CVE-2026-89581 bpf, x86: Fix per-CPU address resolution into an extended register

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 add1mod, which sets REX.B. REX.B...