linux-user/aarch64: Implement PR_TAGGED_ADDR_ENABLE

This is the prctl bit that controls whether syscalls accept tagged
addresses.  See Documentation/arm64/tagged-address-abi.rst in the
linux kernel.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20210212184902.1251044-21-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

linux-user/aarch64/target_syscall.h

@@ -30,4 +30,8 @@ struct target_pt_regs {
 # define TARGET_PR_PAC_APDBKEY   (1 << 3)
 # define TARGET_PR_PAC_APGAKEY   (1 << 4)
 
+#define TARGET_PR_SET_TAGGED_ADDR_CTRL 55
+#define TARGET_PR_GET_TAGGED_ADDR_CTRL 56
+# define TARGET_PR_TAGGED_ADDR_ENABLE  (1UL << 0)
+
 #endif /* AARCH64_TARGET_SYSCALL_H */

linux-user/syscall.c

@@ -10993,6 +10993,30 @@ static abi_long do_syscall1(void *cpu_env, int num, abi_long arg1,
                 }
             }
             return -TARGET_EINVAL;
+        case TARGET_PR_SET_TAGGED_ADDR_CTRL:
+            {
+                abi_ulong valid_mask = TARGET_PR_TAGGED_ADDR_ENABLE;
+                CPUARMState *env = cpu_env;
+
+                if ((arg2 & ~valid_mask) || arg3 || arg4 || arg5) {
+                    return -TARGET_EINVAL;
+                }
+                env->tagged_addr_enable = arg2 & TARGET_PR_TAGGED_ADDR_ENABLE;
+                return 0;
+            }
+        case TARGET_PR_GET_TAGGED_ADDR_CTRL:
+            {
+                abi_long ret = 0;
+                CPUARMState *env = cpu_env;
+
+                if (arg2 || arg3 || arg4 || arg5) {
+                    return -TARGET_EINVAL;
+                }
+                if (env->tagged_addr_enable) {
+                    ret |= TARGET_PR_TAGGED_ADDR_ENABLE;
+                }
+                return ret;
+            }
 #endif /* AARCH64 */
         case PR_GET_SECCOMP:
         case PR_SET_SECCOMP:

target/arm/cpu-param.h

@@ -20,6 +20,9 @@
 
 #ifdef CONFIG_USER_ONLY
 #define TARGET_PAGE_BITS 12
+# ifdef TARGET_AARCH64
+#  define TARGET_TAGGED_ADDRESSES
+# endif
 #else
 /*
  * ARMv7 and later CPUs have 4K pages minimum, but ARMv5 and v6

target/arm/cpu.h

@@ -721,6 +721,11 @@ typedef struct CPUARMState {
     const struct arm_boot_info *boot_info;
     /* Store GICv3CPUState to access from this struct */
     void *gicv3state;
+
+#ifdef TARGET_TAGGED_ADDRESSES
+    /* Linux syscall tagged address support */
+    bool tagged_addr_enable;
+#endif
 } CPUARMState;
 
 static inline void set_feature(CPUARMState *env, int feature)
@@ -3604,6 +3609,32 @@ static inline MemTxAttrs *typecheck_memtxattrs(MemTxAttrs *x)
  */
 #define PAGE_BTI  PAGE_TARGET_1
 
+#ifdef TARGET_TAGGED_ADDRESSES
+/**
+ * cpu_untagged_addr:
+ * @cs: CPU context
+ * @x: tagged address
+ *
+ * Remove any address tag from @x.  This is explicitly related to the
+ * linux syscall TIF_TAGGED_ADDR setting, not TBI in general.
+ *
+ * There should be a better place to put this, but we need this in
+ * include/exec/cpu_ldst.h, and not some place linux-user specific.
+ */
+static inline target_ulong cpu_untagged_addr(CPUState *cs, target_ulong x)
+{
+    ARMCPU *cpu = ARM_CPU(cs);
+    if (cpu->env.tagged_addr_enable) {
+        /*
+         * TBI is enabled for userspace but not kernelspace addresses.
+         * Only clear the tag if bit 55 is clear.
+         */
+        x &= sextract64(x, 0, 56);
+    }
+    return x;
+}
+#endif
+
 /*
  * Naming convention for isar_feature functions:
  * Functions which test 32-bit ID registers should have _aa32_ in