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@@ -10302,6 +10303,73 @@ The difference between the two timestamps is the cost of everything wolfBoot doe
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Both caches are enabled by `hal_init()`, which matters because verifying an image means hashing megabytes resident in DDR. The ARMv7-M default memory map marks `0x80000000-0x9FFFFFFF` as Normal write-through, so no MPU region is needed and M7 stores to the shared window still reach DDR; the HAL nevertheless cleans the affected lines explicitly so that behaviour is not left depending on an inherited attribute.
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## NXP i.MX95 Cortex-A55 (BL33)
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wolfBoot replaces U-Boot proper on the i.MX95's Cortex-A55 cluster: it is the third image in AHAB container 2 (after BL31 and OP-TEE), entered by BL31 at `0x90200000` in NS-EL2, where it verifies a Linux FIT (kernel + DTB + initramfs) with ML-DSA-87 and boots it at EL2. NXP also documents an OEM PQC SRK hybrid (ML-DSA) AHAB flow, so the container half of the chain can be post-quantum as well.
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Which component authenticates the containers depends on which slot wolfBoot occupies, and the two cases are not the same:
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-**wolfBoot as BL33 only** (this section). U-Boot SPL is still in container 0 and still calls the ELE to authenticate container 2 before BL31 runs, so the chain is ROM -> ELE -> SPL -> BL31 -> wolfBoot -> Linux once SRK fuses are programmed.
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-**wolfBoot as stage 1 as well** (next section). SPL is gone, so wolfBoot performs that ELE call itself. `IMX95_AHAB_AUTH` is what does it, and it is on by default; the chain becomes ROM -> ELE -> wolfBoot stage 1 -> BL31 -> wolfBoot BL33 -> Linux.
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In both cases the ROM and the ELE authenticate container 0 before any A55 code runs, so whichever image sits in the SPL slot is itself verified.
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Validated on a Toradex SMARC iMX95 with `TARGET=imx95_a55` (`config/examples/imx95-a55.config`): full boot to Linux userspace with the FIT on the carrier SD (uSDHC2, the uSDHC driver in `hal/imx95_a55.c` - i.MX uSDHC, not SDHCI-compatible).
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Notes:
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- The FIT DTB gets `/chosen` bootargs, initrd properties and a `/memory` node from `hal_dts_fixup()`; deployment DTBs commonly ship without `/memory` (the bootloader is expected to add it) and the kernel hangs silently without one.
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- The EL2 exit is a fused asm routine (flush, DAIF mask, TLB invalidate, jump) that touches no memory after the D-cache goes off; set/way cleaning does not reach the A55 cluster's DSU system cache, so payload ranges are also cleaned by VA.
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- Use plain `earlycon` (DTB-derived); an explicit `earlycon=lpuart32,mmio32,<addr>` uses the wrong register layout on i.MX and silences all console output.
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- uSDHC2's clock, pinmux and card power are owned by the M33 System Manager, and its pad registers data-abort on direct access from BL33. `IMX95_SCMI_COLD_INIT=1` brings them up over SCMI (the SCMI client in `hal/imx95_a55.c`), which is what lets wolfBoot boot from SD on a cold power-on rather than only after a stage that already initialized the controller.
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-`IMX95_INIT_M7=1` powers the Cortex-M7 mix and scrubs its TCM for ECC, matching what U-Boot's board init does, for boards that launch an M7 image from Linux later.
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### Stage 1: replacing U-Boot SPL
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The boot device holds a set of AHAB containers. The first one is what the boot ROM reads: it carries the ELE firmware, the M33 System Manager, the OEI that trains DDR, and one A55 image loaded into OCRAM at `0x20480000`. That last image is U-Boot SPL, and its whole job is to find the next container and load BL31, OP-TEE and BL33 out of it. wolfBoot can take that slot instead:
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```
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cp config/examples/imx95-a55.config .config
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make # BL33, loaded into DRAM by BL31
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make stage1 DISK_EMMC=1 # stage1/loader_stage1.bin, the SPL slot
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```
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DDR is up before stage 1 runs, because the OEI did it, so stage 1 only needs the boot device and the container walk. Nothing records where the next container starts: it is derived by taking the end of the first container - the furthest of its header, its images and its signature block - and rounding up to 1 KiB. `hal/imx95_ahab.c` is that walk, and `hal/imx95_a55_stage1.c` is the rest: the watchdog, GPIO and SMMU state a warm reset out of Linux leaves behind, the SCMI calls for the console clock and the A55 performance level, and the ELE call that starts its random generator.
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Two things differ from the BL33 build. The console is programmed rather than inherited, since nothing has configured LPUART1 yet. And on eMMC the containers live in a boot partition, not the user area: `imx95_emmc_boot_partition()` reads back the same `PARTITION_CONFIG` field that told the ROM which one to load from, and reads follow it.
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#### What stage 1 authenticates
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Taking SPL's slot means taking over the step SPL performed. The boot ROM and the ELE authenticate container 0, so stage 1 is verified code, but the container it goes on to load BL31, OP-TEE and BL33 out of is a separate one that nothing has checked yet. `IMX95_AHAB_AUTH=1` (the default) makes stage 1 ask the ELE to check it, the same three calls U-Boot's SPL makes:
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1. The container's header, image table and signature block are staged into DDR at `0x90000000` - NXP's own `IMG_CONTAINER_BASE` for this SoC - because the ELE reads the address it is given over its own master port and requires DDR. Every value stage 1 then acts on comes from those staged bytes; the medium is not consulted for the table again.
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2.`ELE_OEM_CNTN_AUTH_REQ` authenticates the header.
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3. Each image is loaded to its destination and then checked in place with `ELE_VERIFY_IMAGE_REQ`, one at a time so a failure names the image. `ELE_RELEASE_CONTAINER_REQ` follows, before the jump.
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Any failure stops the boot. `IMX95_AHAB_AUTH=0` builds without those calls, for bring-up on a part whose containers are not signed. `IMX95_STAGE1_PASSTHROUGH` and `IMX95_STAGE1_ALLOW_SELF_OVERLAP` each carry on past a container the enclave refused, so both require `IMX95_AHAB_AUTH=0`; setting either while authentication is on fails the build.
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Separately, and regardless of that flag, stage 1 bounds every destination *before* writing any of them. An image is streamed straight from the boot device into the address the container names, so a check made afterwards would come too late to matter: by then the bytes have landed. Destinations must lie inside DDR, must not overlap the staging window, this loader, the M7 carveout, the ELE shared-memory region or the VPU boot area, must not overlap each other once rounded up to the block size, and image 0 must be an A55 executable whose entry point lies inside its own bytes.
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Two limits are worth stating plainly:
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-**On an open part AHAB reports success without enforcing a signature.** That is why an unsigned container boots at all. What authentication buys there is an ELE-checked hash of each image against a table nobody signed - integrity, not authenticity. Build with `IMX95_AHAB_LIFECYCLE=1` to have stage 1 print the lifecycle, so the difference is visible rather than implied; it is off by default because nothing else on this platform reads the fuse shadow block from the slot SPL occupies. Enforcement begins when the SRK hash is fused; see the i.MX8QuadMax AHAB section above for what that costs and why it is irreversible.
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-**Authenticating the container does not prevent rollback.** The offset of the next container is derived by walking container 0, which stage 1 reads off the medium and nothing re-authenticates, so a different but validly signed older container set would authenticate happily. That needs `sw_version`/`fuse_version` policy or the AHAB monotonic counter, neither of which is implemented here.
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#### Stage 1 build options
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Stage 1 is built by `make -C stage1` and takes its own options, separately from the BL33 build. Pass them on the command line.
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| Option | Default | Effect |
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|---|---|---|
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|`IMX95_AHAB_AUTH`|`1`| Ask the ELE to authenticate the container set stage 1 loads BL31, OP-TEE and BL33 from, as described above. Setting it to `0` builds without those calls, for bring-up on a part whose containers are not signed. |
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|`IMX95_AHAB_LIFECYCLE`|`0`| Read and print the part's lifecycle from the fuse shadow block. Off by default: U-Boot reads that block only from U-Boot proper and only under `CONFIG_AHAB_BOOT`, so whether it answers the A55 this early is untested per part, and a diagnostic must not be able to cost a boot. |
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|`IMX95_STAGE1_PASSTHROUGH`| unset | Bring-up only. Enter BL31 even when the container load failed, for a board where some other loader has already staged the whole set and stage 1 only needs to be invisible when it cannot help. Requires `IMX95_AHAB_AUTH=0`, and is refused at compile time otherwise, because returning an error is then indistinguishable from the jump. |
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|`IMX95_STAGE1_ALLOW_SELF_OVERLAP`| unset | Bring-up only. Skip an image whose destination lands on the running loader instead of refusing the boot, which a stage 1 linked into DRAM needs in order to skip its own entry. Requires `IMX95_AHAB_AUTH=0`, and is refused at compile time otherwise. |
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|`IMX95_LOG_RING`|`0`| Mirror the console into a DDR ring that survives the handoff, so stage 1's output can be read back from Linux with `memtool con`. Stage 1 starts the ring and BL33 appends to it, so one address holds both. |
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|`IMX95_LOG_RING_BASE`|`0x80F20000`| Where that ring lives. Change it only to move the ring out of the way of something else; stage 1 and BL33 must agree on it. |
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|`IMX95_EMMC_PROBE`|`0`| One-shot diagnostic that walks the eMMC boot partitions and reports the AHAB containers it finds, from an image booting off SD. |
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The two bring-up options exist to get a new board talking; neither belongs in a shipped configuration, and the build refuses to combine either with authentication rather than letting a boot continue past a refusal.
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## TI C2000 C28x (LAUNCHXL-F28P55X)
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wolfBoot runs on the Texas Instruments C2000 C28x DSP (TMS320F28P550SJ, 150 MHz) as a secure execute-in-place (XIP) bootloader. The C28x is word-addressed with `CHAR_BIT == 16` (no 8-bit type -- each octet occupies one 16-bit cell), built with the TI `cl2000` toolchain against wolfSSL's wide-byte (`CHAR_BIT != 8`) support.
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