Bug 2422712 (CVE-2025-40353)

Summary: CVE-2025-40353 kernel: arm64: mte: Do not warn if the page is already tagged in copy_highpage()
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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Priority: medium    
Version: unspecifiedKeywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel’s arm64 copy_highpage() implementation related to Memory Tagging Extensionflag handling. The function previously assumed that a destination page for a copy operation would always be newly allocated and untagged. Under certain memory migration paths, this assumption no longer holds, and copy_highpage() could generate extraneous WARN_ON_ONCE() messages if the page was already MTE-tagged.
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Description OSIDB Bzimport 2025-12-16 14:05:42 UTC
In the Linux kernel, the following vulnerability has been resolved:

arm64: mte: Do not warn if the page is already tagged in copy_highpage()

The arm64 copy_highpage() assumes that the destination page is newly
allocated and not MTE-tagged (PG_mte_tagged unset) and warns
accordingly. However, following commit 060913999d7a ("mm: migrate:
support poisoned recover from migrate folio"), folio_mc_copy() is called
before __folio_migrate_mapping(). If the latter fails (-EAGAIN), the
copy will be done again to the same destination page. Since
copy_highpage() already set the PG_mte_tagged flag, this second copy
will warn.

Replace the WARN_ON_ONCE(page already tagged) in the arm64
copy_highpage() with a comment.