cpp: Add 'cpp/mmio-unsanitized-memcpy' query

geoffw0 · Sep 18, 2026 · Aug 27, 2026 · Aug 31, 2026 · Sep 2, 2026 · Sep 3, 2026
commit b681bc4eb222b6fbd6a157b45ae0121588654bde
diff --git a/cpp/ql/src/Security/CWE/CWE-120/MmioUnsanitizedMemcpy.qhelp b/cpp/ql/src/Security/CWE/CWE-120/MmioUnsanitizedMemcpy.qhelp
@@ -0,0 +1,35 @@
+<!DOCTYPE qhelp PUBLIC
+  "-//Semmle//qhelp//EN"
+  "qhelp.dtd">
+<qhelp>
+<overview>
+<p>
+Firmware and embedded drivers often copy data into buffers using lengths read from
+memory-mapped I/O (MMIO) registers or DMA descriptor fields. When those lengths are not
+validated against the destination buffer size, an attacker who can influence hardware
+registers or DMA metadata can trigger buffer overflows and potentially achieve remote
+code execution on microcontrollers, WiFi stacks, and cellular basebands.
+</p>
+</overview>
+<recommendation>
+<p>
+Always validate MMIO/DMA-derived lengths before passing them to <code>memcpy</code>,
+<code>memmove</code>, or <code>strncpy</code>. Compare against a compile-time maximum
+and reject or clamp out-of-range values before copying.
+</p>
+</recommendation>
+<example>
+<p>Bad: length from an MMIO register used directly as the copy size.</p>
+<sample src="MmioUnsanitizedMemcpyBad.c" />
+<p>Good: defensive bounds check before the copy.</p>
+<sample src="MmioUnsanitizedMemcpyGood.c" />
+</example>
+<references>
+<li>
+CWE-120: Buffer Copy without Checking Size of Input
+</li>
+<li>
+CWE-787: Out-of-bounds Write
+</li>
+</references>
+</qhelp>
diff --git a/cpp/ql/src/Security/CWE/CWE-120/MmioUnsanitizedMemcpy.ql b/cpp/ql/src/Security/CWE/CWE-120/MmioUnsanitizedMemcpy.ql
@@ -0,0 +1,84 @@
+/**
+ * @name MMIO/DMA unsanitized memory copy
+ * @description Memory copy sizes derived from memory-mapped I/O or DMA
+ *              descriptor fields without bounds validation may overflow
+ *              destination buffers.
+ * @kind path-problem
+ * @problem.severity error
+ * @security-severity 8.6
+ * @precision medium
+ * @id cpp/mmio-unsanitized-memcpy
+ * @tags security
+ *       external/cwe/cwe-120
+ *       external/cwe/cwe-787
+ */
+
+import cpp
+import semmle.code.cpp.dataflow.new.TaintTracking
+import semmle.code.cpp.controlflow.IRGuards
+import MmioFlow::PathGraph
+
+/** Holds if `e` is an expression that reads MMIO/DMA hardware state. */
+predicate isMmioExpr(Expr e) {
+  exists(VariableAccess va | va = e and va.getTarget().isVolatile())
+  or
+  exists(FieldAccess fa | fa = e and fa.getTarget().getType().isVolatile())
+  or
+  exists(FunctionCall call |
+    call = e and
+    call.getTarget().hasName(["READ_REG", "GET_MMIO", "REG_READ", "DMA_READ"])
+  )
+  or
+  exists(PointerDereferenceExpr deref |
+    deref = e and
+    deref.getOperand().getUnspecifiedType() instanceof PointerType and
+    deref.getOperand().getUnspecifiedType().(PointerType).getBaseType().isVolatile()
+  )
+}
+
+predicate isMmioSource(DataFlow::Node source) {
+  isMmioExpr(source.asExpr())
+  or
+  exists(MacroInvocation mi |
+    mi.getMacro().hasName(["READ_REG", "GET_MMIO", "REG_READ", "DMA_READ"]) and
+    source.asExpr() = mi.getExpr()
+  )
+}
+
+predicate isMemcpySizeSink(DataFlow::Node sink, FunctionCall fc) {
+  fc.getTarget().hasName(["memcpy", "memmove", "strncpy", "wmemcpy", "wmemmove"]) and
+  sink.asExpr() = fc.getArgument(2)
+}
+
+/** Recognizes relational comparison bounds checks using public IRGuards API. */
+predicate lessThanOrEqual(IRGuardCondition g, Expr e, boolean branch) {
+  exists(Operand left |
+    g.comparesLt(left, _, _, true, branch) or
+    g.comparesEq(left, _, _, true, branch)
+  |
+    left.getDef().getConvertedResultExpression() = e
+  )
+}
+
+module MmioConfig implements DataFlow::ConfigSig {
+  predicate isSource(DataFlow::Node source) { isMmioSource(source) }
+
+  predicate isSink(DataFlow::Node sink) { isMemcpySizeSink(sink, _) }
+
+  predicate isBarrier(DataFlow::Node node) {
+    node = DataFlow::BarrierGuard<lessThanOrEqual/3>::getABarrierNode() or
+    node = DataFlow::BarrierGuard<lessThanOrEqual/3>::getAnIndirectBarrierNode()
+  }
+
+  predicate observeDiffInformedIncrementalMode() { any() }
+}
+
+module MmioFlow = TaintTracking::Global<MmioConfig>;
+
+from FunctionCall memcpyCall, MmioFlow::PathNode source, MmioFlow::PathNode sink
+where
+  MmioFlow::flowPath(source, sink) and
+  isMemcpySizeSink(sink.getNode(), memcpyCall)
+select memcpyCall, source, sink,
+  "Memory copy size argument is derived from $@ without sufficient bounds validation.",
+  source.getNode(), "an MMIO/DMA hardware register read"
diff --git a/cpp/ql/src/Security/CWE/CWE-120/MmioUnsanitizedMemcpyBad.c b/cpp/ql/src/Security/CWE/CWE-120/MmioUnsanitizedMemcpyBad.c
@@ -0,0 +1,9 @@
+#define READ_REG(addr) (*(volatile unsigned int *)(addr))
+#define MAX_DMA_LEN 64
+
+void *memcpy(void *dest, const void *src, unsigned long n);
+
+void bad_mmio_memcpy(char *dst, char *src) {
+  unsigned int len = READ_REG(0x40001000);
+  memcpy(dst, src, len);
+}
diff --git a/cpp/ql/src/Security/CWE/CWE-120/MmioUnsanitizedMemcpyGood.c b/cpp/ql/src/Security/CWE/CWE-120/MmioUnsanitizedMemcpyGood.c
@@ -0,0 +1,10 @@
+#define READ_REG(addr) (*(volatile unsigned int *)(addr))
+#define MAX_DMA_LEN 64
+
+void *memcpy(void *dest, const void *src, unsigned long n);
+
+void good_mmio_memcpy(char *dst, char *src) {
+  unsigned int len = READ_REG(0x40001000);
+  if (len <= MAX_DMA_LEN)
+    memcpy(dst, src, len);
+}
diff --git a/cpp/ql/src/codeql-suites/cpp-security-extended.qls b/cpp/ql/src/codeql-suites/cpp-security-extended.qls
@@ -3,3 +3,6 @@
 - apply: security-extended-selectors.yml
   from: codeql/suite-helpers
 - apply: codeql-suites/exclude-slow-queries.yml
+# CWE-120: MMIO/DMA unsanitized memcpy (also selected by metadata; explicit for review)
+- include:
+    id: cpp/mmio-unsanitized-memcpy
diff --git a/...est/query-tests/Security/CWE/CWE-120/MmioUnsanitizedMemcpy/MmioUnsanitizedMemcpy.expected b/...est/query-tests/Security/CWE/CWE-120/MmioUnsanitizedMemcpy/MmioUnsanitizedMemcpy.expected
@@ -0,0 +1,22 @@
+#select
+| test.c:21:3:21:8 | call to memcpy | test.c:20:18:20:37 | * ... | test.c:21:20:21:22 | len | Memory copy size argument is derived from $@ without sufficient bounds validation. | test.c:20:18:20:37 | * ... | an MMIO/DMA hardware register read |
+| test.c:26:3:26:9 | call to memmove | test.c:25:18:25:25 | call to GET_MMIO | test.c:26:21:26:23 | len | Memory copy size argument is derived from $@ without sufficient bounds validation. | test.c:25:18:25:25 | call to GET_MMIO | an MMIO/DMA hardware register read |
+| test.c:31:3:31:9 | call to strncpy | test.c:30:18:30:29 | mmio_len_reg | test.c:31:21:31:23 | len | Memory copy size argument is derived from $@ without sufficient bounds validation. | test.c:30:18:30:29 | mmio_len_reg | an MMIO/DMA hardware register read |
+edges
+| test.c:20:18:20:37 | * ... | test.c:20:18:20:37 | * ... | provenance |  |
+| test.c:20:18:20:37 | * ... | test.c:21:20:21:22 | len | provenance |  |
+| test.c:25:18:25:25 | call to GET_MMIO | test.c:25:18:25:25 | call to GET_MMIO | provenance |  |
+| test.c:25:18:25:25 | call to GET_MMIO | test.c:26:21:26:23 | len | provenance |  |
+| test.c:30:18:30:29 | mmio_len_reg | test.c:30:18:30:29 | mmio_len_reg | provenance |  |
+| test.c:30:18:30:29 | mmio_len_reg | test.c:31:21:31:23 | len | provenance |  |
+nodes
+| test.c:20:18:20:37 | * ... | semmle.label | * ... |
+| test.c:20:18:20:37 | * ... | semmle.label | * ... |
+| test.c:21:20:21:22 | len | semmle.label | len |
+| test.c:25:18:25:25 | call to GET_MMIO | semmle.label | call to GET_MMIO |
+| test.c:25:18:25:25 | call to GET_MMIO | semmle.label | call to GET_MMIO |
+| test.c:26:21:26:23 | len | semmle.label | len |
+| test.c:30:18:30:29 | mmio_len_reg | semmle.label | mmio_len_reg |
+| test.c:30:18:30:29 | mmio_len_reg | semmle.label | mmio_len_reg |
+| test.c:31:21:31:23 | len | semmle.label | len |
+subpaths
diff --git a/...l/test/query-tests/Security/CWE/CWE-120/MmioUnsanitizedMemcpy/MmioUnsanitizedMemcpy.qlref b/...l/test/query-tests/Security/CWE/CWE-120/MmioUnsanitizedMemcpy/MmioUnsanitizedMemcpy.qlref
@@ -0,0 +1,2 @@
+query: Security/CWE/CWE-120/MmioUnsanitizedMemcpy.ql
+postprocess: utils/test/InlineExpectationsTestQuery.ql
diff --git a/cpp/ql/test/query-tests/Security/CWE/CWE-120/MmioUnsanitizedMemcpy/test.c b/cpp/ql/test/query-tests/Security/CWE/CWE-120/MmioUnsanitizedMemcpy/test.c
@@ -0,0 +1,50 @@
+/* Semmle test case for MmioUnsanitizedMemcpy.ql
+ * MMIO/DMA register reads flowing into memcpy/memmove/strncpy size parameters.
+ */
+
+typedef unsigned int uint32_t;
+
+void *memcpy(void *dest, const void *src, unsigned long n);
+void *memmove(void *dest, const void *src, unsigned long n);
+char *strncpy(char *dest, const char *src, unsigned long n);
+
+#define READ_REG(addr) (*(volatile uint32_t *)(addr))
+#define MAX_DMA_LEN 64
+
+uint32_t GET_MMIO(unsigned long addr);
+uint32_t DMA_READ(unsigned long addr);
+
+volatile uint32_t mmio_len_reg;
+
+static void bad_read_reg(char *dst, char *src) {
+  uint32_t len = READ_REG(0x40001000); // $ Source
+  memcpy(dst, src, len); // $ Alert
+}
+
+static void bad_get_mmio(char *dst, char *src) {
+  uint32_t len = GET_MMIO(0x50000000); // $ Source
+  memmove(dst, src, len); // $ Alert
+}
+
+static void bad_volatile_global(char *dst, char *src) {
+  uint32_t len = mmio_len_reg; // $ Source
+  strncpy(dst, src, len); // $ Alert
+}
+
+static void good_bounded(char *dst, char *src) {
+  uint32_t len = READ_REG(0x40001000);
+  if (len <= MAX_DMA_LEN)
+    memcpy(dst, src, len); // GOOD
+}
+
+static void good_early_return(char *dst, char *src) {
+  uint32_t len = DMA_READ(0x60000000);
+  if (len > MAX_DMA_LEN)
+    return;
+  memcpy(dst, src, len); // GOOD
+}
+
+static void good_constant_size(char *dst, char *src) {
+  uint32_t len = READ_REG(0x40001000);
+  memcpy(dst, src, 32); // GOOD — constant size, not tainted sink
+}
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,2 @@
		query: Security/CWE/CWE-120/MmioUnsanitizedMemcpy.ql
		postprocess: utils/test/InlineExpectationsTestQuery.ql