Add extension point for checking CSR access.csr_ext

2 files changed, 17 insertions, 0 deletions

diff --git a/model/riscv_ext_regs.sail b/model/riscv_ext_regs.sail
index 9ff83b3..b03ecd5 100644
--- a/model/riscv_ext_regs.sail
+++ b/model/riscv_ext_regs.sail
@@ -12,3 +12,18 @@ to omnipotent instead of null).
  */
 val ext_rvfi_init : unit -> unit effect {wreg}
 function ext_rvfi_init () = ()
+
+
+/*!
+THIS(csrno, priv, isWrite) allows an extension to block access to csrno,
+at Privilege level priv. It should return true if the access is allowed.
+*/
+val ext_check_CSR : (bits(12), Privilege, bool) -> bool
+function ext_check_CSR (csrno, p, isWrite) = true
+
+/*!
+THIS is called if ext_check_CSR returns false. It should
+cause an appropriate RISCV exception.
+ */
+val ext_check_CSR_fail : unit->unit
+function ext_check_CSR_fail () = ()
diff --git a/model/riscv_insts_zicsr.sail b/model/riscv_insts_zicsr.sail
index dd8a4a0..056f537 100644
--- a/model/riscv_insts_zicsr.sail
+++ b/model/riscv_insts_zicsr.sail
@@ -179,6 +179,8 @@ function clause execute CSR(csr, rs1, rd, is_imm, op) = {
   };
   if ~ (check_CSR(csr, cur_privilege, isWrite))
   then { handle_illegal(); RETIRE_FAIL }
+  else if ~ (ext_check_CSR(csr, cur_privilege, isWrite))
+  then { ext_check_CSR_fail(); RETIRE_FAIL }
   else {
     let csr_val = readCSR(csr); /* could have side-effects, so technically shouldn't perform for CSRW[I] with rd == 0 */
     if isWrite then {