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Catching Stack Overflows

Protecting from stack overflows works in a similar way. The stack grows from high address to low address. To detect a stack overflow, the memory immediately preceding the stack should have less than read/write access. For example, the stack could be placed following the code section or in a region separated from other regions by at least one page.

Example:

Region  FirstPage  0     4k  RAM  Assign 
Region  LowMem     4k  636k  RAM  Assign 
Region  HighMem    1M    3M  RAM  Assign 

Virtual ProgMem    4M             // for code and data 
Virtual StackMem   5M             // for the stack 
Virtual HeapMem    6M             // for the heap which gets 

FillRAM HeapMem                   // all remaining memory 

... 
Locate  Stack  S  StackMem->LowMem  16k 
Locate  Heap   H  HeapMem

Both the stack and the heap are placed in separate virtual regions, completely isolating them from other program entities. Any stack overflow will cause the stack pointer to leave region StackMem and will trigger a page fault.

Advanced Topics

Catching NULL Pointer Assignments

Running without Run-Time System