CVE-2026-89581
What it is
In the Linux kernel, the following vulnerability has been resolved: bpf, x86: Fix per-CPU address resolution into an extended register The destination of the per-CPU address MOV is encoded in ModRM.reg, which is extended by REX.R, but the REX prefix is built with add_1mod(), which sets REX.B. REX.B extends ModRM.rm and SIB.base, and this instruction addresses memory as disp32 with no base, so the bit has no effect at all and the high register bit is simply lost. Every is_ereg() destination therefore resolves to the wrong register, picking whichever one shares the low three bits: R5 -> RAX R7 -> RBP R8 -> RSI R9 -> RDI With BPF_REG_5, whose reg2hex is 0, the emitted 65 49 03 04 25 <off> add %gs:<off>,%rax adds the per-CPU offset to RAX rather than R8. The destination keeps the unadjusted address and RAX is clobbered, so the program goes on to dereference a pointer that was never made per-CPU: BUG: unable to handle page fault for address: 0000607e386a8894 RIP: bpf_prog_707837aafd2aa9ae_update_percpu_data+0x93/0xc9 Call Trace: __bpf_prog_test_run_raw_tp+0x2dc/0x7d0 __flush_smp_call_function_queue+0x1e9/0xc80 Kernel panic - not syncing: Fatal exception in interrupt R5 is the mildest of the four, aliasing a scratch register and faulting at the store. R7 aliases RBP and would corrupt the frame pointer, R8 and R9 alias the argument registers. Use add_2mod() so the register goes through REX.R, matching how add_2reg() places it in ModRM.reg and how emit_priv_frame_ptr() hardcodes 0x4c for the same instruction with R9. Encodings for the non-extended registers are unchanged. Problem showed up when trying to resurrect BPF_GCC CI (selftests built with BPF_GCC). This has gone unnoticed because clang reloads the address into R1 before each per-CPU access, so the destination is never an extended register. GCC keeps several per-CPU addresses live at once, and test_progs-bpf_gcc panics the kernel in global_percpu_data/init, where the address of a .percpu variable ends up in R5.
At a glance
- Exploitability
- Can be exploited locally on the machine with a low-privilege account. High risk of data exposure, data tampering, service disruption.
- Exploit odds
- 0.1% chance of exploitation in the next 30 days (EPSS).
- Fix
- No patch or advisory is linked yet. Look at mitigations or restrict exposure.
Timeline
- ReservedThe CVE id was reserved by its CNA
- PublishedDisclosed publicly on CVE.org and NVD
- Last updatedMost recent change to the record
Why it ranks here
- Exploited in the wild: no, CISA does not list it.
- Exploit odds: 0.1% in the next 30 days (EPSS).
- Severity: 7.8 HIGH (CVSS).
- Fix: none linked yet, which raises it.
Details
- Published
- Last modified
- Exploit probability
- 0.1% · EPSS, next 30 days
- Record status
- Received
Attack profile CVSS 3.1 · 7.8
- Attack vector
- Local
- Complexity
- Low
- Privileges needed
- Low
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
Raw vector
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Is it in your code?
Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.
Read https://cve-list.com/agent/cve/CVE-2026-89581.md and follow it. Check whether this project is affected by CVE-2026-89581. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.
