x86: copy_fpstate_to_sigframe(): have fpregs_soft_get() use kernel buffer

... then copy_to_user() the results
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

arch/x86/kernel/fpu/signal.c

@@ -170,14 +170,14 @@ int copy_fpstate_to_sigframe(void __user *buf, void __user *buf_fx, int size)
 	ia32_fxstate &= (IS_ENABLED(CONFIG_X86_32) ||
 			 IS_ENABLED(CONFIG_IA32_EMULATION));
 
+	if (!static_cpu_has(X86_FEATURE_FPU)) {
+		struct user_i387_ia32_struct fp;
+		fpregs_soft_get(current, NULL, 0, sizeof(fp), &fp, NULL);
+		return copy_to_user(buf, &fp, sizeof(fp)) ? -EFAULT : 0;
+	}
+
 	if (!access_ok(buf, size))
 		return -EACCES;
-
-	if (!static_cpu_has(X86_FEATURE_FPU))
-		return fpregs_soft_get(current, NULL, 0,
-			sizeof(struct user_i387_ia32_struct), NULL,
-			(struct _fpstate_32 __user *) buf) ? -1 : 1;
-
 retry:
 	/*
 	 * Load the FPU registers if they are not valid for the current task.