RISC-V In Linux 7.0 Brings User-Space CFI & Optimized strlen Assembly

The RISC-V architecture updates have been merged for Linux 7.0 with a few items to note.

First up, RISC-V is finally ready to support control-flow integrity “CFI” for user-space applications with Linux 7.0. Complementing control flow integrity with shadow stack handling that has been available on Intel and AMD processors, RISC-V with Linux 7.0 is supporting similar CFI handling. This security feature is for fending off ROP attacks manipulating the control flow of the user-space software to gain control. RISC-V uses the “zicfilp” and “zicfiss” instructions to enforce that all indirect calls land on a landing pad “lpad” instruction or will otherwise raise a software check exception. There are also RISC-V instructions introduced for helping ensure the return flow of software.

RISC-V in Linux 7.0 has also optimized its string length “strlen” implementation in hand-coded Assembly. The loop body drops from 4 instructions to 3 instructions and eliminates an unconditional jump with the new tuned Assembly. There are further Assembly optimizations that may land in a future Linux kernel release.

RISC-V in Linux 7.0 also improves its ptrace behavior around vector registers, enables the ISO-8859-1 code page as built-in for EFI volume mounting, and various code clean-ups.

More details on these now merged RISC-V port changes for Linux 7.0 via this pull.