From 19baeb5120565e1b1be0e6c4c4bbfbb67f4e66db Mon Sep 17 00:00:00 2001
From: Peter Maydell <peter.maydell@linaro.org>
Date: Thu, 8 Mar 2018 09:42:01 -0500
Subject: [PATCH] target/arm: Implement v8M MSPLIM and PSPLIM registers

The v8M architecture includes hardware support for enforcing
stack pointer limits. We don't implement this behaviour yet,
but provide the MSPLIM and PSPLIM stack pointer limit registers
as reads-as-written, so that when we do implement the checks
in future this won't break guest migration.

Backports commit 57bb31568114023f67680d6fe478ceb13c51aa7d from qemu
---
 qemu/target/arm/cpu.h    |  2 ++
 qemu/target/arm/helper.c | 46 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 48 insertions(+)

diff --git a/qemu/target/arm/cpu.h b/qemu/target/arm/cpu.h
index 3855e785..1c0b89e5 100644
--- a/qemu/target/arm/cpu.h
+++ b/qemu/target/arm/cpu.h
@@ -502,6 +502,8 @@ typedef struct CPUARMState {
         uint32_t secure; /* Is CPU in Secure state? (not guest visible) */
         uint32_t csselr[M_REG_NUM_BANKS];
         uint32_t scr[M_REG_NUM_BANKS];
+        uint32_t msplim[M_REG_NUM_BANKS];
+        uint32_t psplim[M_REG_NUM_BANKS];
     } v7m;
 
     /* Information associated with an exception about to be taken:
diff --git a/qemu/target/arm/helper.c b/qemu/target/arm/helper.c
index a592de6c..fdd94c1d 100644
--- a/qemu/target/arm/helper.c
+++ b/qemu/target/arm/helper.c
@@ -9576,6 +9576,16 @@ uint32_t HELPER(v7m_mrs)(CPUARMState *env, uint32_t reg)
                 return 0;
             }
             return env->v7m.other_ss_psp;
+        case 0x8a: /* MSPLIM_NS */
+            if (!env->v7m.secure) {
+                return 0;
+            }
+            return env->v7m.msplim[M_REG_NS];
+        case 0x8b: /* PSPLIM_NS */
+            if (!env->v7m.secure) {
+                return 0;
+            }
+            return env->v7m.psplim[M_REG_NS];
         case 0x90: /* PRIMASK_NS */
             if (!env->v7m.secure) {
                 return 0;
@@ -9617,6 +9627,16 @@ uint32_t HELPER(v7m_mrs)(CPUARMState *env, uint32_t reg)
         return v7m_using_psp(env) ? env->v7m.other_sp : env->regs[13];
     case 9: /* PSP */
         return v7m_using_psp(env) ? env->regs[13] : env->v7m.other_sp;
+    case 10: /* MSPLIM */
+        if (!arm_feature(env, ARM_FEATURE_V8)) {
+            goto bad_reg;
+        }
+        return env->v7m.msplim[env->v7m.secure];
+    case 11: /* PSPLIM */
+        if (!arm_feature(env, ARM_FEATURE_V8)) {
+            goto bad_reg;
+        }
+        return env->v7m.psplim[env->v7m.secure];
     case 16: /* PRIMASK */
         return env->v7m.primask[env->v7m.secure];
     case 17: /* BASEPRI */
@@ -9625,6 +9645,7 @@ uint32_t HELPER(v7m_mrs)(CPUARMState *env, uint32_t reg)
     case 19: /* FAULTMASK */
         return env->v7m.faultmask[env->v7m.secure];
     default:
+    bad_reg:
         /* ??? For debugging only.  */
         qemu_log_mask(LOG_GUEST_ERROR, "Attempt to read unknown special"
                                        " register %d\n", reg);
@@ -9663,6 +9684,18 @@ void HELPER(v7m_msr)(CPUARMState *env, uint32_t maskreg, uint32_t val)
             }
             env->v7m.other_ss_psp = val;
             return;
+        case 0x8a: /* MSPLIM_NS */
+            if (!env->v7m.secure) {
+                return;
+            }
+            env->v7m.msplim[M_REG_NS] = val & ~7;
+            return;
+        case 0x8b: /* PSPLIM_NS */
+            if (!env->v7m.secure) {
+                return;
+            }
+            env->v7m.psplim[M_REG_NS] = val & ~7;
+            return;
         case 0x90: /* PRIMASK_NS */
             if (!env->v7m.secure) {
                 return;
@@ -9749,6 +9782,18 @@ void HELPER(v7m_msr)(CPUARMState *env, uint32_t maskreg, uint32_t val)
             env->v7m.other_sp = val;
         }
         break;
+    case 10: /* MSPLIM */
+        if (!arm_feature(env, ARM_FEATURE_V8)) {
+            goto bad_reg;
+        }
+        env->v7m.msplim[env->v7m.secure] = val & ~7;
+        break;
+    case 11: /* PSPLIM */
+        if (!arm_feature(env, ARM_FEATURE_V8)) {
+            goto bad_reg;
+        }
+        env->v7m.psplim[env->v7m.secure] = val & ~7;
+        break;
     case 16: /* PRIMASK */
         env->v7m.primask[env->v7m.secure] = val & 1;
         break;
@@ -9781,6 +9826,7 @@ void HELPER(v7m_msr)(CPUARMState *env, uint32_t maskreg, uint32_t val)
         env->v7m.control[env->v7m.secure] |= val & R_V7M_CONTROL_NPRIV_MASK;
         break;
     default:
+    bad_reg:
         qemu_log_mask(LOG_GUEST_ERROR, "Attempt to write unknown special"
                                        " register %d\n", reg);
         return;