Add a fuzz target for exercising bounds checks with various memory co…

…nfigs

crates/fuzzing/src/generators.rs

@@ -28,7 +28,10 @@ pub use codegen_settings::CodegenSettings;
 pub use config::CompilerStrategy;
 pub use config::{Config, WasmtimeConfig};
 pub use instance_allocation_strategy::InstanceAllocationStrategy;
-pub use memory::{MemoryConfig, NormalMemoryConfig, UnalignedMemory, UnalignedMemoryCreator};
+pub use memory::{
+    HeapImage, MemoryAccesses, MemoryConfig, NormalMemoryConfig, UnalignedMemory,
+    UnalignedMemoryCreator,
+};
 pub use module::ModuleConfig;
 pub use pooling_config::PoolingAllocationConfig;
 pub use single_inst_module::SingleInstModule;

crates/fuzzing/src/generators/config.rs

@@ -172,7 +172,6 @@ impl Config {
             .cranelift_opt_level(self.wasmtime.opt_level.to_wasmtime())
             .consume_fuel(self.wasmtime.consume_fuel)
             .epoch_interruption(self.wasmtime.epoch_interruption)
-            .memory_init_cow(self.wasmtime.memory_init_cow)
             .memory_guaranteed_dense_image_size(std::cmp::min(
                 // Clamp this at 16MiB so we don't get huge in-memory
                 // images during fuzzing.
@@ -259,27 +258,26 @@ impl Config {
                     static_memory_maximum_size: Some(4 << 30), // 4 GiB
                     static_memory_guard_size: Some(2 << 30),   // 2 GiB
                     dynamic_memory_guard_size: Some(0),
+                    dynamic_memory_reserved_for_growth: Some(0),
                     guard_before_linear_memory: false,
+                    memory_init_cow: true,
                 })
             } else {
                 self.wasmtime.memory_config.clone()
             };
 
             match &memory_config {
                 MemoryConfig::Normal(memory_config) => {
-                    cfg.static_memory_maximum_size(
-                        memory_config.static_memory_maximum_size.unwrap_or(0),
-                    )
-                    .static_memory_guard_size(memory_config.static_memory_guard_size.unwrap_or(0))
-                    .dynamic_memory_guard_size(memory_config.dynamic_memory_guard_size.unwrap_or(0))
-                    .guard_before_linear_memory(memory_config.guard_before_linear_memory);
+                    memory_config.apply_to(&mut cfg);
                 }
                 MemoryConfig::CustomUnaligned => {
                     cfg.with_host_memory(Arc::new(UnalignedMemoryCreator))
                         .static_memory_maximum_size(0)
                         .dynamic_memory_guard_size(0)
+                        .dynamic_memory_reserved_for_growth(0)
                         .static_memory_guard_size(0)
-                        .guard_before_linear_memory(false);
+                        .guard_before_linear_memory(false)
+                        .memory_init_cow(false);
                 }
             }
         }

crates/fuzzing/src/generators/memory.rs

@@ -5,6 +5,75 @@ use arbitrary::{Arbitrary, Unstructured};
 use std::ops::Range;
 use wasmtime::{LinearMemory, MemoryCreator, MemoryType};
 
+/// A description of a memory config, image, etc... that can be used to test
+/// memory accesses.
+#[derive(Debug)]
+#[allow(missing_docs)]
+pub struct MemoryAccesses {
+    pub memory_config: NormalMemoryConfig,
+    pub image: HeapImage,
+    pub offset: u32,
+    pub growth: u32,
+}
+
+impl<'a> Arbitrary<'a> for MemoryAccesses {
+    fn arbitrary(u: &mut Unstructured<'a>) -> arbitrary::Result<Self> {
+        Ok(MemoryAccesses {
+            memory_config: u.arbitrary()?,
+            image: u.arbitrary()?,
+            offset: u.arbitrary()?,
+            growth: u.arbitrary()?,
+        })
+    }
+}
+
+/// A memory heap image.
+#[allow(missing_docs)]
+pub struct HeapImage {
+    pub minimum: u32,
+    pub maximum: Option<u32>,
+    pub segments: Vec<(u32, Vec<u8>)>,
+}
+
+impl std::fmt::Debug for HeapImage {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("HeapImage")
+            .field("minimum", &self.minimum)
+            .field("maximum", &self.maximum)
+            .field("segments", &"..")
+            .finish()
+    }
+}
+
+impl<'a> Arbitrary<'a> for HeapImage {
+    fn arbitrary(u: &mut Unstructured<'a>) -> arbitrary::Result<Self> {
+        let minimum = u.int_in_range(0..=4)?;
+        let maximum = if u.arbitrary()? {
+            Some(u.int_in_range(minimum..=10)?)
+        } else {
+            None
+        };
+        let mut segments = vec![];
+        if minimum > 0 {
+            for _ in 0..u.int_in_range(0..=4)? {
+                const WASM_PAGE_SIZE: u32 = 65536;
+                let last_addressable = WASM_PAGE_SIZE * minimum - 1;
+                let offset = u.int_in_range(0..=last_addressable)?;
+                let max_len =
+                    std::cmp::min(u.len(), usize::try_from(last_addressable - offset).unwrap());
+                let len = u.int_in_range(0..=max_len)?;
+                let data = u.bytes(len)?.to_vec();
+                segments.push((offset, data));
+            }
+        }
+        Ok(HeapImage {
+            minimum,
+            maximum,
+            segments,
+        })
+    }
+}
+
 /// Configuration for linear memories in Wasmtime.
 #[derive(Arbitrary, Clone, Debug, Eq, Hash, PartialEq)]
 pub enum MemoryConfig {
@@ -27,7 +96,9 @@ pub struct NormalMemoryConfig {
     pub static_memory_maximum_size: Option<u64>,
     pub static_memory_guard_size: Option<u64>,
     pub dynamic_memory_guard_size: Option<u64>,
+    pub dynamic_memory_reserved_for_growth: Option<u64>,
     pub guard_before_linear_memory: bool,
+    pub memory_init_cow: bool,
 }
 
 impl<'a> Arbitrary<'a> for NormalMemoryConfig {
@@ -38,17 +109,36 @@ impl<'a> Arbitrary<'a> for NormalMemoryConfig {
             static_memory_maximum_size: <Option<u32> as Arbitrary>::arbitrary(u)?.map(Into::into),
             static_memory_guard_size: <Option<u32> as Arbitrary>::arbitrary(u)?.map(Into::into),
             dynamic_memory_guard_size: <Option<u32> as Arbitrary>::arbitrary(u)?.map(Into::into),
+            dynamic_memory_reserved_for_growth: <Option<u32> as Arbitrary>::arbitrary(u)?
+                .map(Into::into),
             guard_before_linear_memory: u.arbitrary()?,
+            memory_init_cow: u.arbitrary()?,
         };
 
         if let Some(dynamic) = ret.dynamic_memory_guard_size {
             let statik = ret.static_memory_guard_size.unwrap_or(2 << 30);
             ret.static_memory_guard_size = Some(statik.max(dynamic));
         }
+
         Ok(ret)
     }
 }
 
+impl NormalMemoryConfig {
+    /// Apply this memory configuration to the given `wasmtime::Config`.
+    pub fn apply_to(&self, config: &mut wasmtime::Config) {
+        config
+            .static_memory_maximum_size(self.static_memory_maximum_size.unwrap_or(0))
+            .static_memory_guard_size(self.static_memory_guard_size.unwrap_or(0))
+            .dynamic_memory_guard_size(self.dynamic_memory_guard_size.unwrap_or(0))
+            .dynamic_memory_reserved_for_growth(
+                self.dynamic_memory_reserved_for_growth.unwrap_or(0),
+            )
+            .guard_before_linear_memory(self.guard_before_linear_memory)
+            .memory_init_cow(self.memory_init_cow);
+    }
+}
+
 /// A custom "linear memory allocator" for wasm which only works with the
 /// "dynamic" mode of configuration where wasm always does explicit bounds
 /// checks.

crates/fuzzing/src/oracles.rs

@@ -16,6 +16,7 @@ pub mod diff_wasmi;
 pub mod diff_wasmtime;
 pub mod dummy;
 pub mod engine;
+pub mod memory;
 mod stacks;
 
 use self::diff_wasmtime::WasmtimeInstance;