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use use_stack, actualy add text

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Lotte Steenbrink 2021-01-22 15:59:13 +01:00
parent 5372bfa0fe
commit a0caf51682
2 changed files with 61 additions and 5 deletions
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12
advanced/firmware/src/bin/stack_overflow.rs
View file

@ -11,7 +11,7 @@ fn main() -> ! {
dk::init().unwrap();
log::info!("provoking stack overflow...");
spam();
spam(0);
loop {
asm::bkpt();
@ -19,14 +19,16 @@ fn main() -> ! {
}
#[inline(never)]
fn spam() {
fn spam(n: u32) {
// allocate and initialize 4 kilobytes of stack memory to provoke stack overflow
let use_stack = [0xAA_u32; 1024];
let use_stack = [n; 1024];
log::info!(
"address of current `use_stack`: {:?}",
"address of current `use_stack` at recursion depth {:?}: {:?}",
use_stack[1023], // "use" use_stack to prevent it from being optimized out
&use_stack as *const u32
);
spam(); // infinite recursion
let next = n + 1;
spam(next); // infinite recursion
}

54
embedded-workshop-book/src/stack-overflow-protection.md Normal file
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@ -0,0 +1,54 @@
# Stack Overflow Protection
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.
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.
🔎 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].
You can see this in action in the `stack_overflow.rs` file that can be found in `advanced/firmware/src/bin/`:
``` rust
{{#include ../../advanced/firmware/src/bin/stack_overflow.rs}}
```
The `spam()` function allocates data on the stack until the stack boundaries are reached.
✅ Run `stack_overflow.rs`
You should see output similar to this:
``` console
(...)
(HOST) INFO flashing program (32.68 KiB)
(HOST) INFO success!
────────────────────────────────────────────────────────────────────────────────
INFO:stack_overflow -- provoking stack overflow...
INFO:stack_overflow -- address of current `use_stack` at recursion depth 0: 0x2003aec0
INFO:stack_overflow -- address of current `use_stack` at recursion depth 1: 0x20039e50
(...)
INFO:stack_overflow -- address of current `use_stack` at recursion depth 10: 0x20030a60
INFO:stack_overflow -- address of current `use_stack` at recursionstack backtrace:
0: HardFaultTrampoline
<exception entry>
1: ???
error: the stack appears to be corrupted beyond this point
(HOST) ERROR the program has overflowed its stack
```
❗️ `flip-link` is a third-party tool, so make sure you've installed it through `cargo install flip-link`
To see how we've activated `flip-link`, take a look at `advanced/firmware/.cargo/config.toml`:
``` toml
{{#include ../../advanced/firmware/.cargo/config.toml::7}}
```
There, we've configured `flip-link` as the linker to be used for all ARM targets.
If you'd like to use `flip-link` in your own projects, this is all you need to add!
🔎 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.
[`flip-link`]: https://github.com/knurling-rs/flip-link
[`flip-link` README]: https://github.com/knurling-rs/flip-link/blob/main/README.md