target/riscv: Validate the mode in write_vstvec

Base on the riscv-privileged spec, vstvec substitutes for the usual stvec.
Therefore, the encoding of the MODE should also be restricted to 0 and 1.

Signed-off-by: Jiayi Li <lijiayi@eswincomputing.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: LIU Zhiwei <zhiwei_liu@linux.alibaba.com>
Message-ID: <20240701022553.1982-1-lijiayi@eswincomputing.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

diff --git a/target/riscv/csr.c b/target/riscv/csr.c
index 432c59dc66bef54615912f6eb4ee4112fc3f24f7..f9229d92ab3ab1eab565a1fec4798b5ed1285dd4 100644 (file)
--- a/target/riscv/csr.c
+++ b/target/riscv/csr.c
@@ -3791,7 +3791,12 @@ static RISCVException read_vstvec(CPURISCVState *env, int csrno,
 static RISCVException write_vstvec(CPURISCVState *env, int csrno,
                                    target_ulong val)
 {
-    env->vstvec = val;
+    /* bits [1:0] encode mode; 0 = direct, 1 = vectored, 2 >= reserved */
+    if ((val & 3) < 2) {
+        env->vstvec = val;
+    } else {
+        qemu_log_mask(LOG_UNIMP, "CSR_VSTVEC: reserved mode not supported\n");
+    }
     return RISCV_EXCP_NONE;
 }