fix: expand memory on reading prev. untouched location (#1887)

* fix: expand memory on reading prev. untouched location

Memory is expanded by word when accessing previously untouched memory word ([relevant docs](https://docs.soliditylang.org/en/v0.8.13/introduction-to-smart-contracts.html#storage-memory-and-the-stack)). That applies to read operation on memory too.

* fix: properly auto-expand memory on read/write

* test: add tests for memory expansion on access

Removed a couple of tests for write beyond capacity.
This is because memory is now auto expanded during write.

packages/vm/src/evm/memory.ts

@@ -47,6 +47,8 @@ export default class Memory {
       return
     }
 
+    this.extend(offset, size)
+
     assert(value.length === size, 'Invalid value size')
     assert(offset + size <= this._store.length, 'Value exceeds memory capacity')
     assert(Buffer.isBuffer(value), 'Invalid value type')
@@ -63,6 +65,8 @@ export default class Memory {
    * @param size - How many bytes to read
    */
   read(offset: number, size: number): Buffer {
+    this.extend(offset, size)
+
     const returnBuffer = Buffer.allocUnsafe(size)
     // Copy the stored "buffer" from memory into the return Buffer
 

packages/vm/src/evm/opcodes/functions.ts

@@ -458,7 +458,6 @@ export const handlers: Map<number, OpHandler> = new Map([
         const data = getDataSlice(runState.eei.getCallData(), dataOffset, dataLength)
         const memOffsetNum = memOffset.toNumber()
         const dataLengthNum = dataLength.toNumber()
-        runState.memory.extend(memOffsetNum, dataLengthNum)
         runState.memory.write(memOffsetNum, dataLengthNum, data)
       }
     },
@@ -480,7 +479,6 @@ export const handlers: Map<number, OpHandler> = new Map([
         const data = getDataSlice(runState.eei.getCode(), codeOffset, dataLength)
         const memOffsetNum = memOffset.toNumber()
         const lengthNum = dataLength.toNumber()
-        runState.memory.extend(memOffsetNum, lengthNum)
         runState.memory.write(memOffsetNum, lengthNum, data)
       }
     },
@@ -506,7 +504,6 @@ export const handlers: Map<number, OpHandler> = new Map([
         const data = getDataSlice(code, codeOffset, dataLength)
         const memOffsetNum = memOffset.toNumber()
         const lengthNum = dataLength.toNumber()
-        runState.memory.extend(memOffsetNum, lengthNum)
         runState.memory.write(memOffsetNum, lengthNum, data)
       }
     },
@@ -549,7 +546,6 @@ export const handlers: Map<number, OpHandler> = new Map([
         const data = getDataSlice(runState.eei.getReturnData(), returnDataOffset, dataLength)
         const memOffsetNum = memOffset.toNumber()
         const lengthNum = dataLength.toNumber()
-        runState.memory.extend(memOffsetNum, lengthNum)
         runState.memory.write(memOffsetNum, lengthNum, data)
       }
     },
@@ -652,7 +648,8 @@ export const handlers: Map<number, OpHandler> = new Map([
     0x51,
     function (runState) {
       const pos = runState.stack.pop()
-      const word = runState.memory.read(pos.toNumber(), 32)
+      const posNum = pos.toNumber()
+      const word = runState.memory.read(posNum, 32)
       runState.stack.push(new BN(word))
     },
   ],
@@ -663,7 +660,6 @@ export const handlers: Map<number, OpHandler> = new Map([
       const [offset, word] = runState.stack.popN(2)
       const buf = word.toArrayLike(Buffer, 'be', 32)
       const offsetNum = offset.toNumber()
-      runState.memory.extend(offsetNum, 32)
       runState.memory.write(offsetNum, 32, buf)
     },
   ],
@@ -678,7 +674,6 @@ export const handlers: Map<number, OpHandler> = new Map([
       // the types are wrong
       const buf = Buffer.from([byte.andln(0xff) as unknown as number])
       const offsetNum = offset.toNumber()
-      runState.memory.extend(offsetNum, 1)
       runState.memory.write(offsetNum, 1, buf)
     },
   ],

packages/vm/src/evm/opcodes/util.ts

@@ -223,7 +223,6 @@ export function writeCallOutput(runState: RunState, outOffset: BN, outLength: BN
       dataLength = returnData.length
     }
     const data = getDataSlice(returnData, new BN(0), new BN(dataLength))
-    runState.memory.extend(memOffset, dataLength)
     runState.memory.write(memOffset, dataLength, data)
   }
 }

packages/vm/tests/api/evm/memory.spec.ts

@@ -5,7 +5,6 @@ tape('Memory', (t) => {
   const m = new Memory()
   t.test('should have 0 capacity initially', (st) => {
     st.equal(m._store.length, 0)
-    st.throws(() => m.write(0, 3, Buffer.from([1, 2, 3])), /capacity/)
     st.end()
   })
 
@@ -25,11 +24,6 @@ tape('Memory', (t) => {
     st.end()
   })
 
-  t.test('should not write value beyond capacity', (st) => {
-    st.throws(() => m.write(30, 3, Buffer.from([1, 2, 3])), /capacity/)
-    st.end()
-  })
-
   t.test('should write value', (st) => {
     m.write(29, 3, Buffer.from([1, 2, 3]))
     st.ok(m.read(29, 5).equals(Buffer.from([1, 2, 3, 0, 0])))
@@ -40,4 +34,44 @@ tape('Memory', (t) => {
     st.throws(() => m.write(0, 5, Buffer.from([8, 8, 8])), /size/)
     st.end()
   })
+
+  t.test(
+    'should expand by word (32 bytes) properly when writing to previously untouched location',
+    (st) => {
+      const memory = new Memory()
+      memory.write(0, 1, Buffer.from([1]))
+      st.equal(memory._store.length, 32)
+
+      memory.write(1, 3, Buffer.from([2, 2, 2]))
+      st.equal(memory._store.length, 32)
+
+      memory.write(4, 32, Buffer.allocUnsafe(32).fill(3))
+      st.equal(memory._store.length, 64)
+
+      memory.write(36, 32, Buffer.allocUnsafe(32).fill(4))
+      st.equal(memory._store.length, 96)
+
+      st.end()
+    }
+  )
+
+  t.test('should expand by word (32 bytes) when reading a previously untouched location', (st) => {
+    const memory = new Memory()
+    memory.read(0, 8)
+    st.equal(memory._store.length, 32)
+
+    memory.read(1, 16)
+    st.equal(memory._store.length, 32)
+
+    memory.read(1, 32)
+    st.equal(memory._store.length, 64)
+
+    memory.read(32, 32)
+    st.equal(memory._store.length, 64)
+
+    memory.read(33, 32)
+    st.equal(memory._store.length, 96)
+
+    st.end()
+  })
 })