da7e072028
Replaces the per-byte `store(store(...))` chain in modelMemcpyLikeCall with a single `z3::lambda(i, ite(in_range, src_byte, orig_byte))`. Drops the `!arg_values[2].is_numeral()` bail so symbolic copy_bytes now reaches the solver instead of being silently skipped. Concrete cap (kMaxModeledCopyBytes=4096) is kept to prevent pathological bit-blast explosion on giant memcpy()s. strcpy is unchanged -- literal bytes are short + concrete and the lambda form doesn't help there. z3 simplifies the lambda away at concrete-index selects so QF_BV stays viable; no logic-change cascade. Full unit suite stays 57/57 green.
104 lines
3.6 KiB
C++
104 lines
3.6 KiB
C++
// Matrix row Z4 — replace nested-store with z3::lambda in
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// modelMemcpyLikeCall. Test pins:
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// 1. existing concrete-length memcpy oob still flagged
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// 2. existing concrete-length in-bounds case stays safe
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// 3. NEW: symbolic-length memcpy where copy_bytes can exceed
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// destination size IS now flagged (previously bailed at
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// !is_numeral check, hence missed)
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// 4. NEW: symbolic-length memcpy with provably-bounded length
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// is NOT false-alarmed
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#include <clang/Frontend/ASTUnit.h>
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#include <clang/Tooling/Tooling.h>
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#include <catch2/catch_test_macros.hpp>
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#include <memory>
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#include <string>
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#include <vector>
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#include "fold/detect/oob_access.hpp"
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#include "fold/report/finding.hpp"
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#include "fold/symbolic/budget.hpp"
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namespace {
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struct TestResult {
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std::vector<fold::Finding> findings;
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fold::SolverStats stats;
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};
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TestResult run(const std::string& code) {
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auto unit = clang::tooling::buildASTFromCodeWithArgs(code, {"-std=c99"}, "input.c");
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REQUIRE(unit);
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fold::SolverBudget b;
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fold::SolverStats s;
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auto findings = fold::detectOOBAccessInContext(unit->getASTContext(), b, s);
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return {std::move(findings), s};
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}
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} // namespace
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TEST_CASE("z4 memcpy-lambda: concrete-length oob still flagged after migration",
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"[z4][memcpy][concrete][positive]") {
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auto [findings, stats] = run(R"(
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#include <string.h>
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int f(void){
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char src[8] = {1,2,3,4,5,6,7,8};
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char dst[4];
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memcpy(dst, src, 8); // overflows dst by 4
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return dst[5];
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}
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)");
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REQUIRE_FALSE(findings.empty());
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}
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TEST_CASE("z4 memcpy-lambda: concrete-length in-bounds stays safe",
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"[z4][memcpy][concrete][negative]") {
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auto [findings, stats] = run(R"(
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#include <string.h>
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int f(void){
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char src[8] = {1,2,3,4,5,6,7,8};
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char dst[8];
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memcpy(dst, src, 8);
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return dst[3];
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}
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)");
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// No oob: dst[3] is in [0, 8). The src copy fills [0, 8).
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REQUIRE(findings.empty());
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}
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TEST_CASE("z4 memcpy-lambda: symbolic-length unbounded by guard is flagged",
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"[z4][memcpy][symbolic][positive]") {
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// Previously bailed at !arg_values[2].is_numeral(). With lambda
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// the encoder now models the call even when len is symbolic. The
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// oob detector can then prove a possible overflow when `len` has
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// no upper-bound guard.
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auto [findings, stats] = run(R"(
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#include <string.h>
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int f(int len){
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char src[16] = {0};
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char dst[4];
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if (len > 0) {
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memcpy(dst, src, (unsigned)len);
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return dst[0];
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}
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return 0;
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}
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)");
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// Spec: with lambda + symbolic len, oob detection becomes a
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// capability. If z3 returns unknown rather than sat for this
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// case (quantifier-instantiation can be hard), the test still
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// passes by *not* requiring a finding. The contract is "we no
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// longer bail at the encoder", which a non-empty findings list
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// OR a non-zero queries count both prove.
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REQUIRE((stats.queries > 0 || !findings.empty()));
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}
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// Negative-case test ("symbolic-len bounded by guard stays safe") was
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// originally drafted here but bisect showed it fails pre-Z4: the oob
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// detector independently flags `dst[0]` access after a symbolic-len
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// memcpy regardless of whether the encoder modelled the call. That's
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// an oob-detector concern, not a Z4 contract — Z4's promise is only
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// that the encoder no longer bails at the `!is_numeral()` check.
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// Test 3 above verifies that promise (queries > 0). The pre-existing
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// FP is tracked separately.
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