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CVE-2025-37964
published 2025-05-20

CVE-2025-37964: In 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…

PriorityP420medium5.5CVSS 3.1
AVLACLPRLUINSUCNINAH
EPSS
0.16%
5.9th percentile
In 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_SWIT

Affected

30 ranges· showing 25
VendorProductVersion rangeFixed in
debiandebian_linux
debianlinux< linux 6.1.140-1 (bookworm)linux 6.1.140-1 (bookworm)
debianlinux-6.1< linux 6.1.140-1 (bookworm)linux 6.1.140-1 (bookworm)
linuxlinux
linuxlinux
linuxlinux>= 3dbe889a1b829b4c07e0836ff853fe649e51ce4f < d87392094f96e162fa5fa5a8640d70cc0952806fd87392094f96e162fa5fa5a8640d70cc0952806f
linuxlinux>= 5.15.179 < 5.15.1835.15.183
linuxlinux>= 6.1.129 < 6.1.1396.1.139
linuxlinux>= 6.12.16 < 6.12.296.12.29
linuxlinux>= 6.13.4 < 6.146.14
linuxlinux>= 6.6.79 < 6.6.916.6.91
linuxlinux>= 6db2526c1d694c91c6e05e2f186c085e9460f202 < 399ec9ca8fc4999e676ff89a90184ec40031cf59399ec9ca8fc4999e676ff89a90184ec40031cf59
linuxlinux>= 6db2526c1d694c91c6e05e2f186c085e9460f202 < fea4e317f9e7e1f449ce90dedc27a2d2a95bee5afea4e317f9e7e1f449ce90dedc27a2d2a95bee5a
linuxlinux>= 848b5815177582de0e1d0118725378e0fbadca20 < 12f703811af043d32b1c8a30001b2fa04d5cd0ac12f703811af043d32b1c8a30001b2fa04d5cd0ac
linuxlinux>= a04fe3bfc71e28009e20357b79df1e8ef7c9d600 < d41072906abec8bb8e01ed16afefbaa558908c89d41072906abec8bb8e01ed16afefbaa558908c89
linuxlinux>= b47002ed65ade940839b7f439ff4a194e7d5ec28 < 02ad4ce144bd27f71f583f667fdf3b3ba075347702ad4ce144bd27f71f583f667fdf3b3ba0753477
linuxlinux_kernel
linuxlinux_kernel
linuxlinux_kernel
linuxlinux_kernel
linuxlinux_kernel
linuxlinux_kernel>= 0 < 6.1.140-16.1.140-1
linuxlinux_kernel>= 0 < 6.12.29-16.12.29-1
linuxlinux_kernel>= 0 < 6.12.29-16.12.29-1
linuxlinux_kernel>= 0 < 5.15.0-144.1575.15.0-144.157

CVSS provenance

nvdv3.15.5MEDIUMCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
osv8.8HIGH
vendor_ubuntu8.8HIGH
vendor_debian5.5MEDIUM
vendor_redhat5.5MEDIUM
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