chore(avm): Handle specific MSM errors

barretenberg/cpp/src/barretenberg/vm/avm/trace/errors.hpp

@@ -24,6 +24,8 @@ enum class AvmError : uint32_t {
     OUT_OF_GAS,
     STATIC_CALL_ALTERATION,
     FAILED_BYTECODE_RETRIEVAL,
+    MSM_POINTS_LEN_INVALID,
+    MSM_POINT_NOT_ON_CURVE,
 };
 
 } // namespace bb::avm_trace

barretenberg/cpp/src/barretenberg/vm/avm/trace/helper.cpp

@@ -117,6 +117,8 @@ std::string to_name(AvmError error)
         return "TAG CHECKING ERROR";
     case AvmError::ADDR_RES_TAG_ERROR:
         return "ADDRESS RESOLUTION TAG ERROR";
+    case AvmError::MEM_SLICE_OUT_OF_RANGE:
+        return "MEMORY SLICE OUT OF RANGE";
     case AvmError::REL_ADDR_OUT_OF_RANGE:
         return "RELATIVE ADDRESS IS OUT OF RANGE";
     case AvmError::DIV_ZERO:
@@ -135,8 +137,14 @@ std::string to_name(AvmError error)
         return "SIDE EFFECT LIMIT REACHED";
     case AvmError::OUT_OF_GAS:
         return "OUT OF GAS";
+    case AvmError::STATIC_CALL_ALTERATION:
+        return "STATIC CALL ALTERATION";
     case AvmError::FAILED_BYTECODE_RETRIEVAL:
         return "FAILED BYTECODE RETRIEVAL";
+    case AvmError::MSM_POINTS_LEN_INVALID:
+        return "MSM POINTS LEN INVALID";
+    case AvmError::MSM_POINT_NOT_ON_CURVE:
+        return "MSM POINT NOT ON CURVE";
     default:
         throw std::runtime_error("Invalid error type");
         break;

barretenberg/cpp/src/barretenberg/vm/avm/trace/trace.cpp

@@ -4780,6 +4780,11 @@ AvmError AvmTraceBuilder::op_variable_msm(uint8_t indirect,
 
     const FF points_length = is_ok(error) ? unconstrained_read_from_memory(resolved_point_length_offset) : 0;
 
+    // Unconstrained check that points_length must be a multiple of 3.
+    if (is_ok(error) && static_cast<uint32_t>(points_length) % 3 != 0) {
+        error = AvmError::MSM_POINTS_LEN_INVALID;
+    }
+
     if (is_ok(error) && !check_slice_mem_range(resolved_points_offset, static_cast<uint32_t>(points_length))) {
         error = AvmError::MEM_SLICE_OUT_OF_RANGE;
     }
@@ -4863,6 +4868,10 @@ AvmError AvmTraceBuilder::op_variable_msm(uint8_t indirect,
             points.emplace_back(grumpkin::g1::affine_element::infinity());
         } else {
             points.emplace_back(x, y);
+            // Unconstrained check that this point lies on the Grumpkin curve.
+            if (!points.back().on_curve()) {
+                return AvmError::MSM_POINT_NOT_ON_CURVE;
+            }
         }
     }
     // Reconstruct Grumpkin scalars

yarn-project/simulator/src/avm/errors.ts

@@ -1,5 +1,5 @@
 import { type FailingFunction, type NoirCallStack } from '@aztec/circuit-types';
-import { type AztecAddress, type Fr } from '@aztec/circuits.js';
+import { type AztecAddress, type Fr, type Point } from '@aztec/circuits.js';
 
 import { ExecutionError } from '../common/errors.js';
 import { type AvmContext } from './avm_context.js';
@@ -128,6 +128,26 @@ export class OutOfGasError extends AvmExecutionError {
   }
 }
 
+/**
+ * Error is thrown when the supplied points length is not a multiple of 3. Specific for MSM opcode.
+ */
+export class MSMPointsLengthError extends AvmExecutionError {
+  constructor(pointsReadLength: number) {
+    super(`Points vector length should be a multiple of 3, was ${pointsReadLength}`);
+    this.name = 'MSMPointsLengthError';
+  }
+}
+
+/**
+ * Error is thrown when one of the supplied points does not lie on the Grumpkin curve. Specific for MSM opcode.
+ */
+export class MSMPointNotOnCurveError extends AvmExecutionError {
+  constructor(point: Point) {
+    super(`Point ${point.toString()} is not on the curve.`);
+    this.name = 'MSMPointNotOnCurveError';
+  }
+}
+
 /**
  * Error is thrown when a static call attempts to alter some state
  */

yarn-project/simulator/src/avm/opcodes/multi_scalar_mul.test.ts

@@ -1,8 +1,9 @@
-import { Fq, Fr } from '@aztec/circuits.js';
+import { Fq, Fr, Point } from '@aztec/circuits.js';
 import { Grumpkin } from '@aztec/circuits.js/barretenberg';
 
 import { type AvmContext } from '../avm_context.js';
 import { Field, type MemoryValue, Uint1, Uint32 } from '../avm_memory_types.js';
+import { MSMPointNotOnCurveError, MSMPointsLengthError } from '../errors.js';
 import { initContext } from '../fixtures/index.js';
 import { MultiScalarMul } from './multi_scalar_mul.js';
 
@@ -127,4 +128,54 @@ describe('MultiScalarMul Opcode', () => {
 
     expect(result).toEqual([expectedResult.x, expectedResult.y, new Fr(0n)]);
   });
+
+  it('Should throw an error if points length is not a multiple of 3', async () => {
+    const indirect = 0;
+
+    // No need to set up points nor scalars as it is expected to fail before any processing of them.
+    const pointsReadLength = 17; // Not multiple of 3
+    const pointsOffset = 0;
+    const scalarsOffset = 20;
+    const pointsLengthOffset = 100;
+    const outputOffset = 120;
+
+    context.machineState.memory.set(pointsLengthOffset, new Uint32(pointsReadLength));
+
+    await expect(
+      new MultiScalarMul(indirect, pointsOffset, scalarsOffset, outputOffset, pointsLengthOffset).execute(context),
+    ).rejects.toThrow(MSMPointsLengthError);
+  });
+
+  it('Should throw an error if a point is not on Grumpkin curve', async () => {
+    const indirect = 0;
+    const grumpkin = new Grumpkin();
+    // We need to ensure points are actually on curve, so we just use the generator
+    // In future we could use a random point, for now we create an array of [G, 2G, NOT_ON_CURVE]
+    const points = Array.from({ length: 2 }, (_, i) => grumpkin.mul(grumpkin.generator(), new Fq(i + 1)));
+    points.push(new Point(new Fr(13), new Fr(14), false));
+
+    const scalars = [new Fq(5n), new Fq(3n), new Fq(1n)];
+    const pointsReadLength = points.length * 3; // multiplied by 3 since we will store them as triplet in avm memory
+    const scalarsLength = scalars.length * 2; // multiplied by 2 since we will store them as lo and hi limbs in avm memory
+    // Transform the points and scalars into the format that we will write to memory
+    // We just store the x and y coordinates here, and handle the infinities when we write to memory
+    const storedScalars: Field[] = scalars.flatMap(s => [new Field(s.lo), new Field(s.hi)]);
+    // Points are stored as [x1, y1, inf1, x2, y2, inf2, ...] where the types are [Field, Field, Uint8, Field, Field, Uint8, ...]
+    const storedPoints: MemoryValue[] = points
+      .map(p => p.toFields())
+      .flatMap(([x, y, inf]) => [new Field(x), new Field(y), new Uint1(inf.toNumber())]);
+    const pointsOffset = 0;
+    context.machineState.memory.setSlice(pointsOffset, storedPoints);
+    // Store scalars
+    const scalarsOffset = pointsOffset + pointsReadLength;
+    context.machineState.memory.setSlice(scalarsOffset, storedScalars);
+    // Store length of points to read
+    const pointsLengthOffset = scalarsOffset + scalarsLength;
+    context.machineState.memory.set(pointsLengthOffset, new Uint32(pointsReadLength));
+    const outputOffset = pointsLengthOffset + 1;
+
+    await expect(
+      new MultiScalarMul(indirect, pointsOffset, scalarsOffset, outputOffset, pointsLengthOffset).execute(context),
+    ).rejects.toThrow(MSMPointNotOnCurveError);
+  });
 });

yarn-project/simulator/src/avm/opcodes/multi_scalar_mul.ts

@@ -3,7 +3,7 @@ import { Grumpkin } from '@aztec/circuits.js/barretenberg';
 
 import { type AvmContext } from '../avm_context.js';
 import { Field, TypeTag, Uint1 } from '../avm_memory_types.js';
-import { InstructionExecutionError } from '../errors.js';
+import { MSMPointNotOnCurveError, MSMPointsLengthError } from '../errors.js';
 import { Opcode, OperandType } from '../serialization/instruction_serialization.js';
 import { Addressing } from './addressing_mode.js';
 import { Instruction } from './instruction.js';
@@ -44,7 +44,7 @@ export class MultiScalarMul extends Instruction {
     // Get the size of the unrolled (x, y , inf) points vector
     const pointsReadLength = memory.get(pointsLengthOffset).toNumber();
     if (pointsReadLength % 3 !== 0) {
-      throw new InstructionExecutionError(`Points vector offset should be a multiple of 3, was ${pointsReadLength}`);
+      throw new MSMPointsLengthError(pointsReadLength);
     }
 
     // Get the unrolled (x, y, inf) representing the points
@@ -76,7 +76,7 @@ export class MultiScalarMul extends Instruction {
       const isInf = pointsVector[3 * i + 2].toNumber() === 1;
       const p: Point = new Point(pointsVector[3 * i].toFr(), pointsVector[3 * i + 1].toFr(), isInf);
       if (!p.isOnGrumpkin()) {
-        throw new InstructionExecutionError(`Point ${p.toString()} is not on the curve.`);
+        throw new MSMPointNotOnCurveError(p);
       }
       grumpkinPoints.push(p);
     }