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secure boot v2: esp32: Prevent read disabling additional efuses

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Also reduce the number of eFuse write cycles during first boot when
Secure Boot and/or Flash Encryption are enabled.
This commit is contained in:
Angus Gratton
2020-03-20 13:55:15 +11:00
committed by Angus Gratton
parent f96d28172b
commit cf8dd62fc4
4 changed files with 73 additions and 25 deletions
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12
components/bootloader/Kconfig.projbuild
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@@ -640,6 +640,18 @@ menu "Security features"
image to this length. It is generally not recommended to set this option, unless you have a legacy
partitioning scheme which doesn't support 64KB aligned partition lengths.
config SECURE_BOOT_V2_ALLOW_EFUSE_RD_DIS
bool "Allow additional read protecting of efuses"
depends on SECURE_BOOT_INSECURE && SECURE_BOOT_V2_ENABLED
help
If not set (default, recommended), on first boot the bootloader will burn the WR_DIS_RD_DIS
efuse when Secure Boot is enabled. This prevents any more efuses from being read protected.
If this option is set, it will remain possible to write the EFUSE_RD_DIS efuse field after Secure
Boot is enabled. This may allow an attacker to read-protect the BLK2 efuse holding the public
key digest, causing an immediate denial of service and possibly allowing an additional fault
injection attack to bypass the signature protection.
config SECURE_FLASH_UART_BOOTLOADER_ALLOW_ENC
bool "Leave UART bootloader encryption enabled"
depends on SECURE_FLASH_ENCRYPTION_MODE_DEVELOPMENT