1# HP Sure Start 2 3According to the [HP Sure Start Technical Whitepaper], HP Sure Start is a chipset 4and processor independent firmware intrusion detection and automatic repair system. 5It is implemented in HP notebooks since 2013, and desktops since 2015. 6 7This document talks about some mechanism of HP Sure Start on some machines, and 8the method to bypass it. 9 10## Laptops with SMSC MEC1322 embedded controller 11 12Haswell EliteBook, ZBook and ProBook 600 series use SMSC MEC1322 embedded controller. 13The EC firmware implements HP Sure Start. 14 15A Haswell EliteBook has two flash chips. According to the strings in the EC firmware, 16the 16MiB flash chip that stores the BIOS firmware is called the *system flash*, and 17the 2MiB flash chip that stores part of the system flash content is called the 18*private flash*. A Haswell ProBook 600 series laptop also uses MEC1322 and has similar 19EC firmware, but the HP Sure Start functions are not enabled. 20 21The private flash is connected to the EC, and is not accessible by the OS. 22It contains the following: 23 24- HP Sure Start policy header (starting with the string "POLI") 25- A copy of the Intel Flash Descriptor 26- A copy of the GbE firmware 27- Machine Unique Data (MUD) 28- Hashes of the IFD, GbE firmware and MUD, the hash algorithm is unknown 29- A copy of the bootblock, UEFI PEI stage, and microcode 30 31If the IFD of the system flash does not match the hash in the private flash, for example, 32modifying the IFD with ``ifdtool -u`` or ``me_cleaner -S``, the EC will recover the IFD. 33 34If the content of the private flash is lost, the EC firmware will still copy the IFD, 35bootblock and PEI to the private flash. However, the IFD is not protected after that. 36 37HP Sure Start also verifies bootblock, PEI, and microcode without using the private flash. 38EC firmware reads them from an absolute address of the system flash chip, which is 39hardcoded in the EC firmware. It looks like this verification is done with a digital 40signature. If the PEI volume is modified, EC firmware will recover it using the copy 41in the private flash. If the private flash has no valid copies of the PEI volume, and 42the PEI volume is modified, the machine will refuse to boot with the CapsLock LED blinking. 43 44## Bypassing HP Sure Start 45 46First search the mainboard for the flash chips. If there are two flash chips, 47the smaller one may be the private flash. 48 49For Intel boards, try to modify the IFD with ``ifdtool -u``, power on and shut down 50the machine, then read the flash again. If the IFD is not modified, it is likely to 51be recovered from the private flash. Find the private flash and erase it, then the IFD 52can be modified. 53 54To bypass the bootblock and PEI verification, we can modify the IFD to make the 55BIOS region not overlap with the protected region. Since the EC firmware is usually 56located at the high address of the flash chip (and in the protected region), 57we can leave it untouched, and do not need to extract the EC firmware to put it in 58the coreboot image. 59 60[HP Sure Start Technical Whitepaper]: http://h10032.www1.hp.com/ctg/Manual/c05163901 61