powerpc/ptrace: Use copy_{from, to}_user() rather than open-coding

In PPC_PTRACE_GETHWDBGINFO and PPC_PTRACE_SETHWDEBUG we do an
access_ok() check and then __copy_{from,to}_user().

Instead we should just use copy_{from,to}_user() which does all that
for us and is less error prone.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Reviewed-by: Samuel Mendoza-Jonas <sam@mendozajonas.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/kernel/ptrace.c

@@ -3082,27 +3082,19 @@ long arch_ptrace(struct task_struct *child, long request,
 #endif /* CONFIG_HAVE_HW_BREAKPOINT */
 #endif /* CONFIG_PPC_ADV_DEBUG_REGS */
 
-		if (!access_ok(VERIFY_WRITE, datavp,
-			       sizeof(struct ppc_debug_info)))
+		if (copy_to_user(datavp, &dbginfo,
+				 sizeof(struct ppc_debug_info)))
 			return -EFAULT;
-		ret = __copy_to_user(datavp, &dbginfo,
-				     sizeof(struct ppc_debug_info)) ?
-		      -EFAULT : 0;
-		break;
+		return 0;
 	}
 
 	case PPC_PTRACE_SETHWDEBUG: {
 		struct ppc_hw_breakpoint bp_info;
 
-		if (!access_ok(VERIFY_READ, datavp,
-			       sizeof(struct ppc_hw_breakpoint)))
+		if (copy_from_user(&bp_info, datavp,
+				   sizeof(struct ppc_hw_breakpoint)))
 			return -EFAULT;
-		ret = __copy_from_user(&bp_info, datavp,
-				       sizeof(struct ppc_hw_breakpoint)) ?
-		      -EFAULT : 0;
-		if (!ret)
-			ret = ppc_set_hwdebug(child, &bp_info);
-		break;
+		return ppc_set_hwdebug(child, &bp_info);
 	}
 
 	case PPC_PTRACE_DELHWDEBUG: {