[PATCH v2 12/24] target/riscv: tb flag for shadow stack instructions

[Deepak Gupta]

Shadow stack instructions can be decoded as zimop / zcmop or shadow stack
instructions depending on whether shadow stack are enabled at current
privilege. This requires a TB flag so that correct TB generation and correct
TB lookup happens. `DisasContext` gets a field indicating whether bcfi is
enabled or not.

This patch also implements helper bcfi function which determines if bcfi
is enabled at current privilege or not. qemu-user also gets field
`ubcfien` indicating whether qemu user has shadow stack enabled or not.

Signed-off-by: Deepak Gupta <debug@rivosinc.com>
Co-developed-by: Jim Shu <jim.shu@sifive.com>
Co-developed-by: Andy Chiu <andy.chiu@sifive.com>
---
 target/riscv/cpu.c        |  2 ++
 target/riscv/cpu.h        |  4 ++++
 target/riscv/cpu_helper.c | 30 ++++++++++++++++++++++++++++++
 target/riscv/translate.c  |  4 ++++
 4 files changed, 40 insertions(+)

diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
index 6b50ae0e45..e1ff246c24 100644
--- a/target/riscv/cpu.c
+++ b/target/riscv/cpu.c
@@ -1029,6 +1029,8 @@ static void riscv_cpu_reset_hold(Object *obj, ResetType 
type)
 #ifdef CONFIG_USER_ONLY
     /* qemu-user for riscv, fcfi is off by default */
     env->ufcfien = false;
+    /* qemu-user for riscv, bcfi is off by default */
+    env->ubcfien = false;
 #endif
 
 #ifndef CONFIG_USER_ONLY
diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h
index 81283a1d76..0e0a9d2be1 100644
--- a/target/riscv/cpu.h
+++ b/target/riscv/cpu.h
@@ -231,6 +231,7 @@ struct CPUArchState {
 #ifdef CONFIG_USER_ONLY
     uint32_t elf_flags;
     bool ufcfien;
+    bool ubcfien;
 #endif
 
 #ifndef CONFIG_USER_ONLY
@@ -536,6 +537,7 @@ bool riscv_cpu_vector_enabled(CPURISCVState *env);
 void riscv_cpu_set_virt_enabled(CPURISCVState *env, bool enable);
 int riscv_env_mmu_index(CPURISCVState *env, bool ifetch);
 bool cpu_get_fcfien(CPURISCVState *env);
+bool cpu_get_bcfien(CPURISCVState *env);
 G_NORETURN void  riscv_cpu_do_unaligned_access(CPUState *cs, vaddr addr,
                                                MMUAccessType access_type,
                                                int mmu_idx, uintptr_t retaddr);
@@ -610,6 +612,8 @@ FIELD(TB_FLAGS, PRIV, 24, 2)
 FIELD(TB_FLAGS, AXL, 26, 2)
 /* zicfilp needs a TB flag to track indirect branches */
 FIELD(TB_FLAGS, FCFI_LP_EXPECTED, 28, 1)
+/* zicfiss needs a TB flag so that correct TB is located based on tb flags */
+FIELD(TB_FLAGS, BCFI_ENABLED, 29, 1)
 
 #ifdef TARGET_RISCV32
 #define riscv_cpu_mxl(env)  ((void)(env), MXL_RV32)
diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c
index 2cb1d45467..ce68f5af72 100644
--- a/target/riscv/cpu_helper.c
+++ b/target/riscv/cpu_helper.c
@@ -93,6 +93,32 @@ bool cpu_get_fcfien(CPURISCVState *env)
 #endif
 }
 
+bool cpu_get_bcfien(CPURISCVState *env)
+{
+#ifdef CONFIG_USER_ONLY
+    return env->ubcfien;
+#else
+    /* no cfi extension, return false */
+    if (!env_archcpu(env)->cfg.ext_zicfiss) {
+        return false;
+    }
+
+    switch (env->priv) {
+    case PRV_U:
+        return (env->senvcfg & SENVCFG_SSE) ? true : false;
+    case PRV_S:
+        if (env->virt_enabled) {
+            return (env->henvcfg & HENVCFG_SSE) ? true : false;
+        }
+        return (env->menvcfg & MENVCFG_SSE) ? true : false;
+    case PRV_M: /* M-mode shadow stack is always on if hart implements */
+        return true;
+    default:
+        g_assert_not_reached();
+    }
+#endif
+}
+
 void cpu_get_tb_cpu_state(CPURISCVState *env, vaddr *pc,
                           uint64_t *cs_base, uint32_t *pflags)
 {
@@ -146,6 +172,10 @@ void cpu_get_tb_cpu_state(CPURISCVState *env, vaddr *pc,
                            env->elp != NO_LP_EXPECTED);
     }
 
+    if (cpu_get_bcfien(env)) {
+        flags = FIELD_DP32(flags, TB_FLAGS, BCFI_ENABLED, 1);
+    }
+
 #ifdef CONFIG_USER_ONLY
     fs = EXT_STATUS_DIRTY;
     vs = EXT_STATUS_DIRTY;
diff --git a/target/riscv/translate.c b/target/riscv/translate.c
index c746d7df08..34c9bf093d 100644
--- a/target/riscv/translate.c
+++ b/target/riscv/translate.c
@@ -121,6 +121,8 @@ typedef struct DisasContext {
     /* zicfilp extension. cfi enabled or not. lp expected or not */
     bool fcfi_enabled;
     bool fcfi_lp_expected;
+    /* zicfiss extension, if shadow stack was enabled during TB gen */
+    bool bcfi_enabled;
 } DisasContext;
 
 static inline bool has_ext(DisasContext *ctx, uint32_t ext)
@@ -1243,6 +1245,8 @@ static void riscv_tr_init_disas_context(DisasContextBase 
*dcbase, CPUState *cs)
     ctx->pm_base_enabled = FIELD_EX32(tb_flags, TB_FLAGS, PM_BASE_ENABLED);
     ctx->ztso = cpu->cfg.ext_ztso;
     ctx->itrigger = FIELD_EX32(tb_flags, TB_FLAGS, ITRIGGER);
+    ctx->bcfi_enabled = cpu_get_bcfien(env) &&
+                        FIELD_EX32(tb_flags, TB_FLAGS, BCFI_ENABLED);
     ctx->fcfi_lp_expected = FIELD_EX32(tb_flags, TB_FLAGS, FCFI_LP_EXPECTED);
     ctx->fcfi_enabled = cpu_get_fcfien(env) && ctx->fcfi_lp_expected;
     ctx->zero = tcg_constant_tl(0);
-- 
2.44.0