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55 lines
3 KiB
Markdown
55 lines
3 KiB
Markdown
# Stack Overflow Protection
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The `firmware` crate in which we developed our advanced workshop solutions (i.e. `advanced/firmware`) uses our open-source [`flip-link`] tool for zero-cost stack overflow protection.
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This means that your application will warn you by crashing if you accidentally overreach the boundaries of your application's stack instead of running into *undefined behavior* and behaving erratically in irreproducible ways. This memory protection mechanism comes at no additional computational or memory-usage cost.
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🔎 For a detailed description of how `flip-link` and Stack Overflows in bare metal Rust in general work, please refer to the [`flip-link` README].
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You can see this in action in the `stack_overflow.rs` file that can be found in `advanced/firmware/src/bin/`:
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``` rust
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{{#include ../../advanced/firmware/src/bin/stack_overflow.rs}}
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```
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The `spam()` function allocates data on the stack until the stack boundaries are reached.
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✅ Run `stack_overflow.rs`
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You should see output similar to this (the program output between the horizontal bars might be missing):
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``` console
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(HOST) INFO flashing program (35.25 KiB)
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(HOST) INFO success!
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────────────────────────────────────────────────────────────────────────────────
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INFO:stack_overflow -- provoking stack overflow...
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INFO:stack_overflow -- address of current `use_stack` at recursion depth 0: 0x2003aec0
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INFO:stack_overflow -- address of current `use_stack` at recursion depth 1: 0x20039e50
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(...)
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INFO:stack_overflow -- address of current `use_stack` at recursion depth 10: 0x20030a60
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INFO:stack_overflow -- address of current `use_stack` at recursion
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────────────────────────────────────────────────────────────────────────────────
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stack backtrace:
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0: HardFaultTrampoline
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<exception entry>
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(HOST) WARN call stack was corrupted; unwinding could not be completed
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(HOST) ERROR the program has overflowed its stack
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```
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❗️ `flip-link` is a third-party tool, so make sure you've installed it through `cargo install flip-link`
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To see how we've activated `flip-link`, take a look at `advanced/firmware/.cargo/config.toml`:
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``` toml
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{{#include ../../advanced/firmware/.cargo/config.toml::7}}
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```
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There, we've configured `flip-link` as the linker to be used for all ARM targets.
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If you'd like to use `flip-link` in your own projects, this is all you need to add!
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🔎 Note: if you try to run `stack_overflow.rs` *without* `flip-link` enabled, you might see varying behavior depending on the `rustc` version you're using, timing and pure chance. This is because undefined behavior triggered by the program may change between `rustc` releases.
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[`flip-link`]: https://github.com/knurling-rs/flip-link
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[`flip-link` README]: https://github.com/knurling-rs/flip-link/blob/main/README.md
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