target/arm: Set PAN bit as required on exception entry

The PAN bit is preserved, or set as per SCTLR_ELx.SPAN,
plus several other conditions listed in the ARM ARM.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 20200208125816.14954-15-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

target/arm/helper.c

@@ -8763,8 +8763,12 @@ static void take_aarch32_exception(CPUARMState *env, int new_mode,
                                    uint32_t mask, uint32_t offset,
                                    uint32_t newpc)
 {
+    int new_el;
+
     /* Change the CPU state so as to actually take the exception. */
     switch_mode(env, new_mode);
+    new_el = arm_current_el(env);
+
     /*
      * For exceptions taken to AArch32 we must clear the SS bit in both
      * PSTATE and in the old-state value we save to SPSR_<mode>, so zero it now.
@@ -8777,7 +8781,7 @@ static void take_aarch32_exception(CPUARMState *env, int new_mode,
     env->uncached_cpsr = (env->uncached_cpsr & ~CPSR_M) | new_mode;
     /* Set new mode endianness */
     env->uncached_cpsr &= ~CPSR_E;
-    if (env->cp15.sctlr_el[arm_current_el(env)] & SCTLR_EE) {
+    if (env->cp15.sctlr_el[new_el] & SCTLR_EE) {
         env->uncached_cpsr |= CPSR_E;
     }
     /* J and IL must always be cleared for exception entry */
@@ -8788,6 +8792,25 @@ static void take_aarch32_exception(CPUARMState *env, int new_mode,
         env->thumb = (env->cp15.sctlr_el[2] & SCTLR_TE) != 0;
         env->elr_el[2] = env->regs[15];
     } else {
+        /* CPSR.PAN is normally preserved preserved unless...  */
+        if (cpu_isar_feature(aa64_pan, env_archcpu(env))) {
+            switch (new_el) {
+            case 3:
+                if (!arm_is_secure_below_el3(env)) {
+                    /* ... the target is EL3, from non-secure state.  */
+                    env->uncached_cpsr &= ~CPSR_PAN;
+                    break;
+                }
+                /* ... the target is EL3, from secure state ... */
+                /* fall through */
+            case 1:
+                /* ... the target is EL1 and SCTLR.SPAN is 0.  */
+                if (!(env->cp15.sctlr_el[new_el] & SCTLR_SPAN)) {
+                    env->uncached_cpsr |= CPSR_PAN;
+                }
+                break;
+            }
+        }
         /*
          * this is a lie, as there was no c1_sys on V4T/V5, but who cares
          * and we should just guard the thumb mode on V4
@@ -9050,6 +9073,7 @@ static void arm_cpu_do_interrupt_aarch64(CPUState *cs)
     unsigned int new_el = env->exception.target_el;
     target_ulong addr = env->cp15.vbar_el[new_el];
     unsigned int new_mode = aarch64_pstate_mode(new_el, true);
+    unsigned int old_mode;
     unsigned int cur_el = arm_current_el(env);
 
     /*
@@ -9129,20 +9153,43 @@ static void arm_cpu_do_interrupt_aarch64(CPUState *cs)
     }
 
     if (is_a64(env)) {
-        env->banked_spsr[aarch64_banked_spsr_index(new_el)] = pstate_read(env);
+        old_mode = pstate_read(env);
         aarch64_save_sp(env, arm_current_el(env));
         env->elr_el[new_el] = env->pc;
     } else {
-        env->banked_spsr[aarch64_banked_spsr_index(new_el)] = cpsr_read(env);
+        old_mode = cpsr_read(env);
         env->elr_el[new_el] = env->regs[15];
 
         aarch64_sync_32_to_64(env);
 
         env->condexec_bits = 0;
     }
+    env->banked_spsr[aarch64_banked_spsr_index(new_el)] = old_mode;
+
     qemu_log_mask(CPU_LOG_INT, "...with ELR 0x%" PRIx64 "\n",
                   env->elr_el[new_el]);
 
+    if (cpu_isar_feature(aa64_pan, cpu)) {
+        /* The value of PSTATE.PAN is normally preserved, except when ... */
+        new_mode |= old_mode & PSTATE_PAN;
+        switch (new_el) {
+        case 2:
+            /* ... the target is EL2 with HCR_EL2.{E2H,TGE} == '11' ...  */
+            if ((arm_hcr_el2_eff(env) & (HCR_E2H | HCR_TGE))
+                != (HCR_E2H | HCR_TGE)) {
+                break;
+            }
+            /* fall through */
+        case 1:
+            /* ... the target is EL1 ... */
+            /* ... and SCTLR_ELx.SPAN == 0, then set to 1.  */
+            if ((env->cp15.sctlr_el[new_el] & SCTLR_SPAN) == 0) {
+                new_mode |= PSTATE_PAN;
+            }
+            break;
+        }
+    }
+
     pstate_write(env, PSTATE_DAIF | new_mode);
     env->aarch64 = 1;
     aarch64_restore_sp(env, new_el);