target/arm: Use TCF0 and TFSRE0 for unprivileged tag checks

Section D6.7 of the ARM ARM states:

For the purpose of determining Tag Check Fault handling, unprivileged
load and store instructions are treated as if executed at EL0 when
executed at either:
- EL1, when the Effective value of PSTATE.UAO is 0.
- EL2, when both the Effective value of HCR_EL2.{E2H, TGE} is {1, 1}
  and the Effective value of PSTATE.UAO is 0.

ARM has confirmed a defect in the pseudocode function
AArch64.TagCheckFault that makes it inconsistent with the above
wording. The remedy is to adjust references to PSTATE.EL in that
function to instead refer to AArch64.AccessUsesEL(acctype), so
that unprivileged instructions use SCTLR_EL1.TCF0 and TFSRE0_EL1.
The exception type for synchronous tag check faults remains unchanged.

This patch implements the described change by partially reverting
commits 50244cc and cc97b00.

Signed-off-by: Peter Collingbourne <pcc@google.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20210219201820.2672077-1-pcc@google.com
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

target/arm/helper.c

@@ -13170,7 +13170,7 @@ static uint32_t rebuild_hflags_a64(CPUARMState *env, int el, int fp_el,
         if (FIELD_EX32(flags, TBFLAG_A64, UNPRIV)
             && tbid
             && !(env->pstate & PSTATE_TCO)
-            && (sctlr & SCTLR_TCF)
+            && (sctlr & SCTLR_TCF0)
             && allocation_tag_access_enabled(env, 0, sctlr)) {
             flags = FIELD_DP32(flags, TBFLAG_A64, MTE0_ACTIVE, 1);
         }

target/arm/mte_helper.c

@@ -550,10 +550,14 @@ static void mte_check_fail(CPUARMState *env, uint32_t desc,
     reg_el = regime_el(env, arm_mmu_idx);
     sctlr = env->cp15.sctlr_el[reg_el];
 
-    el = arm_current_el(env);
-    if (el == 0) {
+    switch (arm_mmu_idx) {
+    case ARMMMUIdx_E10_0:
+    case ARMMMUIdx_E20_0:
+        el = 0;
         tcf = extract64(sctlr, 38, 2);
-    } else {
+        break;
+    default:
+        el = reg_el;
         tcf = extract64(sctlr, 40, 2);
     }
 
@@ -570,7 +574,8 @@ static void mte_check_fail(CPUARMState *env, uint32_t desc,
         env->exception.vaddress = dirty_ptr;
 
         is_write = FIELD_EX32(desc, MTEDESC, WRITE);
-        syn = syn_data_abort_no_iss(el != 0, 0, 0, 0, 0, is_write, 0x11);
+        syn = syn_data_abort_no_iss(arm_current_el(env) != 0, 0, 0, 0, 0,
+                                    is_write, 0x11);
         raise_exception(env, EXCP_DATA_ABORT, syn, exception_target_el(env));
         /* noreturn, but fall through to the assert anyway */