Avoid dependency on Wasmer's Bytes to Pages conversion

packages/vm/src/wasm_backend/store.rs

@@ -1,17 +1,24 @@
+use std::convert::TryInto;
 #[cfg(feature = "cranelift")]
 use wasmer::Cranelift;
 #[cfg(not(feature = "cranelift"))]
 use wasmer::Singlepass;
 use wasmer::{
-    Bytes, Engine, Pages, Store, Target,
+    Engine, Pages, Store, Target,
     Tunables as ReferenceTunables, /* See https://github.com/wasmerio/wasmer/issues/1872 */
-    JIT,
+    JIT, WASM_PAGE_SIZE,
 };
 
 use crate::size::Size;
 
 use super::limiting_tunables::LimitingTunables;
 
+/// WebAssembly linear memory objects have sizes measured in pages. Each page
+/// is 65536 (2^16) bytes. In WebAssembly version 1, a linear memory can have at
+/// most 65536 pages, for a total of 2^32 bytes (4 gibibytes).
+/// https://github.com/WebAssembly/memory64/blob/master/proposals/memory64/Overview.md
+const MAX_WASM_MEMORY: usize = 4 * 1024 * 1024 * 1024;
+
 /// Created a store with the default compiler and the given memory limit (in bytes)
 /// If memory_limit is None, no limit is applied.
 pub fn make_store(memory_limit: Option<Size>) -> Store {
@@ -42,9 +49,13 @@ pub fn make_store_headless(memory_limit: Option<Size>) -> Store {
 fn make_store_with_engine(engine: &dyn Engine, memory_limit: Option<Size>) -> Store {
     match memory_limit {
         Some(limit) => {
-            let pages = Pages::from(Bytes(limit.0));
+            let capped = std::cmp::max(limit.0, MAX_WASM_MEMORY);
+            // round down to ensure the limit is less than or equal to the config
+            let pages: u32 = (capped / WASM_PAGE_SIZE)
+                .try_into()
+                .expect("Value must be <= 4 GiB/64KiB, i.e. fit in uint32. This is a bug.");
             let base = ReferenceTunables::for_target(&Target::default());
-            let tunables = LimitingTunables::new(base, pages);
+            let tunables = LimitingTunables::new(base, Pages(pages));
             Store::new_with_tunables(engine, tunables)
         }
         None => Store::new(engine),