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diff --git a/util/e6400-flash-unlock/README.md b/util/e6400-flash-unlock/README.md deleted file mode 100644 index bc9dd9f9..00000000 --- a/util/e6400-flash-unlock/README.md +++ /dev/null @@ -1,102 +0,0 @@ -# Dell Laptop Internal Flashing - -This utility allows you to use flashrom's internal programmer to program the -entire BIOS flash chip from software while still running the original Dell -BIOS, which normally restricts software writes to the flash chip. It seems like -this works on any Dell laptop that has an EC similar to the SMSC MEC5035 on the -E6400, which mainly seem to be the Latitude and Precision lines starting from -around 2008 (E6400 era). - -## TL;DR -Run `make` to compile the utility, and then run `sudo ./e6400_flash_unlock` and -follow the directions it outputs. - -## Confirmed supported devices -- Latitude E6400 -- Latitude E6410 -- Latitude E4310 -- Latitude E6430 -- Precision M6800 - -It is likely that any other Latitude/Precision laptops from the same era as -devices specifically mentioned in the above list will work as Dell seems to use -the same ECs in one generation. - -## Detailed device specific behavior -- On GM45 era laptops, the expected behavior is that you will run the utility - for the first time, which will tell the EC to set the descriptor override on - the next boot. Then you will need to shut down the system, after which the - system will automatically boot up. You should then re-run the utility to - disable SMM, after which you can run flashrom. Finally, you should run the - utility a third time to reenable SMM so that shutdown works properly - afterwards. -- On 1st Generation Intel Core systems such as the E6410 and newer, run the - utility and shutdown in the same way as the E6400. However, it seems like the - EC no longer automatically boots the system. In this case you should manually - power it on. It also seems that the firmware does not set the BIOS Lock bit - when the descriptor override is set, making the 2nd run after the reboot - technically unnecessary. There is no harm in rerunning it though, as the - utility can detect when the flash is unlocked and perform the correct steps - as necessary. - -## How it works -There are several ways the firmware can protect itself from being overwritten. -One way is the Intel Flash Descriptor (IFD) permissions. On Intel systems, the -flash image is divided into several regions such as the IFD itself, Gigabit -Ethernet (GBE) non-volative memory, Management Engine (ME) firmware, Platform -Data (PD), and the BIOS. The IFD contains a section which specifies the -read/write permissions for each SPI controller (such as the host system) and -each region of the flash, which are enforced by the chipset. - -On the Latitude E6400, the host has read-only access to the IFD, no access to -the ME region, and read-write access to the PD, GBE, and BIOS regions. In order -for flashrom to write to the entire flash internally, the host needs full -permissions to all of these regions. Since the IFD is read only, we cannot -change these permissions unless we directly access the chip using an external -programmer, which defeats the purpose of internal flashing. - -However, Intel chipsets have a pin strap that allows the flash descriptor -permissions to be overridden depending on the value of the pin at power on, -granting RW permissions to all regions. On the ICH9M chipset on the E6400, this -pin is HDA\_DOCK\_EN/GPIO33, which will enable the override if it is sampled -low. This pin happens to be connected to a GPIO controlled by the Embedded -Controller (EC), a small microcontroller on the board which handles things like -the keyboard, touchpad, LEDs, and other system level tasks. Software can send a -certain command to the EC, which tells it to pull GPIO33 low on the next boot. - -Although we now have full access according to the IFD permissions, we still -cannot flash the whole chip, due to another protection the firmware uses. -Before software can update the BIOS, it must change the BIOS Write Enable -(BIOSWE) bit in the chipset from 0 to 1. However, if the BIOS Lock Enable (BLE) -bit is also set to 1, then changing the BIOSWE bit triggers a System Management -Interrupt (SMI). This causes the processor to enter System Management Mode -(SMM), a highly privileged x86 execution state which operates transparently to -the operating system. The code that SMM runs is provided by the BIOS, which -checks the BIOSWE bit and sets it back to 0 before returning control to the OS. -This feature is intended to only allow SMM code to update the system firmware. -As the switch to SMM suspends the execution of the OS, it appears to the OS -that the BIOSWE bit was never set to 1. Unfortunately, the BLE bit cannot be -set back to 0 once it is set to 1, so this functionality cannot be disabled -after it is first enabled by the BIOS. - -Older versions of the E6400 BIOS did not set the BLE bit, allowing flashrom to -flash the entire flash chip internally after only setting the descriptor -override. However, more recent versions do set it, so we may have hit a dead -end unless we force downgrade to an older version (though there is a more -convenient method, as we are about to see). - -What if there was a way to sidestep the BIOS Lock entirely? As it turns out, -there is, and it's called the Global SMI Enable (GBL\_SMI\_EN) bit. If it's set -to 1, then the chipset will generate SMIs, such as when we change BIOSWE with -BLE set. If it's 0, then no SMI will be generated, even with the BLE bit set. -On the E6400, GBL\_SMI\_EN is set to 1, and it can be changed back to 0, unlike -the BLE bit. But there still might be one bit in the way, the SMI\_LOCK bit, -which prevents modifications to GBL\_SMI\_EN when SMI\_LOCK is 1. Like the BLE -bit, it cannot be changed back to 0 once it set to 1. But we are in luck, as -the vendor E6400 BIOS leaves SMI\_LOCK unset at 0, allowing us to clear -GBL\_SMI\_EN and disable SMIs, bypassing the BIOS Lock protections. - -There are other possible protection mechanisms that the firmware can utilize, -such as Protected Range Register settings, which apply access permissions to -address ranges of the flash, similar to the IFD. However, the E6400 vendor -firmware does not utilize these, so they will not be discussed. |