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</pre></div><pre class="rust"><code><span class="doccomment">//! Simple `mmap`ed runtime.
//!
//! This runtime supports adding code to executable pages and turn the added code into user
//! specified function pointer.
</span><span class="kw">use </span>nix::sys::mman::{mmap, mprotect, munmap, MapFlags, ProtFlags};
<span class="attr">#[cfg(not(target_os = <span class="string">"linux"</span>))]
</span><span class="macro">compile_error!</span>(<span class="string">"This runtime is only supported on linux"</span>);
<span class="doccomment">/// A simple `mmap`ed runtime with executable pages.
</span><span class="kw">pub struct </span>Runtime {
buf: <span class="kw-2">*mut </span>u8,
len: usize,
idx: usize,
}
<span class="kw">impl </span>Runtime {
<span class="doccomment">/// Create a new [Runtime].
///
/// # Panics
///
/// Panics if the `mmap` call fails.
</span><span class="kw">pub fn </span>new() -> Runtime {
<span class="comment">// Allocate a single page.
</span><span class="kw">let </span>len = core::num::NonZeroUsize::new(<span class="number">4096</span>).expect(<span class="string">"Value is non zero"</span>);
<span class="kw">let </span>buf = <span class="kw">unsafe </span>{
mmap(
<span class="prelude-val">None</span>,
len,
ProtFlags::PROT_NONE,
MapFlags::MAP_PRIVATE | MapFlags::MAP_ANONYMOUS,
<span class="number">0</span>, <span class="comment">/* fd */
</span><span class="number">0</span>, <span class="comment">/* off */
</span>)
.expect(<span class="string">"Failed to mmap runtime code page"</span>) <span class="kw">as </span><span class="kw-2">*mut </span>u8
};
Runtime {
buf,
len: len.get(),
idx: <span class="number">0</span>,
}
}
<span class="doccomment">/// Add the block of `code` to the runtime and a get function pointer of type `F`.
///
/// # Panics
///
/// Panics if the `code` does not fit on the `mmap`ed pages or is empty.
///
/// # Safety
///
/// The code added must fulfill the ABI of the specified function `F` and the returned function
/// pointer is only valid until the [`Runtime`] is dropped.
///
/// # Examples
///
/// ```
/// let mut rt = juicebox_asm::Runtime::new();
///
/// let code = [ 0x90 /* nop */, 0xc3 /* ret */ ];
/// let nop = unsafe { rt.add_code::<extern "C" fn()>(&code) };
///
/// nop();
/// ```
</span><span class="kw">pub unsafe fn </span>add_code<F>(<span class="kw-2">&mut </span><span class="self">self</span>, code: <span class="kw">impl </span>AsRef<[u8]>) -> F {
<span class="comment">// Get pointer to start of next free byte.
</span><span class="macro">assert!</span>(<span class="self">self</span>.idx < <span class="self">self</span>.len, <span class="string">"Runtime code page full"</span>);
<span class="kw">let </span>fn_start = <span class="self">self</span>.buf.add(<span class="self">self</span>.idx);
<span class="comment">// Copy over code.
</span><span class="kw">let </span>code = code.as_ref();
<span class="macro">assert!</span>(!code.is_empty(), <span class="string">"Adding empty code not supported"</span>);
<span class="macro">assert!</span>(
code.len() <= (<span class="self">self</span>.len - <span class="self">self</span>.idx),
<span class="string">"Code does not fit on the runtime code page"
</span>);
<span class="self">self</span>.unprotect();
<span class="kw">unsafe </span>{ std::ptr::copy_nonoverlapping(code.as_ptr(), fn_start, code.len()) };
<span class="self">self</span>.protect();
<span class="comment">// Increment index to next free byte.
</span><span class="self">self</span>.idx += code.len();
<span class="comment">// Return function to newly added code.
</span><span class="kw">unsafe </span>{ <span class="self">Self</span>::as_fn::<F>(fn_start) }
}
<span class="doccomment">/// Dump the code added so far to the runtime into a file called `jit.asm` in the processes
/// current working directory.
///
/// The code can be inspected with a disassembler as for example `ndiasm` from
/// [nasm.us](https://nasm.us/index.php).
/// ```sh
/// ndisasm -b 64 jit.asm
/// ```
///
/// # Panics
///
/// Panics if writing the file failed.
</span><span class="kw">pub fn </span>dump(<span class="kw-2">&</span><span class="self">self</span>) {
<span class="macro">assert!</span>(<span class="self">self</span>.idx <= <span class="self">self</span>.len);
<span class="kw">let </span>code = <span class="kw">unsafe </span>{ core::slice::from_raw_parts(<span class="self">self</span>.buf, <span class="self">self</span>.idx) };
std::fs::write(<span class="string">"jit.asm"</span>, code).expect(<span class="string">"Failed to write file"</span>);
}
<span class="doccomment">/// Reinterpret the block of code pointed to by `fn_start` as `F`.
</span><span class="attr">#[inline]
</span><span class="kw">unsafe fn </span>as_fn<F>(fn_start: <span class="kw-2">*mut </span>u8) -> F {
<span class="kw">unsafe </span>{ std::mem::transmute_copy(<span class="kw-2">&</span>fn_start) }
}
<span class="doccomment">/// Add write protection the underlying code page(s).
///
/// # Panics
///
/// Panics if the `mprotect` call fails.
</span><span class="kw">fn </span>protect(<span class="kw-2">&mut </span><span class="self">self</span>) {
<span class="kw">unsafe </span>{
<span class="comment">// Remove write permissions from code page and allow to read-execute from it.
</span>mprotect(
<span class="self">self</span>.buf.cast(),
<span class="self">self</span>.len,
ProtFlags::PROT_READ | ProtFlags::PROT_EXEC,
)
.expect(<span class="string">"Failed to RX mprotect runtime code page"</span>);
}
}
<span class="doccomment">/// Remove write protection the underlying code page(s).
///
/// # Panics
///
/// Panics if the `mprotect` call fails.
</span><span class="kw">fn </span>unprotect(<span class="kw-2">&mut </span><span class="self">self</span>) {
<span class="kw">unsafe </span>{
<span class="comment">// Add write permissions to code page.
</span>mprotect(<span class="self">self</span>.buf.cast(), <span class="self">self</span>.len, ProtFlags::PROT_WRITE)
.expect(<span class="string">"Failed to W mprotect runtime code page"</span>);
}
}
}
<span class="kw">impl </span>Drop <span class="kw">for </span>Runtime {
<span class="doccomment">/// Unmaps the code page. This invalidates all the function pointer returned by
/// [`Runtime::add_code`].
</span><span class="kw">fn </span>drop(<span class="kw-2">&mut </span><span class="self">self</span>) {
<span class="kw">unsafe </span>{
munmap(<span class="self">self</span>.buf.cast(), <span class="self">self</span>.len).expect(<span class="string">"Failed to munmap runtime"</span>);
}
}
}
<span class="attr">#[cfg(test)]
</span><span class="kw">mod </span>test {
<span class="kw">use super</span>::<span class="kw-2">*</span>;
<span class="attr">#[test]
</span><span class="kw">fn </span>test_code_max_size() {
<span class="kw">let </span><span class="kw-2">mut </span>rt = Runtime::new();
<span class="kw">let </span>code = [<span class="number">0u8</span>; <span class="number">4096</span>];
<span class="kw">unsafe </span>{
rt.add_code::<<span class="kw">extern </span><span class="string">"C" </span><span class="kw">fn</span>()>(code);
}
}
<span class="attr">#[test]
#[should_panic]
</span><span class="kw">fn </span>test_code_max_size_plus_1() {
<span class="kw">let </span><span class="kw-2">mut </span>rt = Runtime::new();
<span class="kw">let </span>code = [<span class="number">0u8</span>; <span class="number">4097</span>];
<span class="kw">unsafe </span>{
rt.add_code::<<span class="kw">extern </span><span class="string">"C" </span><span class="kw">fn</span>()>(code);
}
}
<span class="attr">#[test]
#[should_panic]
</span><span class="kw">fn </span>test_code_max_size_plus_1_2() {
<span class="kw">let </span><span class="kw-2">mut </span>rt = Runtime::new();
<span class="kw">let </span>code = [<span class="number">0u8</span>; <span class="number">4096</span>];
<span class="kw">unsafe </span>{
rt.add_code::<<span class="kw">extern </span><span class="string">"C" </span><span class="kw">fn</span>()>(code);
}
<span class="kw">let </span>code = [<span class="number">0u8</span>; <span class="number">1</span>];
<span class="kw">unsafe </span>{
rt.add_code::<<span class="kw">extern </span><span class="string">"C" </span><span class="kw">fn</span>()>(code);
}
}
<span class="attr">#[test]
#[should_panic]
</span><span class="kw">fn </span>test_empty_code() {
<span class="kw">let </span><span class="kw-2">mut </span>rt = Runtime::new();
<span class="kw">let </span>code = [<span class="number">0u8</span>; <span class="number">0</span>];
<span class="kw">unsafe </span>{
rt.add_code::<<span class="kw">extern </span><span class="string">"C" </span><span class="kw">fn</span>()>(code);
}
}
}
</code></pre></div></section></main></body></html>
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