CVE-2025-40353

What it actually does

Spurious WARN_ON_ONCE triggered in arm64 copy_highpage() when PG_mte_tagged flag is already set on a destination page during repeated folio_mc_copy calls after migration failure.

Why it matters to the business

Kernel log noise and potential false-positive alerts on Red Hat Enterprise Linux 7.3 systems; no data loss, privilege escalation, or service disruption risk.

How an attack unfolds

No attacker exploitation path exists; the change eliminates an incorrect warning during legitimate kernel memory migration operations on arm64.

How to fix it

Update affected kernel packages to version 0:3.10.0-514.76.1.el7 or later on Red Hat rhel_aus and rhel_e4s 7.3 systems.

How to confirm the fix worked

Confirm package versions match or exceed the fixed releases and verify absence of the removed WARN_ON_ONCE in the copy_highpage() path after reboot.

How to detect it

Search kernel logs and dmesg for the original WARN_ON_ONCE string related to already-tagged pages; no post-exploitation artifacts exist.

What your security team should do

• Apply the listed kernel updates during the next maintenance window
• Monitor kernel logs for any remaining MTE-related warnings post-update
• Review EPSS trend and KEV status quarterly for this and similar arm64 memory tagging issues