This is meant as a little update on one of the projects I've been working on. I'm kinda stuck now. I have a suspicion of what the problem is. I thought that maybe if I write a post about it, me or someone else will have an idea on how to get this working.
The goal is to run native homebrew executables on WP7
This has not been done yet. All apps are Silverlight apps that are compiled as DLL and run by Taskhost.exe with least privileges. All other executables are signed by Microsoft. Executables that are compiled as ARM executable cannot be started.
The angle is to create a certificate that allows to sign a WP7 executable. Then add that to the appropriate certificate store. Create an executable. Sign it with the private key. Load it onto a WP7 device. Copy it to the Windows folder. Use an OEM driver to launch the executable.
First I did research on the certificate stores. I can now with certainty state that there are 4 certificate stores:
- Code Integrity
After a lot of research I finally got complete read/write access to all of these stores. The Code Integrity store contains all the certificates that are used by the Loader Verifier to verify the executable that is being launched. When the device is launched for the first time, the certificates that are in \Windows\ciroots.p7b are installed to that certificate store. These certificates have these properties:
Key Usage = 0x86 = Digital Signature, Certificate Signing, Off-line CRL Signing, CRL Signing
Entended Key Usage = Code Signing (18.104.22.168.22.214.171.124.3) + Unknown key usage (126.96.36.199.4.1.3188.8.131.52)
So I used OpenSSL to create such an certificate (with private key) for myself. And I installed the certificate in the Code Integrity store.
I then used VS2008 to create a completely barebone executable (ARMv4 Console app with only Sleep(-1) in the Main). I signed it with SignTool from Microsoft.
I loaded the executable to my device and I copied it to the \Windows folder (I think the policies restrict executing to only from that folder, but I'm not sure about that).
I use the Samsung driver to launch the executable, because I need at least Standard Rights to launch an executable. The Samsung driver has Elevated Rights. My own app has only Least Privileges. Using the Samsung driver does not return any success or fail codes. But looking at the Running Processes list, I don't see my Test.exe running. It should be, because the main thread is put to sleep infinitely.
So why is this not working?
Well, I have a guess. I think it's the policies that bind the certificates in the Code Integrity store to the different accounts/chambers. In the \Windows folder there are a lot of policy xml-files. On fist boot, these are merged into PolicyCommit.xml and then compiled to policydb.vol. When the Loader Verifier (lvmod.dll) loads an executable, it queries the policies to determine access rights and chamber for that executable. The policies that matter in this context are defined in 8314B832-8D03-444f-9A2A-1EF6FADCC3B8.policy.xml. It's an xml-file that basically says this:
Microsoft Mobile Device Privileged PCA - ced778d7bb4cb41d26c40328cc9c0397926b4eea - not used in this context Microsoft Mobile Device TCB PCA - 88bcaec267ef8b366c6e6215ac4028e7a1be2deb - honored by System Identity Group Microsoft Mobile Device Unprivileged PCA - 1c8229f5c8d6e256bdcb427cc5521ec2f8ff011a - honored by Standard Right Identity Group Microsoft Mobile Device VSD PCA - 91b318116f8897d2860733fdf757b93345373574 - not used in this context VeriSign Mobile Root Authority for Microsoft - 069dbcca9590d1b5ed7c73de65795348e58d4ae3 - honored by LPC Identity Group