[PATCH] target/riscv: Validate the mode in write_vstvec

[Jiayi Li]

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 <liji...@eswincomputing.com>
---
 target/riscv/csr.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/target/riscv/csr.c b/target/riscv/csr.c
index 432c59dc66..f9229d92ab 100644
--- 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;
 }
 
-- 
2.25.1