powerpc/signal32: Add and use unsafe_put_sigset_t()

put_sigset_t() calls copy_to_user() for copying two words.

This is terribly inefficient for copying two words.

By switching to unsafe_put_user(), we end up with something as
simple as:

 3cc:   81 3d 00 00     lwz     r9,0(r29)
 3d0:   91 26 00 b4     stw     r9,180(r6)
 3d4:   81 3d 00 04     lwz     r9,4(r29)
 3d8:   91 26 00 b8     stw     r9,184(r6)
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/06def97e87ac1c4ae8e3197e0982e1fab7b3c8ae.1597770847.git.christophe.leroy@csgroup.eu

arch/powerpc/kernel/signal_32.c

@@ -87,6 +87,8 @@ static inline int put_sigset_t(compat_sigset_t __user *uset, sigset_t *set)
 	return put_compat_sigset(uset, set, sizeof(*uset));
 }
 
+#define unsafe_put_sigset_t	unsafe_put_compat_sigset
+
 static inline int get_sigset_t(sigset_t *set,
 			       const compat_sigset_t __user *uset)
 {
@@ -141,6 +143,13 @@ static inline int put_sigset_t(sigset_t __user *uset, sigset_t *set)
 	return copy_to_user(uset, set, sizeof(*uset));
 }
 
+#define unsafe_put_sigset_t(uset, set, label) do {			\
+	sigset_t __user *__us = uset	;				\
+	const sigset_t *__s = set;					\
+									\
+	unsafe_copy_to_user(__us, __s, sizeof(*__us), label);		\
+} while (0)
+
 static inline int get_sigset_t(sigset_t *set, const sigset_t __user *uset)
 {
 	return copy_from_user(set, uset, sizeof(*uset));
@@ -780,10 +789,10 @@ int handle_rt_signal32(struct ksignal *ksig, sigset_t *oldset,
 				failed);
 		unsafe_put_user(PPC_INST_SC, &mctx->mc_pad[1], failed);
 	}
+	unsafe_put_sigset_t(&frame->uc.uc_sigmask, oldset, failed);
+
 	user_write_access_end();
 
-	if (put_sigset_t(&frame->uc.uc_sigmask, oldset))
-		goto badframe;
 	if (copy_siginfo_to_user(&frame->info, &ksig->info))
 		goto badframe;