Support for zisslpcfi in opensbi

zisslpcfi [1] extension extends risc-v architecture to mitigate against control-flow integrity attacks (ROP/JOP/COP).

zisslpcfi uses bits (b23-b26) in (m/s/vs) status CSR for enabling cfi in U mode and record cfi state. One such state is expected landing pad (ELP). If forward cfi is enabled, indirect call/jmp updates hart's ELP state (1bit) to true. ELP state is cleared only by a landing pad instruction else trap is delivered with ELP state recorded in sstatus CSR.

This two patch series adds following changes to opensbi
- Adds support in opensbi to detect zisslpcfi
- trap redirection updates ELP state accordingly

Qemu implementation for zisslpcfi can be checked out on github [2] Strawman linux kernel enabling (still very early) can be checked out on github [3]

[1] - https://github.com/riscv/riscv-cfi
[2] - https://github.com/deepak0414/qemu/tree/gh_Zisslpcfi-0.1
[3] - https://github.com/deepak0414/linux-riscv-cfi/tree/Zisslpcfi-0.1_v6.1-rc2

Deepak Gupta (2):
include: adding support for Zisslpcfi encodings
lib: sbi: Zisslpcfi detection and elp cfi state reflect back in status

 include/sbi/riscv_encoding.h | 10 ++++++++++
 include/sbi/sbi_hart.h       |  2 ++
 lib/sbi/sbi_hart.c           | 23 +++++++++++++++++++++++
 lib/sbi/sbi_trap.c           | 16 ++++++++++++++++
 4 files changed, 51 insertions(+)

2.25.1