About the idle thread stack / read-only segments in the Kernel

Unlike usual kernel stacks, which have an unmapped "guard" page at the end, the idle thread stack (_P0BootStack in ke/i386/boot.S) is not limited, and can unforbiddenly grow until it damages all kernel data.

I first thought that .rdata segment will protect .data from this fate, but it seems that .rdata pages are not read-only. (Bug?)