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Fix issue with emscripten memory out of range #698

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merged 1 commit into from
Aug 19, 2019
Merged

Fix issue with emscripten memory out of range #698

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13 changes: 10 additions & 3 deletions lib/emscripten/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -405,11 +405,18 @@ fn store_module_arguments(ctx: &mut Ctx, args: Vec<&str>) -> (u32, u32) {
(argc as u32 - 1, argv_offset)
}

pub fn emscripten_set_up_memory(memory: &Memory, globals: &EmscriptenGlobalsData) {
pub fn emscripten_set_up_memory(
memory: &Memory,
globals: &EmscriptenGlobalsData,
) -> Result<(), String> {
let dynamictop_ptr = globals.dynamictop_ptr;
let dynamic_base = globals.dynamic_base;

if (dynamictop_ptr / 4) as usize >= memory.view::<u32>().len() {
return Err("dynamictop_ptr beyond memory len".to_string());
}
memory.view::<u32>()[(dynamictop_ptr / 4) as usize].set(dynamic_base);
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I'm very tired, so I kind of missed this, but the bounds check here is something WasmPtr would have done for us and this is kind of new legacy code that we should probably just do right... I suppose I can replace it once this lands on master though

Ok(())
}

pub struct EmscriptenGlobalsData {
Expand Down Expand Up @@ -489,7 +496,7 @@ impl EmscriptenGlobals {
static_top += 16;

let (dynamic_base, dynamictop_ptr) =
get_emscripten_metadata(&module).unwrap_or_else(|| {
get_emscripten_metadata(&module)?.unwrap_or_else(|| {
let dynamictop_ptr = static_alloc(&mut static_top, 4);
(
align_memory(align_memory(static_top) + TOTAL_STACK),
Expand All @@ -513,7 +520,7 @@ impl EmscriptenGlobals {
}
};

emscripten_set_up_memory(&memory, &data);
emscripten_set_up_memory(&memory, &data)?;

let mut null_func_names = vec![];
for (
Expand Down
40 changes: 28 additions & 12 deletions lib/emscripten/src/utils.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -53,15 +53,23 @@ pub fn get_emscripten_memory_size(module: &Module) -> Result<(Pages, Option<Page
/// Assumes values start from the end in this order:
/// Last export: Dynamic Base
/// Second-to-Last export: Dynamic top pointer
pub fn get_emscripten_metadata(module: &Module) -> Option<(u32, u32)> {
let max_idx = &module.info().globals.iter().map(|(k, _)| k).max()?;
let snd_max_idx = &module
pub fn get_emscripten_metadata(module: &Module) -> Result<Option<(u32, u32)>, String> {
let max_idx = match module.info().globals.iter().map(|(k, _)| k).max() {
Some(x) => x,
None => return Ok(None),
};

let snd_max_idx = match module
.info()
.globals
.iter()
.map(|(k, _)| k)
.filter(|k| k != max_idx)
.max()?;
.filter(|k| *k != max_idx)
.max()
{
Some(x) => x,
None => return Ok(None),
};

use wasmer_runtime_core::types::{GlobalInit, Initializer::Const, Value::I32};
if let (
Expand All @@ -74,15 +82,23 @@ pub fn get_emscripten_metadata(module: &Module) -> Option<(u32, u32)> {
..
},
) = (
&module.info().globals[*max_idx],
&module.info().globals[*snd_max_idx],
&module.info().globals[max_idx],
&module.info().globals[snd_max_idx],
) {
Some((
align_memory(*dynamic_base as u32 - 32),
align_memory(*dynamictop_ptr as u32 - 32),
))
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In development profile, there was a subtraction underflow before the index out of bounds error.

let dynamic_base = (*dynamic_base as u32).checked_sub(32).ok_or(format!(
"emscripten unexpected dynamic_base {}",
*dynamic_base as u32
))?;
let dynamictop_ptr = (*dynamictop_ptr as u32).checked_sub(32).ok_or(format!(
"emscripten unexpected dynamictop_ptr {}",
*dynamictop_ptr as u32
))?;
Ok(Some((
align_memory(dynamic_base),
align_memory(dynamictop_ptr),
)))
} else {
None
Ok(None)
}
}

Expand Down