CVE-2026-64229: x86/mm: Disable broadcast TLB flush when PCID is disabled
Greg Kroah-Hartman <[email protected]> Fri, 24 Jul 2026 17:23:32 +0200
| Newsgroups | org.kernel.vger.linux-cve-announce |
|---|---|
| Message-ID | <2026072418-CVE-2026-64229-0d1e@gregkh> |
From: Greg Kroah-Hartman <[email protected]> Description =========== In the Linux kernel, the following vulnerability has been resolved: x86/mm: Disable broadcast TLB flush when PCID is disabled Booting with "nopcid" clears X86_FEATURE_PCID and keeps CR4.PCIDE from being set to one. On AMD CPUs that support INVLPGB, broadcast TLB flushing remains enabled. There are two checks that decide whether the global ASID code runs, mm_global_asid() and consider_global_asid(), that key off of the X86_FEATURE_INVLPGB feature. Once an mm becomes active on more than three CPUs, consider_global_asid() assigns it a global ASID, after which flush_tlb_mm_range() takes the broadcast_tlb_flush() path using a non-zero PCID. Issuing an INVLPGB with a non-zero PCID while CR4.PCIDE is not set results in a #GP: Oops: general protection fault, kernel NULL pointer dereference 0x1: 0000 [#1] SMP NOPTI CPU: 158 UID: 0 PID: 3119 Comm: snap Not tainted 7.1.0-rc3 #1 PREEMPT(full) Hardware name: ... RIP: 0010:broadcast_tlb_flush Code: ... 89 da 48 83 c8 07 <0f> 01 fe eb 08 cc cc cc ... Call Trace: <TASK> flush_tlb_mm_range ptep_clear_flush wp_page_copy ? _raw_spin_unlock __handle_mm_fault handle_mm_fault do_user_addr_fault exc_page_fault asm_exc_page_fault All processors that support broadcast TLB invalidation also have PCID support, so it is only the "nopcid" scenario that is of concern. In this situation just disable the broadcast TLB support using the CPUID dependency support by making X86_FEATURE_INVLPGB dependent on X86_FEATURE_PCID. [ bp: Massage commit message. ] The Linux kernel CVE team has assigned CVE-2026-64229 to this issue. Affected and fixed versions =========================== Issue introduced in 6.15 with commit 4afeb0ed1753ebcad93ee3b45427ce85e9c8ec40 and fixed in 6.18.35 with commit fed725cace3ab1c4f7f8182e35029a603d953187 Issue introduced in 6.15 with commit 4afeb0ed1753ebcad93ee3b45427ce85e9c8ec40 and fixed in 7.0.11 with commit d2d6d21286719b454d5d87a8758c23d2377d88a2 Issue introduced in 6.15 with commit 4afeb0ed1753ebcad93ee3b45427ce85e9c8ec40 and fixed in 7.1 with commit 44126343d58c68adaa8343fbf1c07dd20078c35e Please see https://www.kernel.org for a full list of currently supported kernel versions by the kernel community. Unaffected versions might change over time as fixes are backported to older supported kernel versions. The official CVE entry at https://cve.org/CVERecord/?id=CVE-2026-64229 will be updated if fixes are backported, please check that for the most up to date information about this issue. Affected files ============== The file(s) affected by this issue are: arch/x86/kernel/cpu/cpuid-deps.c Mitigation ========== The Linux kernel CVE team recommends that you update to the latest stable kernel version for this, and many other bugfixes. Individual changes are never tested alone, but rather are part of a larger kernel release. Cherry-picking individual commits is not recommended or supported by the Linux kernel community at all. If however, updating to the latest release is impossible, the individual changes to resolve this issue can be found at these commits: https://git.kernel.org/stable/c/fed725cace3ab1c4f7f8182e35029a603d953187 https://git.kernel.org/stable/c/d2d6d21286719b454d5d87a8758c23d2377d88a2 https://git.kernel.org/stable/c/44126343d58c68adaa8343fbf1c07dd20078c35e