13 posts tagged linux, newest first.
You cannot put a filesystem's hash inside that filesystem. Two U-Boot messages that were lies — “press any key to stop autoboot” when no key worked, and quotes vanishing from the kernel command line. Four attempts, three instructive failures, and a hardware SHA engine I did not know I was using.
The negative test that proves the chain is real: flip a single bit in a 52 MB root filesystem, get `data block 0 is corrupted`, and watch the board refuse. Why you cannot sabotage your own firmware the two obvious ways.
The hash of a filesystem cannot live inside it, so the kernel had to move somewhere signed. Then the two-command test: hand the bootloader rubbish and watch the kernel ignore it entirely. What that cost, and where the chain now ends.
You cannot sign a zImage. Why the signature goes on the FIT configuration rather than the kernel, the escape hatch that turns the whole thing into theatre, why the negative test needed two tampered images and not one, and the three ways the test lied to me.
TF-A verifying the next stage against a certificate chain inside the FIP — software, on blank fuses, refusing for real. Flipping one bit produced EAUTH on BL33 and a clean halt. Plus the honest limits of what that proves.
Secure boot on this chip comes down to 32 bytes in one-time-programmable memory, and a bit you can never un-blow. I started the project with a rule forbidding its own last step — and three of the four links in the chain turn out to enforce for real on completely blank silicon.
The repeatable runbook, and the reason flashing a pre-made image left me with a 512 MB data partition instead of 28 gigabytes.
The board flashed perfectly and never reached Linux. A Kconfig choice split upstream had silently retargeted my bootloader at the wrong DRAM.
NXP's uuu dies at 8% on an Apple Silicon Mac. The board's own U-Boot has ums and fastboot, and those use bulk USB, which works fine.
Extending the chain from the bootloader to the kernel. The first signed Image failed with HAB_INV_ASSERTION — because I read NXP's own diagram literally and stopped the signed range one IVT short. How I decoded the event by hand and found the off-by-32-bytes.
My imx-boot build failed LPDDR4 training and the gateway stopped booting before U-Boot. The cause was one Kconfig symbol. Recovering it took days, because uuu's SDP mode does not work on Apple Silicon and the board has two identical-looking micro-USB ports.
Before touching a bootloader, take a backup you can actually restore from. On an i.MX8M Plus that means four separate things, two of which a dd of the main device silently misses — and one that is not block data at all.
What you need to follow this series: a CompuLab IOT-DIN-IMX8PLUS industrial gateway on an NXP i.MX8M Plus, a serial cable, and a spare unit you are willing to break. Plus the commands to confirm which variant you have, because it decides what you build.