{"api_version":"1","generated_at":"2026-09-12T11:51:21+00:00","cve":"CVE-2026-89581","urls":{"html":"https://cve.report/CVE-2026-89581","api":"https://cve.report/api/cve/CVE-2026-89581.json","docs":"https://cve.report/api","cve_org":"https://www.cve.org/CVERecord?id=CVE-2026-89581","nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-89581"},"summary":{"title":"bpf, x86: Fix per-CPU address resolution into an extended register","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nbpf, x86: Fix per-CPU address resolution into an extended register\n\nThe destination of the per-CPU address MOV is encoded in ModRM.reg,\nwhich is extended by REX.R, but the REX prefix is built with\nadd_1mod(), which sets REX.B. REX.B extends ModRM.rm and SIB.base, and\nthis instruction addresses memory as disp32 with no base, so the bit\nhas no effect at all and the high register bit is simply lost.\n\nEvery is_ereg() destination therefore resolves to the wrong register,\npicking whichever one shares the low three bits:\n\n  R5 -> RAX    R7 -> RBP    R8 -> RSI    R9 -> RDI\n\nWith BPF_REG_5, whose reg2hex is 0, the emitted\n\n  65 49 03 04 25 <off>\tadd %gs:<off>,%rax\n\nadds the per-CPU offset to RAX rather than R8. The destination keeps\nthe unadjusted address and RAX is clobbered, so the program goes on to\ndereference a pointer that was never made per-CPU:\n\n  BUG: unable to handle page fault for address: 0000607e386a8894\n  RIP: bpf_prog_707837aafd2aa9ae_update_percpu_data+0x93/0xc9\n  Call Trace:\n   __bpf_prog_test_run_raw_tp+0x2dc/0x7d0\n   __flush_smp_call_function_queue+0x1e9/0xc80\n  Kernel panic - not syncing: Fatal exception in interrupt\n\nR5 is the mildest of the four, aliasing a scratch register and faulting\nat the store. R7 aliases RBP and would corrupt the frame pointer, R8\nand R9 alias the argument registers.\n\nUse add_2mod() so the register goes through REX.R, matching how\nadd_2reg() places it in ModRM.reg and how emit_priv_frame_ptr()\nhardcodes 0x4c for the same instruction with R9. Encodings for the\nnon-extended registers are unchanged.\n\nProblem showed up when trying to resurrect BPF_GCC CI (selftests built\nwith BPF_GCC).\n\nThis has gone unnoticed because clang reloads the address into R1\nbefore each per-CPU access, so the destination is never an extended\nregister. GCC keeps several per-CPU addresses live at once, and\ntest_progs-bpf_gcc panics the kernel in global_percpu_data/init, where\nthe address of a .percpu variable ends up in R5.","state":"PUBLISHED","assigner":"Linux","published_at":"2026-09-11 20:19:42","updated_at":"2026-09-11 20:19:42"},"problem_types":[],"metrics":[],"references":[{"url":"https://git.kernel.org/stable/c/6a19b18d458881bf3269a357cc6dc6db5eef4369","name":"https://git.kernel.org/stable/c/6a19b18d458881bf3269a357cc6dc6db5eef4369","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/6886642414f59f928728802dc2c972a9859e6310","name":"https://git.kernel.org/stable/c/6886642414f59f928728802dc2c972a9859e6310","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/5bbbce02e500d47d8e259a45be5a7be9741d0533","name":"https://git.kernel.org/stable/c/5bbbce02e500d47d8e259a45be5a7be9741d0533","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/638bc3aada8ecdece184d5c15b100d489c9cccd7","name":"https://git.kernel.org/stable/c/638bc3aada8ecdece184d5c15b100d489c9cccd7","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-89581","name":"CVE Program record","refsource":"CVE.ORG","tags":["canonical"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-89581","name":"NVD vulnerability detail","refsource":"NVD","tags":["canonical","analysis"]}],"affected":[{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 7bdbf7446305cb65c510c16d57cde82bc76b234a 638bc3aada8ecdece184d5c15b100d489c9cccd7 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 7bdbf7446305cb65c510c16d57cde82bc76b234a 6886642414f59f928728802dc2c972a9859e6310 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 7bdbf7446305cb65c510c16d57cde82bc76b234a 6a19b18d458881bf3269a357cc6dc6db5eef4369 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 7bdbf7446305cb65c510c16d57cde82bc76b234a 5bbbce02e500d47d8e259a45be5a7be9741d0533 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 6.10","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.10 semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.12.109 6.12.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.18.50 6.18.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 7.2.4 7.2.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 7.3-rc1 * original_commit_for_fix","platforms":[]}],"timeline":[],"solutions":[],"workarounds":[],"exploits":[],"credits":[],"nvd_cpes":[],"vendor_comments":[],"enrichments":{"kev":null,"epss":null,"legacy_qids":[]},"source_records":{"cve_program":{"containers":{"cna":{"affected":[{"defaultStatus":"unaffected","product":"Linux","programFiles":["arch/x86/net/bpf_jit_comp.c"],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","vendor":"Linux","versions":[{"lessThan":"638bc3aada8ecdece184d5c15b100d489c9cccd7","status":"affected","version":"7bdbf7446305cb65c510c16d57cde82bc76b234a","versionType":"git"},{"lessThan":"6886642414f59f928728802dc2c972a9859e6310","status":"affected","version":"7bdbf7446305cb65c510c16d57cde82bc76b234a","versionType":"git"},{"lessThan":"6a19b18d458881bf3269a357cc6dc6db5eef4369","status":"affected","version":"7bdbf7446305cb65c510c16d57cde82bc76b234a","versionType":"git"},{"lessThan":"5bbbce02e500d47d8e259a45be5a7be9741d0533","status":"affected","version":"7bdbf7446305cb65c510c16d57cde82bc76b234a","versionType":"git"}]},{"defaultStatus":"affected","product":"Linux","programFiles":["arch/x86/net/bpf_jit_comp.c"],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","vendor":"Linux","versions":[{"status":"affected","version":"6.10"},{"lessThan":"6.10","status":"unaffected","version":"0","versionType":"semver"},{"lessThanOrEqual":"6.12.*","status":"unaffected","version":"6.12.109","versionType":"semver"},{"lessThanOrEqual":"6.18.*","status":"unaffected","version":"6.18.50","versionType":"semver"},{"lessThanOrEqual":"7.2.*","status":"unaffected","version":"7.2.4","versionType":"semver"},{"lessThanOrEqual":"*","status":"unaffected","version":"7.3-rc1","versionType":"original_commit_for_fix"}]}],"cpeApplicability":[{"nodes":[{"cpeMatch":[{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.12.109","versionStartIncluding":"6.10","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.18.50","versionStartIncluding":"6.10","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"7.2.4","versionStartIncluding":"6.10","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"7.3-rc1","versionStartIncluding":"6.10","vulnerable":true}],"negate":false,"operator":"OR"}]}],"descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nbpf, x86: Fix per-CPU address resolution into an extended register\n\nThe destination of the per-CPU address MOV is encoded in ModRM.reg,\nwhich is extended by REX.R, but the REX prefix is built with\nadd_1mod(), which sets REX.B. REX.B extends ModRM.rm and SIB.base, and\nthis instruction addresses memory as disp32 with no base, so the bit\nhas no effect at all and the high register bit is simply lost.\n\nEvery is_ereg() destination therefore resolves to the wrong register,\npicking whichever one shares the low three bits:\n\n  R5 -> RAX    R7 -> RBP    R8 -> RSI    R9 -> RDI\n\nWith BPF_REG_5, whose reg2hex is 0, the emitted\n\n  65 49 03 04 25 <off>\tadd %gs:<off>,%rax\n\nadds the per-CPU offset to RAX rather than R8. The destination keeps\nthe unadjusted address and RAX is clobbered, so the program goes on to\ndereference a pointer that was never made per-CPU:\n\n  BUG: unable to handle page fault for address: 0000607e386a8894\n  RIP: bpf_prog_707837aafd2aa9ae_update_percpu_data+0x93/0xc9\n  Call Trace:\n   __bpf_prog_test_run_raw_tp+0x2dc/0x7d0\n   __flush_smp_call_function_queue+0x1e9/0xc80\n  Kernel panic - not syncing: Fatal exception in interrupt\n\nR5 is the mildest of the four, aliasing a scratch register and faulting\nat the store. R7 aliases RBP and would corrupt the frame pointer, R8\nand R9 alias the argument registers.\n\nUse add_2mod() so the register goes through REX.R, matching how\nadd_2reg() places it in ModRM.reg and how emit_priv_frame_ptr()\nhardcodes 0x4c for the same instruction with R9. Encodings for the\nnon-extended registers are unchanged.\n\nProblem showed up when trying to resurrect BPF_GCC CI (selftests built\nwith BPF_GCC).\n\nThis has gone unnoticed because clang reloads the address into R1\nbefore each per-CPU access, so the destination is never an extended\nregister. GCC keeps several per-CPU addresses live at once, and\ntest_progs-bpf_gcc panics the kernel in global_percpu_data/init, where\nthe address of a .percpu variable ends up in R5."}],"providerMetadata":{"dateUpdated":"2026-09-11T19:44:47.581Z","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux"},"references":[{"url":"https://git.kernel.org/stable/c/638bc3aada8ecdece184d5c15b100d489c9cccd7"},{"url":"https://git.kernel.org/stable/c/6886642414f59f928728802dc2c972a9859e6310"},{"url":"https://git.kernel.org/stable/c/6a19b18d458881bf3269a357cc6dc6db5eef4369"},{"url":"https://git.kernel.org/stable/c/5bbbce02e500d47d8e259a45be5a7be9741d0533"}],"title":"bpf, x86: Fix per-CPU address resolution into an extended register","x_generator":{"engine":"bippy-1.2.0"}}},"cveMetadata":{"assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","assignerShortName":"Linux","cveId":"CVE-2026-89581","datePublished":"2026-09-11T19:44:47.581Z","dateReserved":"2026-09-11T19:38:34.728Z","dateUpdated":"2026-09-11T19:44:47.581Z","state":"PUBLISHED"},"dataType":"CVE_RECORD","dataVersion":"5.2"},"nvd":{"publishedDate":"2026-09-11 20:19:42","lastModifiedDate":"2026-09-11 20:19:42","problem_types":[],"metrics":[],"configurations":[]},"legacy_mitre":{"record":{"CveYear":"2026","CveId":"89581","Ordinal":"1","Title":"bpf, x86: Fix per-CPU address resolution into an extended regist","CVE":"CVE-2026-89581","Year":"2026"},"notes":[{"CveYear":"2026","CveId":"89581","Ordinal":"1","NoteData":"In the Linux kernel, the following vulnerability has been resolved:\n\nbpf, x86: Fix per-CPU address resolution into an extended register\n\nThe destination of the per-CPU address MOV is encoded in ModRM.reg,\nwhich is extended by REX.R, but the REX prefix is built with\nadd_1mod(), which sets REX.B. REX.B extends ModRM.rm and SIB.base, and\nthis instruction addresses memory as disp32 with no base, so the bit\nhas no effect at all and the high register bit is simply lost.\n\nEvery is_ereg() destination therefore resolves to the wrong register,\npicking whichever one shares the low three bits:\n\n  R5 -> RAX    R7 -> RBP    R8 -> RSI    R9 -> RDI\n\nWith BPF_REG_5, whose reg2hex is 0, the emitted\n\n  65 49 03 04 25 <off>\tadd %gs:<off>,%rax\n\nadds the per-CPU offset to RAX rather than R8. The destination keeps\nthe unadjusted address and RAX is clobbered, so the program goes on to\ndereference a pointer that was never made per-CPU:\n\n  BUG: unable to handle page fault for address: 0000607e386a8894\n  RIP: bpf_prog_707837aafd2aa9ae_update_percpu_data+0x93/0xc9\n  Call Trace:\n   __bpf_prog_test_run_raw_tp+0x2dc/0x7d0\n   __flush_smp_call_function_queue+0x1e9/0xc80\n  Kernel panic - not syncing: Fatal exception in interrupt\n\nR5 is the mildest of the four, aliasing a scratch register and faulting\nat the store. R7 aliases RBP and would corrupt the frame pointer, R8\nand R9 alias the argument registers.\n\nUse add_2mod() so the register goes through REX.R, matching how\nadd_2reg() places it in ModRM.reg and how emit_priv_frame_ptr()\nhardcodes 0x4c for the same instruction with R9. Encodings for the\nnon-extended registers are unchanged.\n\nProblem showed up when trying to resurrect BPF_GCC CI (selftests built\nwith BPF_GCC).\n\nThis has gone unnoticed because clang reloads the address into R1\nbefore each per-CPU access, so the destination is never an extended\nregister. GCC keeps several per-CPU addresses live at once, and\ntest_progs-bpf_gcc panics the kernel in global_percpu_data/init, where\nthe address of a .percpu variable ends up in R5.","Type":"Description","Title":"bpf, x86: Fix per-CPU address resolution into an extended regist"}]}}}