies
on itself).

## Which versions are affected by CVE-2023-53742?


## How do I fix CVE-2023-53742?

Apply the vendor's patch.

## Is CVE-2023-53742 being exploited?

There is no known exploitation of CVE-2023-53742 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2023-53742 and fix it if it is affected.

What it is: CVE-2023-53742 is a vulnerability in Linux, published on 8 Dec 2025. 
Exploitation: There is no known exploitation of CVE-2023-53742 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2023-53742/ (Markdown: https://insights.sbomify.com/CVE-2023-53742/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2023-53742
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-53742
- OSV: https://osv.dev/vulnerability/CVE-2023-53742

---
From sbomify Insights: https://insights.sbomify.com/CVE-2023-53742/
Summaries are generated and may contain mistakes; the official description above is the record.