x86/fpu/signal: Change return code of restore_fpregs_from_user() to boolean

__fpu_sig_restore() only needs information about success or fail and no
real error code.

This cleans up the confusing conversion of the trap number, which is
returned by the *RSTOR() exception fixups, to an error code.

Suggested-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20210908132526.084109938@linutronix.de

arch/x86/kernel/fpu/signal.c

@@ -254,8 +254,8 @@ static int __restore_fpregs_from_user(void __user *buf, u64 xrestore,
  * Attempt to restore the FPU registers directly from user memory.
  * Pagefaults are handled and any errors returned are fatal.
  */
-static int restore_fpregs_from_user(void __user *buf, u64 xrestore,
-				    bool fx_only, unsigned int size)
+static bool restore_fpregs_from_user(void __user *buf, u64 xrestore,
+				     bool fx_only, unsigned int size)
 {
 	struct fpu *fpu = &current->thread.fpu;
 	int ret;
@@ -284,12 +284,11 @@ retry:
 
 		/* Try to handle #PF, but anything else is fatal. */
 		if (ret != X86_TRAP_PF)
-			return -EINVAL;
+			return false;
 
-		ret = fault_in_pages_readable(buf, size);
-		if (!ret)
+		if (!fault_in_pages_readable(buf, size))
 			goto retry;
-		return ret;
+		return false;
 	}
 
 	/*
@@ -306,7 +305,7 @@ retry:
 
 	fpregs_mark_activate();
 	fpregs_unlock();
-	return 0;
+	return true;
 }
 
 static bool __fpu_restore_sig(void __user *buf, void __user *buf_fx,
@@ -341,8 +340,8 @@ static bool __fpu_restore_sig(void __user *buf, void __user *buf_fx,
 		 * faults. If it does, fall back to the slow path below, going
 		 * through the kernel buffer with the enabled pagefault handler.
 		 */
-		return !restore_fpregs_from_user(buf_fx, user_xfeatures, fx_only,
-						 state_size);
+		return restore_fpregs_from_user(buf_fx, user_xfeatures, fx_only,
+						state_size);
 	}
 
 	/*