Bug 2467146 (CVE-2026-43258)

Summary: CVE-2026-43258 kernel: alpha: fix user-space corruption during memory compaction
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
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Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
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Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel, specifically affecting Alpha systems when memory compaction is enabled. Insufficient Translation Lookaside Buffer (TLB) shootdown during page migration can lead to sporadic user-space crashes and heap corruption. This vulnerability can result in application failures, including segmentation faults (SIGSEGV) and issues with memory allocation.
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Description OSIDB Bzimport 2026-05-06 13:06:50 UTC 
In the Linux kernel, the following vulnerability has been resolved:

alpha: fix user-space corruption during memory compaction

Alpha systems can suffer sporadic user-space crashes and heap
corruption when memory compaction is enabled.

Symptoms include SIGSEGV, glibc allocator failures (e.g. "unaligned
tcache chunk"), and compiler internal errors. The failures disappear
when compaction is disabled or when using global TLB invalidation.

The root cause is insufficient TLB shootdown during page migration.
Alpha relies on ASN-based MM context rollover for instruction cache
coherency, but this alone is not sufficient to prevent stale data or
instruction translations from surviving migration.

Fix this by introducing a migration-specific helper that combines:
  - MM context invalidation (ASN rollover),
  - immediate per-CPU TLB invalidation (TBI),
  - synchronous cross-CPU shootdown when required.

The helper is used only by migration/compaction paths to avoid changing
global TLB semantics.

Additionally, update flush_tlb_other(), pte_clear(), to use
READ_ONCE()/WRITE_ONCE() for correct SMP memory ordering.

This fixes observed crashes on both UP and SMP Alpha systems.
Comment 1 Keith Grant 2026-05-06 23:28:21 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026050606-CVE-2026-43258-a9be@gregkh/T