SiVal ROM_EXT

Lockdowns

The following lockdowns are provided by the SiVal ROM_EXT.

AST

Access to the AST configuration registers is disabled by the ePMP configuration. The manufacturer may also configure the ROM to lockdown AST in the ROM stage by configuring the AST initialization sequence in OTP.

ePMP

The ePMP will allow access to the FLASH, to the MMIO region and to SRAM.

An example of how the SiVal ROM_EXT will configure the ePMP:

 0: 40130000 NAPOT L--- sz=00001000     ; OTP MMIO lockout.
 1: 40480000 NAPOT L--- sz=00000400     ; AST MMIO lockout.
 2: 20010400 ----- ---- sz=00000000     ; OWNER code start.
 3: 20013cac   TOR -X-R sz=000038ac     ; OWNER code end.
 4: 00000000 ----- ---- sz=00000000     ; OWNER data (if using remap window, else unused).
 5: 00000000 ----- ---- sz=00000000
 6: 00000000 ----- ---- sz=00000000
 7: 00000000 ----- ---- sz=00000000
 8: 00000000 ----- ---- sz=00000000
 9: 00000000 ----- ---- sz=00000000
10: 20000400 ----- ---- sz=00000000     ; ROM_EXT code start.
11: 20005bc8   TOR -X-R sz=000057c8     ; ROM_EXT code end.
12: 20000000 NAPOT L--R sz=00100000     ; FLASH data (1 MB).
13: 00010000 NAPOT LXWR sz=00001000     ; RvDM region (not PROD, RMA/DEV only).
14: 40000000 NAPOT L-WR sz=10000000     ; MMIO region.
15: 10000000 NAPOT L-WR sz=00020000     ; RAM region.
mseccfg = 00000002                      ; RLB=0, MMWP=1, MML=0.

In this configuration, the owner stage can re-arrange ePMP entries 2-11 as needed. Applications that require machine/user mode isolation can set the MML bit after arranging the ePMP to the preferred configuration.

NOTE: if the ROM_EXT stage is booted in the virtual slot, then ePMP entries 9/10/11 will be used to map the virtual window’s code/data segments. Since these entries are unlocked and since the ROM_EXT is no longer requred after owner code boots, these entries can be reclaimed for owner use.

OTP

  • The OTP creator partition memory window is locked and is unreadable.
  • The OTP owner partition memory window is readable.
  • The OTP direct access interface is not available due to the ePMP lockout of the OTP register region.

SRAM

SRAM execution is forbidden to force all PROD SiVal configurations to enforce signature verification of programs loaded into the flash owner partitions.

Both the ePMP and SRAM controller will forbid execution from SRAM. The SRAM controller configuration is locked by the ROM_EXT.

FLASH

The FLASH info pages designed for silicon_creator use are locked as no-access.

Page IDBankPage
kFlashCtrlInfoPageFactoryId00
kFlashCtrlInfoPageCreatorSecret01
kFlashCtrlInfoPageOwnerSecret02
kFlashCtrlInfoPageWaferAuthSecret03
kFlashCtrlInfoPageAttestationKeySeeds04
kFlashCtrlInfoPageBootData010
kFlashCtrlInfoPageBootData111
kFlashCtrlInfoPageOwnerSlot012
kFlashCtrlInfoPageOwnerSlot113

The canonical info flash reference used by the ROM and the ROM_EXT is available in the sw/device/silicon_creator/lib/drivers/flash_ctrl.h module.

Key Manager

The key manager will be moved to the final state so that no creator or intermediate stages may be accessed by owner code.

The end state of the key manager is kKeymgrStateOwnerKey for this configuration.