How to avoid accidental re-flash when secure boot enabled?
Posted: Mon Mar 09, 2020 2:48 pm
We have an application that uses the full secure boot procedure as documented in the manual - this all works great, and we rely on OTA updates after initial flash. Our flashing software calls esptool.py in the background with the following:
However, at production, several boards were put through the process twice which has now bricked them since the flash was encrypted the first time around and now can't load plain text images.
Is there any way to prevent this in future?? Are there any efuses that will prevent serial access to the ROM bootloader???
The efuses of a bricked unit are:
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esptool.py --port {0} -b 460800 --before default_reset --after hard_reset write_flash -z 0x1000 securebootloader.bin 0x10000 main.bin 0x8000 partition.binIs there any way to prevent this in future?? Are there any efuses that will prevent serial access to the ROM bootloader???
The efuses of a bricked unit are:
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EFUSE_NAME Description = [Meaningful Value] [Readable/Writeable] (Hex Value)
----------------------------------------------------------------------------------------
Security fuses:
FLASH_CRYPT_CNT Flash encryption mode counter = 1 R/W (0x1)
FLASH_CRYPT_CONFIG Flash encryption config (key tweak bits) = 15 R/W (0xf)
CONSOLE_DEBUG_DISABLE Disable ROM BASIC interpreter fallback = 1 R/W (0x1)
ABS_DONE_0 secure boot enabled for bootloader = 1 R/W (0x1)
ABS_DONE_1 secure boot abstract 1 locked = 0 R/W (0x0)
JTAG_DISABLE Disable JTAG = 1 R/W (0x1)
DISABLE_DL_ENCRYPT Disable flash encryption in UART bootloader = 1 R/W (0x1)
DISABLE_DL_DECRYPT Disable flash decryption in UART bootloader = 1 R/W (0x1)
DISABLE_DL_CACHE Disable flash cache in UART bootloader = 1 R/W (0x1)
BLK1 Flash encryption key
= ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? -/-
BLK2 Secure boot key
= ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? -/-
BLK3 Variable Block 3
= 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 R/W
Efuse fuses:
WR_DIS Efuse write disable mask = 384 R/W (0x180)
RD_DIS Efuse read disablemask = 3 R/W (0x3)
CODING_SCHEME Efuse variable block length scheme = 0 R/W (0x0)
KEY_STATUS Usage of efuse block 3 (reserved) = 0 R/W (0x0)
Config fuses:
XPD_SDIO_FORCE Ignore MTDI pin (GPIO12) for VDD_SDIO on reset = 0 R/W (0x0)
XPD_SDIO_REG If XPD_SDIO_FORCE, enable VDD_SDIO reg on reset = 0 R/W (0x0)
XPD_SDIO_TIEH If XPD_SDIO_FORCE & XPD_SDIO_REG, 1=3.3V 0=1.8V = 0 R/W (0x0)
CLK8M_FREQ 8MHz clock freq override = 53 R/W (0x35)
SPI_PAD_CONFIG_CLK Override SD_CLK pad (GPIO6/SPICLK) = 0 R/W (0x0)
SPI_PAD_CONFIG_Q Override SD_DATA_0 pad (GPIO7/SPIQ) = 0 R/W (0x0)
SPI_PAD_CONFIG_D Override SD_DATA_1 pad (GPIO8/SPID) = 0 R/W (0x0)
SPI_PAD_CONFIG_HD Override SD_DATA_2 pad (GPIO9/SPIHD) = 0 R/W (0x0)
SPI_PAD_CONFIG_CS0 Override SD_CMD pad (GPIO11/SPICS0) = 0 R/W (0x0)
DISABLE_SDIO_HOST Disable SDIO host = 0 R/W (0x0)
Identity fuses:
MAC Factory MAC Address
= 98:f4:ab:1c:66:50 (CRC 4e OK) R/W
CHIP_VER_REV1 Silicon Revision 1 = 1 R/W (0x1)
CHIP_VER_REV2 Silicon Revision 2 = 0 R/W (0x0)
CHIP_VERSION Reserved for future chip versions = 2 R/W (0x2)
CHIP_PACKAGE Chip package identifier = 1 R/W (0x1)
Calibration fuses:
BLK3_PART_RESERVE BLOCK3 partially served for ADC calibration data = 0 R/W (0x0)
ADC_VREF Voltage reference calibration = 1100 R/W (0x10)
Flash voltage (VDD_SDIO) determined by GPIO12 on reset (High for 1.8V, Low/NC for 3.3V).
- we will do a manual fuse check first.