linux-user: Restrict usage of sa_restorer

Reading and writing to an sa_restorer member that isn't supposed to
exist corrupts user memory.  Introduce TARGET_ARCH_HAS_SA_RESTORER,
similar to the kernel's __ARCH_HAS_SA_RESTORER.

Reported-by: Helge Deller <deller@gmx.de>
Signed-off-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Riku Voipio <riku.voipio@linaro.org>

linux-user/signal.c

@@ -777,7 +777,7 @@ int do_sigaction(int sig, const struct target_sigaction *act,
     if (oact) {
         __put_user(k->_sa_handler, &oact->_sa_handler);
         __put_user(k->sa_flags, &oact->sa_flags);
-#if !defined(TARGET_MIPS)
+#ifdef TARGET_ARCH_HAS_SA_RESTORER
         __put_user(k->sa_restorer, &oact->sa_restorer);
 #endif
         /* Not swapped.  */
@@ -787,7 +787,7 @@ int do_sigaction(int sig, const struct target_sigaction *act,
         /* FIXME: This is not threadsafe.  */
         __get_user(k->_sa_handler, &act->_sa_handler);
         __get_user(k->sa_flags, &act->sa_flags);
-#if !defined(TARGET_MIPS)
+#ifdef TARGET_ARCH_HAS_SA_RESTORER
         __get_user(k->sa_restorer, &act->sa_restorer);
 #endif
         /* To be swapped in target_to_host_sigset.  */

linux-user/syscall_defs.h

@@ -445,6 +445,7 @@ int do_sigaction(int sig, const struct target_sigaction *act,
 #define TARGET_SA_RESTART      2u
 #define TARGET_SA_NODEFER      0x20u
 #define TARGET_SA_RESETHAND    4u
+#define TARGET_ARCH_HAS_SA_RESTORER 1
 #elif defined(TARGET_MIPS)
 #define TARGET_SA_NOCLDSTOP	0x00000001
 #define TARGET_SA_NOCLDWAIT	0x00010000
@@ -483,6 +484,10 @@ int do_sigaction(int sig, const struct target_sigaction *act,
 #define TARGET_SA_RESTORER	0x04000000
 #endif
 
+#ifdef TARGET_SA_RESTORER
+#define TARGET_ARCH_HAS_SA_RESTORER 1
+#endif
+
 #if defined(TARGET_ALPHA)
 
 #define TARGET_SIGHUP            1
@@ -718,19 +723,27 @@ struct target_sigaction {
 	abi_ulong	_sa_handler;
 #endif
 	target_sigset_t	sa_mask;
+#ifdef TARGET_ARCH_HAS_SA_RESTORER
+        /* ??? This is always present, but ignored unless O32.  */
+        abi_ulong sa_restorer;
+#endif
 };
 #else
 struct target_old_sigaction {
         abi_ulong _sa_handler;
         abi_ulong sa_mask;
         abi_ulong sa_flags;
+#ifdef TARGET_ARCH_HAS_SA_RESTORER
         abi_ulong sa_restorer;
+#endif
 };
 
 struct target_sigaction {
         abi_ulong _sa_handler;
         abi_ulong sa_flags;
+#ifdef TARGET_ARCH_HAS_SA_RESTORER
         abi_ulong sa_restorer;
+#endif
         target_sigset_t sa_mask;
 };
 #endif