target/arm: Implement the HFGITR_EL2.ERET trap

Implement the HFGITR_EL2.ERET fine-grained trap.  This traps
execution from AArch64 EL1 of ERET, ERETAA and ERETAB.  The trap is
reported with a syndrome value of 0x1a.

The trap must take precedence over a possible pointer-authentication
trap for ERETAA and ERETAB.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Tested-by: Fuad Tabba <tabba@google.com>
Message-id: 20230130182459.3309057-21-peter.maydell@linaro.org
Message-id: 20230127175507.2895013-21-peter.maydell@linaro.org

target/arm/cpu.h

@@ -3245,6 +3245,7 @@ FIELD(TBFLAG_A64, PSTATE_ZA, 23, 1)
 FIELD(TBFLAG_A64, SVL, 24, 4)
 /* Indicates that SME Streaming mode is active, and SMCR_ELx.FA64 is not. */
 FIELD(TBFLAG_A64, SME_TRAP_NONSTREAMING, 28, 1)
+FIELD(TBFLAG_A64, FGT_ERET, 29, 1)
 
 /*
  * Helpers for using the above.

target/arm/helper.c

@@ -12065,6 +12065,9 @@ static CPUARMTBFlags rebuild_hflags_a64(CPUARMState *env, int el, int fp_el,
 
     if (arm_fgt_active(env, el)) {
         DP_TBFLAG_ANY(flags, FGT_ACTIVE, 1);
+        if (FIELD_EX64(env->cp15.fgt_exec[FGTREG_HFGITR], HFGITR_EL2, ERET)) {
+            DP_TBFLAG_A64(flags, FGT_ERET, 1);
+        }
     }
 
     if (cpu_isar_feature(aa64_mte, env_archcpu(env))) {

target/arm/syndrome.h

@@ -48,6 +48,7 @@ enum arm_exception_class {
     EC_AA64_SMC               = 0x17,
     EC_SYSTEMREGISTERTRAP     = 0x18,
     EC_SVEACCESSTRAP          = 0x19,
+    EC_ERETTRAP               = 0x1a,
     EC_SMETRAP                = 0x1d,
     EC_INSNABORT              = 0x20,
     EC_INSNABORT_SAME_EL      = 0x21,
@@ -215,6 +216,15 @@ static inline uint32_t syn_sve_access_trap(void)
     return EC_SVEACCESSTRAP << ARM_EL_EC_SHIFT;
 }
 
+/*
+ * eret_op is bits [1:0] of the ERET instruction, so:
+ * 0 for ERET, 2 for ERETAA, 3 for ERETAB.
+ */
+static inline uint32_t syn_erettrap(int eret_op)
+{
+    return (EC_ERETTRAP << ARM_EL_EC_SHIFT) | ARM_EL_IL | eret_op;
+}
+
 static inline uint32_t syn_smetrap(SMEExceptionType etype, bool is_16bit)
 {
     return (EC_SMETRAP << ARM_EL_EC_SHIFT)

target/arm/translate-a64.c

@@ -2385,6 +2385,10 @@ static void disas_uncond_b_reg(DisasContext *s, uint32_t insn)
             if (op4 != 0) {
                 goto do_unallocated;
             }
+            if (s->fgt_eret) {
+                gen_exception_insn_el(s, 0, EXCP_UDEF, syn_erettrap(op3), 2);
+                return;
+            }
             dst = tcg_temp_new_i64();
             tcg_gen_ld_i64(dst, cpu_env,
                            offsetof(CPUARMState, elr_el[s->current_el]));
@@ -2398,6 +2402,11 @@ static void disas_uncond_b_reg(DisasContext *s, uint32_t insn)
             if (rn != 0x1f || op4 != 0x1f) {
                 goto do_unallocated;
             }
+            /* The FGT trap takes precedence over an auth trap. */
+            if (s->fgt_eret) {
+                gen_exception_insn_el(s, 0, EXCP_UDEF, syn_erettrap(op3), 2);
+                return;
+            }
             dst = tcg_temp_new_i64();
             tcg_gen_ld_i64(dst, cpu_env,
                            offsetof(CPUARMState, elr_el[s->current_el]));
@@ -14742,6 +14751,7 @@ static void aarch64_tr_init_disas_context(DisasContextBase *dcbase,
     dc->align_mem = EX_TBFLAG_ANY(tb_flags, ALIGN_MEM);
     dc->pstate_il = EX_TBFLAG_ANY(tb_flags, PSTATE__IL);
     dc->fgt_active = EX_TBFLAG_ANY(tb_flags, FGT_ACTIVE);
+    dc->fgt_eret = EX_TBFLAG_A64(tb_flags, FGT_ERET);
     dc->sve_excp_el = EX_TBFLAG_A64(tb_flags, SVEEXC_EL);
     dc->sme_excp_el = EX_TBFLAG_A64(tb_flags, SMEEXC_EL);
     dc->vl = (EX_TBFLAG_A64(tb_flags, VL) + 1) * 16;

target/arm/translate.h

@@ -132,6 +132,8 @@ typedef struct DisasContext {
     bool mve_no_pred;
     /* True if fine-grained traps are active */
     bool fgt_active;
+    /* True if fine-grained trap on ERET is enabled */
+    bool fgt_eret;
     /*
      * >= 0, a copy of PSTATE.BTYPE, which will be 0 without v8.5-BTI.
      *  < 0, set by the current instruction.