Plundervolt "fix" disables undervolting at BIOS level - any way to reverse?

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New owner of a Dell G7 7700. The laptop's got guts and I really like that it's packing a 2070, but it's a hot mess in need of an undervolt - and apparently that's no longer allowed.

I fired up Intel XTU and the undervolt settings are greyed out. Did some digging and found that Dell (and many other OEMs) are locking voltage modification to mitigate Plundervolt exploits.

As this laptop is a very new model, I don't seem to have the option to roll back to an older BIOS from before the lock. There are only two BIOS available from Dell, and neither of them have voltage tweaks enabled.

I've found some work by enterprising Dell XPS owners in modding their BIOS directly to enable the feature again. It's a single flag that needs flipped from a 1 to a 0, and while it seems a simple thing, I've never done that kind of work to a BIOS and am a bit scared of bricking my machine.

Does anyone have experience with this kind of thing?
 
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Managed to do it!

It involved extracting the BIOS file, then extracting a file from that to find the bits that needed flipped.

After that I used a utility called modgrubshell to change those registers and, viola! Undervolting is available again in XTU.

Suck it, Dell. And Intel.
 

rive22

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Thanks guys. My Dell XPS 15 feels much more like a desktop now. I was lucky though, I didn't have to install the mod in this case, all I had to do was reset the bios to factory settings and the voltage unlocked. :D
 
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CEO_OF_CBT

Limp Gawd
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Managed to do it!

It involved extracting the BIOS file, then extracting a file from that to find the bits that needed flipped.

After that I used a utility called modgrubshell to change those registers and, viola! Undervolting is available again in XTU.

Suck it, Dell. And Intel.


can you provide a more detailed instruction on how to do this?
 

CEO_OF_CBT

Limp Gawd
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It does! That's why I say in my post you gotta disable it before you can run modgrubshell off the USB stick.


Ok nvm I re-read the entire thing

Seems like the secureboot is only preventing the usb stick from booting up

Then bootguard/bios guard isn't tripped because setup_var usb only modifies settings that are invisible to the BIOS GUI.

I thought it's some sort of modification that changes bios contents that's outside of the bootguard protected regions.



I wonder what this actually changes in the bios though, wonder if it's enabling/disabling SGX feature (the vulnerability target of plundervolt).
 
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Ok nvm I re-read the entire thing

Seems like the secureboot is only preventing the usb stick from booting up

Then bootguard/bios guard isn't tripped because setup_var usb only modifies settings that are invisible to the BIOS GUI.

I thought it's some sort of modification that changes bios contents that's outside of the bootguard protected regions.



I wonder what this actually changes in the bios though, wonder if it's enabling/disabling SGX feature (the vulnerability target of plundervolt).
Couldn't say. This was my first dive into modding a BIOS. The guy who figured it out in that Reddit thread was doing it because MacOS uses the advanced processor power control features that are locked behind those "CFG Lock" and "OC lock" variables, so fiddling with them is a common step when building a hackintosh. Given that Mac systems can access those controls with software I have to assume the Plundervolt vulnerability functions in a similar way.
 

CEO_OF_CBT

Limp Gawd
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Couldn't say. This was my first dive into modding a BIOS. The guy who figured it out in that Reddit thread was doing it because MacOS uses the advanced processor power control features that are locked behind those "CFG Lock" and "OC lock" variables, so fiddling with them is a common step when building a hackintosh. Given that Mac systems can access those controls with software I have to assume the Plundervolt vulnerability functions in a similar way.
This is not bios modding, just poking through settings that are hidden from adjustment due to omitting bios GUI
 

rive22

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It's definitely worth doing even if modding the bios is what it takes. Instead of throttling to 2.9Ghz on my XPS 15 on all cores from hitting 99c, I now get 3.7ghz fully loaded on all cores while riding smooth in the 70-80's. I was able push it further to get 3.9 on all cores at the same temps, but I use this machine for work and I need to make sure it's stable so I dialed back the undervolt to more common safer levels.
 

CEO_OF_CBT

Limp Gawd
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It's definitely worth doing even if modding the bios is what it takes. Instead of throttling to 2.9Ghz on my XPS 15 on all cores from hitting 99c, I now get 3.7ghz fully loaded on all cores while riding smooth in the 70-80's. I was able push it further to get 3.9 on all cores at the same temps, but I use this machine for work and I need to make sure it's stable so I dialed back the undervolt to more common safer levels.

You can't mod bios contents that is inside protected by the bootguard/bios guard region.
 
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