x86/mm: Eliminate window where TLB flushes may be inadvertently skipped

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2025-37964
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2025-05-20 16:15:34 UTC
Updated2026-07-14 13:17:34 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: x86/mm: Eliminate window where TLB flushes may be inadvertently skipped tl;dr: There is a window in the mm switching code where the new CR3 is set and the CPU should be getting TLB flushes for the new mm. But should_flush_tlb() has a bug and suppresses the flush. Fix it by widening the window where should_flush_tlb() sends an IPI. Long Version: === History === There were a few things leading up to this. First, updating mm_cpumask() was observed to be too expensive, so it was made lazier. But being lazy caused too many unnecessary IPIs to CPUs due to the now-lazy mm_cpumask(). So code was added to cull mm_cpumask() periodically[2]. But that culling was a bit too aggressive and skipped sending TLB flushes to CPUs that need them. So here we are again. === Problem === The too-aggressive code in should_flush_tlb() strikes in this window: // Turn on IPIs for this CPU/mm combination, but only // if should_flush_tlb() agrees: cpumask_set_cpu(cpu, mm_cpumask(next)); next_tlb_gen = atomic64_read(&next->context.tlb_gen); choose_new_asid(next, next_tlb_gen, &new_asid, &need_flush); load_new_mm_cr3(need_flush); // ^ After 'need_flush' is set to false, IPIs *MUST* // be sent to this CPU and not be ignored. this_cpu_write(cpu_tlbstate.loaded_mm, next); // ^ Not until this point does should_flush_tlb() // become true! should_flush_tlb() will suppress TLB flushes between load_new_mm_cr3() and writing to 'loaded_mm', which is a window where they should not be suppressed. Whoops. === Solution === Thankfully, the fuzzy "just about to write CR3" window is already marked with loaded_mm==LOADED_MM_SWITCHING. Simply checking for that state in should_flush_tlb() is sufficient to ensure that the CPU is targeted with an IPI. This will cause more TLB flush IPIs. But the window is relatively small and I do not expect this to cause any kind of measurable performance impact. Update the comment where LOADED_MM_SWITCHING is written since it grew yet another user. Peter Z also raised a concern that should_flush_tlb() might not observe 'loaded_mm' and 'is_lazy' in the same order that switch_mm_irqs_off() writes them. Add a barrier to ensure that they are observed in the order they are written.

Risk And Classification

Primary CVSS: v3.1 5.5 MEDIUM from [email protected]

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Problem Types: NVD-CWE-noinfo

CVSS v3.1 Breakdown

Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Operating System Linux Linux Kernel All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 848b5815177582de0e1d0118725378e0fbadca20 12f703811af043d32b1c8a30001b2fa04d5cd0ac git Not specified
CNA Linux Linux affected b47002ed65ade940839b7f439ff4a194e7d5ec28 02ad4ce144bd27f71f583f667fdf3b3ba0753477 git Not specified
CNA Linux Linux affected a04fe3bfc71e28009e20357b79df1e8ef7c9d600 d41072906abec8bb8e01ed16afefbaa558908c89 git Not specified
CNA Linux Linux affected 3dbe889a1b829b4c07e0836ff853fe649e51ce4f d87392094f96e162fa5fa5a8640d70cc0952806f git Not specified
CNA Linux Linux affected 6db2526c1d694c91c6e05e2f186c085e9460f202 399ec9ca8fc4999e676ff89a90184ec40031cf59 git Not specified
CNA Linux Linux affected 6db2526c1d694c91c6e05e2f186c085e9460f202 fea4e317f9e7e1f449ce90dedc27a2d2a95bee5a git Not specified
CNA Linux Linux affected d1347977661342cb09a304a17701eb2d4aa21dec git Not specified
CNA Linux Linux affected 5.15.179 5.15.183 semver Not specified
CNA Linux Linux affected 6.1.129 6.1.139 semver Not specified
CNA Linux Linux affected 6.6.79 6.6.91 semver Not specified
CNA Linux Linux affected 6.12.16 6.12.29 semver Not specified
CNA Linux Linux affected 6.13.4 6.14 semver Not specified
CNA Linux Linux affected 6.14 Not specified
CNA Linux Linux unaffected 6.14 semver Not specified
CNA Linux Linux unaffected 5.15.183 5.15.* semver Not specified
CNA Linux Linux unaffected 6.1.139 6.1.* semver Not specified
CNA Linux Linux unaffected 6.6.91 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.29 6.12.* semver Not specified
CNA Linux Linux unaffected 6.14.7 6.14.* semver Not specified
CNA Linux Linux unaffected 6.15 * original_commit_for_fix Not specified
ADP Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP affected V3.1.6 * custom Not specified
ADP Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP affected V3.1.6 * custom Not specified
ADP Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP affected V3.1.6 * custom Not specified
ADP Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP affected V3.1.6 * custom Not specified
ADP Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP affected V3.1.6 * custom Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/02ad4ce144bd27f71f583f667fdf3b3ba0753477 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/12f703811af043d32b1c8a30001b2fa04d5cd0ac 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
lists.debian.org/debian-lts-announce/2025/08/msg00010.html af854a3a-2127-422b-91ae-364da2661108 lists.debian.org Third Party Advisory
git.kernel.org/stable/c/399ec9ca8fc4999e676ff89a90184ec40031cf59 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
cert-portal.siemens.com/productcert/html/ssa-019113.html 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e cert-portal.siemens.com
git.kernel.org/stable/c/fea4e317f9e7e1f449ce90dedc27a2d2a95bee5a 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/d41072906abec8bb8e01ed16afefbaa558908c89 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/d87392094f96e162fa5fa5a8640d70cc0952806f 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
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