Just an example of a well-known technique to detect memory tampering via Windows Working Sets.
Non-writable pages are being shared among processes that need them. Each process reads the same copy.
Once one process modifies the protection of a page to write to it, the system will copy the page and serve the process its own copy. Once in this state, the Shared member of the PSAPI_WORKING_SET_INFORMATION (returned by QueryWorkingSet(Ex) API(s)) will be FALSE (0).
A process can check his .text section (or any non-writable section) by querying his Working Set (using QueryWorkingSet(Ex) API(s)) and checking the Shared member (and may have use of the ShareCount member).
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Running without a debugger
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Running under a debugger (you need to place a breakpoint somewhere in
main.cmain()routine)
The page RVA in the screenshot above would be 0x5000, once you load the built sample into your favorite disassembler you can notice that the page at RVA 0x5000 is where you put the breakpoint.
Have fun 🏴☠️