target/arm: Implement NSACR gating of floating point

The NSACR register allows secure code to configure the FPU
to be inaccessible to non-secure code. If the NSACR.CP10
bit is set then:
 * NS accesses to the FPU trap as UNDEF (ie to NS EL1 or EL2)
 * CPACR.{CP10,CP11} behave as if RAZ/WI
 * HCPTR.{TCP11,TCP10} behave as if RAO/WI

Note that we do not implement the NSACR.NSASEDIS bit which
gates only access to Advanced SIMD, in the same way that
we don't implement the equivalent CPACR.ASEDIS and HCPTR.TASE.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 20190510110357.18825-1-peter.maydell@linaro.org

target/arm/helper.c

@@ -930,9 +930,36 @@ static void cpacr_write(CPUARMState *env, const ARMCPRegInfo *ri,
         }
         value &= mask;
     }
+
+    /*
+     * For A-profile AArch32 EL3 (but not M-profile secure mode), if NSACR.CP10
+     * is 0 then CPACR.{CP11,CP10} ignore writes and read as 0b00.
+     */
+    if (arm_feature(env, ARM_FEATURE_EL3) && !arm_el_is_aa64(env, 3) &&
+        !arm_is_secure(env) && !extract32(env->cp15.nsacr, 10, 1)) {
+        value &= ~(0xf << 20);
+        value |= env->cp15.cpacr_el1 & (0xf << 20);
+    }
+
     env->cp15.cpacr_el1 = value;
 }
 
+static uint64_t cpacr_read(CPUARMState *env, const ARMCPRegInfo *ri)
+{
+    /*
+     * For A-profile AArch32 EL3 (but not M-profile secure mode), if NSACR.CP10
+     * is 0 then CPACR.{CP11,CP10} ignore writes and read as 0b00.
+     */
+    uint64_t value = env->cp15.cpacr_el1;
+
+    if (arm_feature(env, ARM_FEATURE_EL3) && !arm_el_is_aa64(env, 3) &&
+        !arm_is_secure(env) && !extract32(env->cp15.nsacr, 10, 1)) {
+        value &= ~(0xf << 20);
+    }
+    return value;
+}
+
+
 static void cpacr_reset(CPUARMState *env, const ARMCPRegInfo *ri)
 {
     /* Call cpacr_write() so that we reset with the correct RAO bits set
@@ -998,7 +1025,7 @@ static const ARMCPRegInfo v6_cp_reginfo[] = {
     { .name = "CPACR", .state = ARM_CP_STATE_BOTH, .opc0 = 3,
       .crn = 1, .crm = 0, .opc1 = 0, .opc2 = 2, .accessfn = cpacr_access,
       .access = PL1_RW, .fieldoffset = offsetof(CPUARMState, cp15.cpacr_el1),
-      .resetfn = cpacr_reset, .writefn = cpacr_write },
+      .resetfn = cpacr_reset, .writefn = cpacr_write, .readfn = cpacr_read },
     REGINFO_SENTINEL
 };
 
@@ -4683,6 +4710,36 @@ uint64_t arm_hcr_el2_eff(CPUARMState *env)
     return ret;
 }
 
+static void cptr_el2_write(CPUARMState *env, const ARMCPRegInfo *ri,
+                           uint64_t value)
+{
+    /*
+     * For A-profile AArch32 EL3, if NSACR.CP10
+     * is 0 then HCPTR.{TCP11,TCP10} ignore writes and read as 1.
+     */
+    if (arm_feature(env, ARM_FEATURE_EL3) && !arm_el_is_aa64(env, 3) &&
+        !arm_is_secure(env) && !extract32(env->cp15.nsacr, 10, 1)) {
+        value &= ~(0x3 << 10);
+        value |= env->cp15.cptr_el[2] & (0x3 << 10);
+    }
+    env->cp15.cptr_el[2] = value;
+}
+
+static uint64_t cptr_el2_read(CPUARMState *env, const ARMCPRegInfo *ri)
+{
+    /*
+     * For A-profile AArch32 EL3, if NSACR.CP10
+     * is 0 then HCPTR.{TCP11,TCP10} ignore writes and read as 1.
+     */
+    uint64_t value = env->cp15.cptr_el[2];
+
+    if (arm_feature(env, ARM_FEATURE_EL3) && !arm_el_is_aa64(env, 3) &&
+        !arm_is_secure(env) && !extract32(env->cp15.nsacr, 10, 1)) {
+        value |= 0x3 << 10;
+    }
+    return value;
+}
+
 static const ARMCPRegInfo el2_cp_reginfo[] = {
     { .name = "HCR_EL2", .state = ARM_CP_STATE_AA64,
       .type = ARM_CP_IO,
@@ -4730,7 +4787,8 @@ static const ARMCPRegInfo el2_cp_reginfo[] = {
     { .name = "CPTR_EL2", .state = ARM_CP_STATE_BOTH,
       .opc0 = 3, .opc1 = 4, .crn = 1, .crm = 1, .opc2 = 2,
       .access = PL2_RW, .accessfn = cptr_access, .resetvalue = 0,
-      .fieldoffset = offsetof(CPUARMState, cp15.cptr_el[2]) },
+      .fieldoffset = offsetof(CPUARMState, cp15.cptr_el[2]),
+      .readfn = cptr_el2_read, .writefn = cptr_el2_write },
     { .name = "MAIR_EL2", .state = ARM_CP_STATE_BOTH,
       .opc0 = 3, .opc1 = 4, .crn = 10, .crm = 2, .opc2 = 0,
       .access = PL2_RW, .fieldoffset = offsetof(CPUARMState, cp15.mair_el[2]),
@@ -13587,6 +13645,19 @@ int fp_exception_el(CPUARMState *env, int cur_el)
         break;
     }
 
+    /*
+     * The NSACR allows A-profile AArch32 EL3 and M-profile secure mode
+     * to control non-secure access to the FPU. It doesn't have any
+     * effect if EL3 is AArch64 or if EL3 doesn't exist at all.
+     */
+    if ((arm_feature(env, ARM_FEATURE_EL3) && !arm_el_is_aa64(env, 3) &&
+         cur_el <= 2 && !arm_is_secure_below_el3(env))) {
+        if (!extract32(env->cp15.nsacr, 10, 1)) {
+            /* FP insns act as UNDEF */
+            return cur_el == 2 ? 2 : 1;
+        }
+    }
+
     /* For the CPTR registers we don't need to guard with an ARM_FEATURE
      * check because zero bits in the registers mean "don't trap".
      */