---
id: "CVE-2026-98923"
kind: "vulnerability"
aliases: ["CVE-2026-98923"]
title: "Linux arm64: spurious kernel warning when reading PROT_NONE mappings via /dev/mem"
severity: "unknown"
cvss: null
epss: 0.00209
exploited: false
status: "open"
category: "runtime"
products: []
ecosystems: []
tags: ["arm64", "kernel", "linux", "runtime"]
not_affected_if: ["no-dev-mem-access", "non-arm64"]
published_at: "2026-10-23T13:17:12+00:00"
first_seen_at: "2026-10-23T21:57:33+00:00"
updated_at: "2026-10-25T12:38:50+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-98923", "first_seen_at": "2026-10-23T21:57:33+00:00"}, {"source": "epss", "url": "https://api.first.org/data/v1/epss?cve=CVE-2026-98923", "first_seen_at": "2026-10-25T12:38:50+00:00"}]
---

# Linux arm64: spurious kernel warning when reading PROT_NONE mappings via /dev/mem

On arm64 Linux, mapping a page through /dev/mem with PROT_NONE and reading that process's /proc/<pid>/cmdline triggers a spurious kernel WARN in ioremap_prot(). The fix makes ioremap_prot() reject non-user protection values cleanly, so PROT_NONE and execute-only mappings can no longer be read through this path.

_Summary, check and fix written by a model from the sources; labelled as such._

## Timeline

- 2026-10-23T21:57:33+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-98923
- 2026-10-25T12:38:50+00:00 epss https://api.first.org/data/v1/epss?cve=CVE-2026-98923

## From the sources

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

arm64: io: Reject non-user protection in ioremap_prot()

Mapping a stack-top page via /dev/mem with PROT_NONE and then
reading that process's /proc/<pid>/cmdline triggers a spurious WARN
in ioremap_prot() through generic_access_phys():

  WARNING: ./arch/arm64/include/asm/io.h:275 at generic_access_phys
  Call trace:
    generic_access_phys+0x1c8/0x228 (P)
    __access_remote_vm+0x2b4/0x398
    access_remote_vm+0x14/0x30
    get_mm_cmdline+0xf8/0x2a0
    proc_pid_cmdline_read+0x68/0x120

generic_access_phys() passes the protection derived from the user PTE
to ioremap_prot(). On arm64, a PROT_NONE mapping is represented by a
present-invalid PTE, so pte_present() still returns true and the
protection reaches ioremap_prot().

A PROT_NONE mapping does not have PTE_USER, causing the existing
WARN_ON_ONCE() in ioremap_prot() to fire even though this is a valid
user mapping. Execute-only mappings have the same issue and must not
be readable through this path either.

ioremap_prot() should therefore reject protection values without
PTE_USER without warning. This makes the access fail cleanly for
PROT_NONE and execute-only mappings while retaining the existing
user-protection contract.

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_