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C++: Also handle reverse flow on instructions in dataflow #14384

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Merged
MathiasVP merged 1 commit into from
Oct 5, 2023
Merged

C++: Also handle reverse flow on instructions in dataflow #14384

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44 changes: 34 additions & 10 deletions cpp/ql/lib/semmle/code/cpp/ir/dataflow/internal/DataFlowUtil.qll
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Original file line number Diff line number Diff line change
Expand Up @@ -1696,16 +1696,7 @@ private module Cached {
// Reverse flow: data that flows from the definition node back into the indirection returned
// by a function. This allows data to flow 'in' through references returned by a modeled
// function such as `operator[]`.
exists(Operand address, int indirectionIndex |
nodeHasOperand(nodeTo.(IndirectReturnOutNode), address, indirectionIndex)
|
exists(StoreInstruction store |
nodeHasInstruction(nodeFrom, store, indirectionIndex - 1) and
store.getDestinationAddressOperand() = address
)
or
Ssa::outNodeHasAddressAndIndex(nodeFrom, address, indirectionIndex)
)
reverseFlow(nodeFrom, nodeTo)
}

private predicate simpleInstructionLocalFlowStep(Operand opFrom, Instruction iTo) {
Expand Down Expand Up @@ -1736,6 +1727,39 @@ private module Cached {
)
)
}

private predicate reverseFlow(Node nodeFrom, Node nodeTo) {
reverseFlowOperand(nodeFrom, nodeTo)
or
reverseFlowInstruction(nodeFrom, nodeTo)
}

private predicate reverseFlowOperand(Node nodeFrom, IndirectReturnOutNode nodeTo) {
exists(Operand address, int indirectionIndex |
nodeHasOperand(nodeTo, address, indirectionIndex)
|
exists(StoreInstruction store |
nodeHasInstruction(nodeFrom, store, indirectionIndex - 1) and
store.getDestinationAddressOperand() = address
)
or
// We also want a write coming out of an `OutNode` to flow `nodeTo`.
// This is different from `reverseFlowInstruction` since `nodeFrom` can never
// be an `OutNode` when it's defined by an instruction.
Ssa::outNodeHasAddressAndIndex(nodeFrom, address, indirectionIndex)
)
}

private predicate reverseFlowInstruction(Node nodeFrom, IndirectReturnOutNode nodeTo) {
exists(Instruction address, int indirectionIndex |
nodeHasInstruction(nodeTo, address, indirectionIndex)
|
exists(StoreInstruction store |
nodeHasInstruction(nodeFrom, store, indirectionIndex - 1) and
store.getDestinationAddress() = address
)
)
}
}

import Cached
Expand Down