Setting NVRAM default values without recompilation? about firmadyne HOT 3 CLOSED

Yes, they can be put there as well instead of directly into the code. See https://github.com/firmadyne/firmadyne/blob/master/scripts/fixImage.sh for examples of where this is used.

However, generally there's not a single key-value pair that is necessary for the system to boot, but tens if not hundreds of key-value pairs. Thus, the easiest way to get a new firmware working is to figure out where the manufacturer stores the default values (e.g. after resetting the system), and add it to NVRAM_DEFAULTS_PATH in https://github.com/firmadyne/libnvram/blob/master/config.h .

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@ddcc Can you provide some examples of where manufacturer stores default nvram values? Or how you would go about finding out? find . | grep -i nvram on the target filesystem only returned the nvram binary and library. Thanks

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Unfortunately, it's a somewhat manual process of figuring out the NVRAM is being handled, and then looking to see where the values are coming from. If you look at the linked config.h file, sometimes the default values are stored in a file on the filesystem (PATH), or sometimes they are key-value pairs stored as a table in a shared symbol (TABLE). You probably want to search inside some of the binaries / libraries, either using something basic like strings <foo> | grep <bla>.

Alternatively, you can work backwards by figuring out where the boot process / program of interest is crashing, examine the last couple of NVRAM key/value pairs that were requested, overriding them with different values and seeing if you get farther. Additionally, disassembling / decompiling them and looking for anything interesting makes this process a lot easier.

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