Boot: Check TMD validity before reading from TMD

[JosJuice]

Otherwise Dolphin crashes when trying to boot a Wii game with an invalid TMD.

[shuffle2]

What are such games? Does it just refuse to boot after this?

[JosJuice]

All retail releases have valid TMDs. Invalid TMDs are mostly a concern for VolumeDirectory/DirectoryBlob. Right now, they always have invalid TMDs. We currently workaround that by never calling EmulatedBS2_Wii for them (PR #5400), but we did have crashes here before that workaround was added. With the VolumeDirectory-to-DirectoryBlob redesign (PR #5573), it will be possible for the user to supply a valid TMD or not, and the workaround of never calling EmulatedBS2_Wii will be dropped.

Yes, it'll refuse to boot. More specifically, we end up here:

dolphin/Source/Core/Core/Core.cpp

Line 563 in 1f30bd1

return;

[shuffle2]

So is booting dev signed stuff broken?

[JosJuice]

I'm not sure what dev-signed discs are like, and I can't check because I don't have any. I would assume they have TMDs, but that's just a guess.

[leoetlino]

We don't really use anything from the TMD, other than to get the required IOS version, and the TMD is handled the same way on dev consoles as on retail consoles (as the IOSes are the same).

[shuffle2]

So I guess IsValid is more like Exists?

[leoetlino]

Sort of, IsValid() will return false if the TMD size isn't at least as large as the base TMD header + content entries