Secure boot problem

[vlad2891]

Hello guys,

Lately I'we been having trouble getting secure boot working on the ESP32 device ( been using adafruit devboards). So what I do basically is :
1. have a private key /secure_boot_signing_key.pem
2. extract public key by doing

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python espsecure.py extract_public_key --keyfile <project_path>/secure_boot_signing_key.pem <project_path>/signature_verification_key.bin

and I get signature_verification_key.bin
3.

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 make bootloader

then gives me

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python esptool.py --chip esp32 --port COM5 --baud 115200 --before default_reset --after no_reset write_flash -z --flash_mode dio --flash_freq 40m --flash_size detect 0x1000 <project_path>/build/bootloader/bootloader.bin

.
4. After I run the previous command I do a

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make flash

5. after rebooting I get the following

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rst:0x10 (RTCWDT_RTC_RESET),boot:0x13 (SPI_FAST_FLASH_BOOT)
configsip: 0, SPIWP:0x00
clk_drv:0x00,q_drv:0x00,d_drv:0x00,cs0_drv:0x00,hd_drv:0x00,wp_drv:0x00
mode:DIO, clock div:2
load:0x3fff0008,len:8
load:0x3fff0010,len:3844
load:0x40078000,len:12912
ho 0 tail 12 room 4
load:0x40080000,len:252
entry 0x40080034
E (47) secure_boot: bootloader image appears invalid! error 258
E (47) boot: Bootloader digest generation failed (258). SECURE BOOT IS NOT ENABLED.
I (1204) cpu_start: Pro cpu up.
I (1205) cpu_start: Single core mode
I (1206) heap_alloc_caps: Initializing. RAM available for dynamic allocation:
I (1219) heap_alloc_caps: At 3FFAE2A0 len 00001D60 (7 KiB): DRAM
I (1239) heap_alloc_caps: At 3FFBA600 len 00025A00 (150 KiB): DRAM
I (1260) heap_alloc_caps: At 3FFE0440 len 00003BC0 (14 KiB): D/IRAM
I (1282) heap_alloc_caps: At 3FFE4350 len 0001BCB0 (111 KiB): D/IRAM
I (1303) heap_alloc_caps: At 4009B6C0 len 00004940 (18 KiB): IRAM
I (1324) cpu_start: Pro cpu start user code
I (1385) cpu_start: Starting scheduler on PRO CPU.
I (1390) [MAIN]: Initialization started
I (1390) [MAIN]: Software version: 0.1
I (1393) [MAIN]: IDF version: v2.0-rc1-302-g57486a1

The problem being here

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E (47) secure_boot: bootloader image appears invalid! error 258
E (47) boot: Bootloader digest generation failed (258). SECURE BOOT IS NOT ENABLED.

You can check the sdkconfig.

I'we been using this as a guide and at this point I don't get what I'm missing.

If you need any further info please let me know.

Any help will be appreciated. Thank you,
Vlad

[vlad2891]

Hello guys,

After taking a peak through the esp-idf itself, I found that the error is first detected here in esp_image_format.c:111

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if (src_addr % SPI_FLASH_MMU_PAGE_SIZE != 0) {
        /* Image must start on a 64KB boundary

           (This is not a technical limitation, only the flash mapped regions need to be 64KB aligned.  But the most
           consistent way to do this is to have all the offsets internal to the image correctly 64KB aligned, and then
           start the image on a 64KB boundary also.)
         */
        return ESP_ERR_INVALID_ARG;
    }

Can anyone give me a hint on what this means and what am I doing wrong?

Thank you,
Vlad

[vlad2891]

Hello guys,

So, digging around more I found this scenario:
1. On boot, if secure boot enabled, secured boot enabled is called (bootloader_start.c#L357)

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err = esp_secure_boot_permanently_enable();

2. this leads to secure_boot.c file that calls image verify (secure_boot.c#L114)

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 err = esp_image_basic_verify(0x1000, true, &image_len);

here the src_image is hardcoded to 0x1000

3. in the esp_image_format.c we reach the above check (esp_image_format.c#L111)

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if (src_addr % SPI_FLASH_MMU_PAGE_SIZE != 0) { ...

4. the value for SPI_FLASH_MMU_PAGE_SIZE comes from (esp_spi_flash.h#L34) where is defined as 0x10000.

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#define SPI_FLASH_MMU_PAGE_SIZE 0x10000 /**< Flash cache MMU mapping page size */

Here is the tricky part, from 2,3 and 4, replacing the values we get

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if ( 0x1000 %  0x10000 != 0) { ...

This will always return true( 0x1000 % 0x10000 = 0x1000 != 0), thus leaving the secure boot disabled.

Is there a reason this is disabled or is it a bug? Let me know what you guys think.

Regards,
Vlad

[ESP_igrr]

Thanks for reporting this, seems to be a bug.

[ESP_Angus]

Sorry for the delay in replying.

This has been fixed in esp-idf master branch as of commit 32fc0a62b9e20dbf6499f8ebf4a5026fe05e28ce, and will be in the forthcoming v2.1 release.

[smeedy]

Hi Angus,

Nice! We've been waiting for this to be fixed. Thanks for the effort.

regards,
Martijn