C++: Don't consider additional loads when reusing dataflow operands.

Author: MathiasVP

cpp/ql/lib/semmle/code/cpp/ir/dataflow/internal/DataFlowPrivate.qll

@@ -692,7 +692,7 @@ predicate storeStep(Node node1, ContentSet c, Node node2) { storeStepImpl(node1,
 private predicate numberOfLoadsFromOperandRec(
   Operand operandFrom, Operand operandTo, int ind, boolean certain
 ) {
-  exists(Instruction load | Ssa::isDereference(load, operandFrom) |
+  exists(Instruction load | Ssa::isDereference(load, operandFrom, _) |
     operandTo = operandFrom and ind = 0 and certain = true
     or
     numberOfLoadsFromOperand(load.getAUse(), operandTo, ind - 1, certain)
@@ -716,7 +716,7 @@ private predicate numberOfLoadsFromOperand(
 ) {
   numberOfLoadsFromOperandRec(operandFrom, operandTo, n, certain)
   or
-  not Ssa::isDereference(_, operandFrom) and
+  not Ssa::isDereference(_, operandFrom, _) and
   not conversionFlow(operandFrom, _, _, _) and
   operandFrom = operandTo and
   n = 0 and

cpp/ql/lib/semmle/code/cpp/ir/dataflow/internal/SsaInternals.qll

@@ -610,7 +610,7 @@ private predicate indirectConversionFlowStep(Node nFrom, Node nTo) {
       hasOperandAndIndex(nFrom, op1, pragma[only_bind_into](indirectionIndex)) and
       hasOperandAndIndex(nTo, op2, indirectionIndex - 1) and
       instr = op2.getDef() and
-      isDereference(instr, op1)
+      isDereference(instr, op1, _)
     )
   )
 }

cpp/ql/lib/semmle/code/cpp/ir/dataflow/internal/SsaInternalsCommon.qll

@@ -320,10 +320,12 @@ private module IteratorIndirections {
   }
 }
 
-predicate isDereference(Instruction deref, Operand address) {
-  any(Indirection ind).isAdditionalDereference(deref, address)
+predicate isDereference(Instruction deref, Operand address, boolean additional) {
+  any(Indirection ind).isAdditionalDereference(deref, address) and
+  additional = true
   or
-  deref.(LoadInstruction).getSourceAddressOperand() = address
+  deref.(LoadInstruction).getSourceAddressOperand() = address and
+  additional = false
 }
 
 predicate isWrite(Node0Impl value, Operand address, boolean certain) {
@@ -545,7 +547,7 @@ private module Cached {
       isDef(_, value, iteratorDerefAddress, iteratorBase, numberOfLoads + 2, 0) and
       isUse(_, iteratorAddress, iteratorBase, numberOfLoads + 1, 0) and
       iteratorBase.getResultType() instanceof Interfaces::Iterator and
-      isDereference(iteratorAddress.getDef(), read.getArgumentDef().getAUse()) and
+      isDereference(iteratorAddress.getDef(), read.getArgumentDef().getAUse(), _) and
       memory = read.getSideEffectOperand().getAnyDef()
     )
   }
@@ -786,7 +788,7 @@ private module Cached {
   ) {
     indirectionIndex = [1 .. countIndirectionsForCppType(getLanguageType(operand))] and
     exists(Instruction load |
-      isDereference(load, operand) and
+      isDereference(load, operand, false) and
       operandRepr = unique( | | getAUse(load)) and
       indirectionIndexRepr = indirectionIndex - 1
     )
@@ -806,7 +808,7 @@ private module Cached {
     indirectionIndex = [1 .. countIndirectionsForCppType(getResultLanguageType(instr))] and
     exists(Instruction load, Operand address |
       address.getDef() = instr and
-      isDereference(load, address) and
+      isDereference(load, address, false) and
       instrRepr = load and
       indirectionIndexRepr = indirectionIndex - 1
     )
@@ -829,7 +831,7 @@ private module Cached {
     or
     exists(int ind0 |
       exists(Operand address |
-        isDereference(operand.getDef(), address) and
+        isDereference(operand.getDef(), address, _) and
         isUseImpl(address, base, ind0)
       )
       or
@@ -899,7 +901,7 @@ private module Cached {
     )
     or
     exists(Operand address, boolean certain0 |
-      isDereference(operand.getDef(), address) and
+      isDereference(operand.getDef(), address, _) and
       isDefImpl(address, base, ind - 1, certain0)
     |
       if isCertainAddress(operand) then certain = certain0 else certain = false

cpp/ql/lib/semmle/code/cpp/ir/dataflow/internal/TaintTrackingUtil.qll

@@ -57,7 +57,7 @@ private predicate operandToInstructionTaintStep(Operand opFrom, Instruction inst
   )
   or
   // Taint flow from an address to its dereference.
-  Ssa::isDereference(instrTo, opFrom)
+  Ssa::isDereference(instrTo, opFrom, _)
   or
   // Unary instructions tend to preserve enough information in practice that we
   // want taint to flow through.

cpp/ql/test/library-tests/dataflow/taint-tests/taint.expected

@@ -4,5 +4,4 @@ WARNING: Module DataFlow has been deprecated and may be removed in future (taint
 WARNING: Module DataFlow has been deprecated and may be removed in future (taint.ql:68,25-33)
 WARNING: Module TaintTracking has been deprecated and may be removed in future (taint.ql:73,20-33)
 testFailures
-| vector.cpp:532:10:532:12 | call to operator[] | Unexpected result: ir= |
 failures