Validate reservation size in Config (#15209)

This commit fixes some possible `unwrap()`s with the new `MemoryRequest`
type where some values were coerced from `u64` to `usize` in a way that
could panic. This commit moves validation into `Config` to make these
conversions always work and seems like a reasonable place to get an
error anyway.

Author: alexcrichton

crates/wasmtime/src/config.rs

@@ -2919,13 +2919,17 @@ impl Config {
         }
 
         // Validate that the configuration of reservation/guards is sensible
-        // enough to ever possibly actually get allocated. If this overflows a
-        // u64 then there's no hope.
+        // enough to ever possibly actually get allocated. If this doesn't fit
+        // in the target's address space then there's no hope.
         let guard_regions = if tunables.guard_before_linear_memory {
             2
         } else {
             1
         };
+        let max_size = match self.compiler_target().pointer_width() {
+            Ok(width) if width.bits() < 64 => (1 << width.bits()) - 1,
+            _ => u64::MAX,
+        };
         for (what, reservation, guard_size) in [
             (
                 "memory",
@@ -2941,11 +2945,11 @@ impl Config {
             if guard_size
                 .checked_mul(guard_regions)
                 .and_then(|g| g.checked_add(reservation))
-                .is_none()
+                .is_none_or(|size| size > max_size)
             {
                 bail!(
                     "`{what}_reservation` ({reservation}) plus `{what}_guard_size` \
-                     ({guard_size}) overflows"
+                     ({guard_size}) overflows the target's address space"
                 );
             }
         }

tests/all/pulley.rs

@@ -58,6 +58,21 @@ fn pulley_wrong_architecture_is_rejected() -> Result<()> {
     Ok(())
 }
 
+#[test]
+fn memory_tunables_must_fit_in_target_address_space() -> Result<()> {
+    let mut config = Config::new();
+    config.target("pulley32")?;
+    config.memory_reservation(1 << 32);
+    assert!(Engine::new(&config).is_err());
+    config.memory_reservation(0).memory_guard_size(1 << 32);
+    assert!(Engine::new(&config).is_err());
+
+    config.target("pulley64")?;
+    config.memory_reservation(1 << 32);
+    Engine::new(&config)?;
+    Ok(())
+}
+
 // CLI subcommands should support `--target`
 #[test]
 #[cfg(not(miri))]