github.com/transparency-dev/armored-witness-boot@v0.1.0/console.go (about)

     1  // Copyright 2022 The Armored Witness Boot authors. All Rights Reserved.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  //go:build !console
    16  // +build !console
    17  
    18  package main
    19  
    20  import (
    21  	"io"
    22  	"log"
    23  	_ "unsafe"
    24  
    25  	"github.com/usbarmory/tamago/soc/nxp/imx6ul"
    26  )
    27  
    28  // This bootloader does not log any sensitive information to the serial
    29  // console, however it is desirable to silence any potential stack trace or
    30  // runtime errors to avoid unwanted information leaks.
    31  //
    32  // The TamaGo board support for the USB armory Mk II enables the serial console
    33  // (UART2) at runtime initialization, which therefore invokes imx6.UART2.Init()
    34  // before init().
    35  //
    36  // To this end the runtime printk function, responsible for all console logging
    37  // operations (i.e. stdout/stderr), is overridden with a NOP. Secondarily UART2
    38  // is disabled at the first opportunity (init()).
    39  
    40  func init() {
    41  	// disable console
    42  	imx6ul.UART2.Disable()
    43  	// silence logging
    44  	log.SetOutput(io.Discard)
    45  }
    46  
    47  //go:linkname printk runtime.printk
    48  func printk(c byte) {
    49  	// ensure that any serial output is supressed before UART2 disabling
    50  }