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authorRouven Czerwinski <r.czerwinski@pengutronix.de>2019-09-23 10:19:02 +0200
committerSascha Hauer <s.hauer@pengutronix.de>2019-09-25 11:40:31 +0200
commite2f42fbbe7eded87b8784a574af615fb8dc34f85 (patch)
tree4caae736b058bbfc0e1a1c2a60002f0f0a051038 /Documentation
parent1b78b514419823b38d0540d836a49a25e53d575e (diff)
downloadbarebox-e2f42fbbe7eded87b8784a574af615fb8dc34f85.tar.gz
Doc: i.MX: Document image structure for i.MX
Document the image and load structure for i.MX6 and i.MX8MQ. Signed-off-by: Rouven Czerwinski <r.czerwinski@pengutronix.de> Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
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@@ -142,6 +142,79 @@ It must be included in the board's flash header:
Analogous to HABv4 options and a template exist for HABv3.
+Secure Boot on i.MX6
+~~~~~~~~~~~~~~~~~~~~
+
+For most boards, the secure boot process on i.MX6 consist of the following image
+constellation::
+
+ 0x0 +---------------------------------+
+ | Barebox Header |
+ 0x400 +---------------------------------+ -
+ | i.MX IVT Header | |
+ | Boot Data +--+ |
+ | CSF Pointer +--|-+ | Signed Area
+ +---------------------------------+ | | |
+ | Device Configuration Data (DCD) | | | |
+ 0x1000 +---------------------------------+ | | |
+ | Barebox Prebootloader (PBL) |<-+ | |
+ +---------------------------------+ | |
+ | Piggydata (Main Barebox Binary) | | |
+ +---------------------------------+ | -
+ | Command Sequence File (CSF) |<---+
+ +---------------------------------+
+
+Here the Command Sequence File signs the complete Header, PBL and piggy data
+file. This ensures that the whole barebox binary is authenticated. This is
+possible since the DDR RAM is configured using the DCD and the whole DDR memory
+area can be used to load data onto the device for authentication.
+The boot ROM loads the CSF area and barebox into memory and uses the CSF to
+verify the complete barebox binary.
+
+Boards which do require a boot via SRAM, need changes akin to the implementation
+for i.MX8MQ described in the next chapter.
+
+Secure Boot on i.MX8MQ
+~~~~~~~~~~~~~~~~~~~~~~
+
+For i.MX8MQ the image has the following design::
+
+ 0x0 +---------------------------------+
+ | Barebox Header |
+ +---------------------------------+
+ | i.MX IVT Header |
+ | HDMI Firmware (Signed by NXP) |
+ +---------------------------------+ -
+ | i.MX IVT Header | |
+ | Boot Data +--+ |
+ | CSF Pointer +--|-+ |
+ +---------------------------------+ | | | Signed Area
+ | Device Configuration Data (DCD) | | | |
+ +---------------------------------+ | | |
+ | Barebox Prebootloader (PBL) |<-+ | |
+ | Piggydata Hash (SHA256) +----|-+ |
+ +---------------------------------+ | | -
+ | Command Sequence File (CSF) |<---+ |
+ +---------------------------------+ | -
+ | Piggydata (Main Barebox Binary) |<-----+ | Hashed Area
+ +---------------------------------+ -
+
+In contrast to i.MX6, for the i.MX8MQ the piggydata can not be signed together
+with the PBL binary. The DDR memory is initialized during the start of the PBL,
+previous to this no access to the DDR memory is possible. Since the Tightly
+Coupled Memory used for early startup on i.MX8MQ has only 256Kib, the whole
+barebox can't be loaded and verified at once, since the complete barebox with
+firmware has a size of ~500Kib.
+
+The bootrom loads the HDMI firmware unconditionally, since it is signed by NXP.
+Afterwards the Prebootloader (PBL) is loaded into SRAM and the bootrom proceeds
+to verify the PBL according to the Command Sequence File (CSF). The verified
+PBL initializes the ARM Trusted Firmware (TF-A) and DDR RAM. It subsequently
+loads the piggydata from the boot media and calculates the sha256sum of the
+piggydata. This is compared to the sha256sum built into the PBL during compile
+time, the PBL will only continue to boot if the sha256sum matches the builtin
+sha256sum.
+
Using GPT on i.MX
^^^^^^^^^^^^^^^^^