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by BradSwain
465 days ago
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> while stack clashing was considered and is a theoretical possibility — denial of service was considered to be the realistic impact. In many contexts, regular process failure is still a vulnerability. And the stack is (usually) tiny compared to other resources. It doesn't take that many nested calls to get to the bottom of the stack. At least compared to trying to exhaust the heap or keep the CPU busy long enough to cause DoS. |
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This is sort of amusingly backwards. On embedded systems where I live, stacks are huge. Thread stacks of 4-16k are routinely the largest single objects the kernel sees in Zephyr. And yes, lots of RTOS apps disallow recursion (Zephyr doesn't, but does gate its use in the core system behind build-time config that can be turned off) because in that world it's hard to provide the guarantees you can get with a 64 bit mmu environment.
But if you are on a modern 64 bit OS, no: stacks are enormous. Many megabytes of mapping is routine. Obviously that's not all going to be faulted in, and most threads won't ever use more than a few kilobytes. But the region reserved for recursive use is extremely large, and unlikely to overflow except in a well-crafted deliberate attack (and even then it generally requires a few bugs in the code; most recursive algorithms are bounded by e.g. maximum tree height or something that is O(logN) and thus can't overflow).