CBMC: Add proofs on top of native functions (poly_chknorm_native)

- This commit adds CBMC proofs for following the native function:
 `mld_poly_chknorm_native`, called `poly_chknorm_native`.

- This following changes are include:

 - Apply the same harness file and construct function contract reference
  from `poly_chknorm_native`.

 - Use the following function contracts:
  - `mld_poly_chknorm_c`
  - `mld_poly_chknorm_native`

 - Add `MLD_USE_NATIVE_POLY_CHKNORM` in dummy_backend.h

Signed-off-by: willieyz <willie.zhao@chelpis.com>

Author: willieyz

mldsa/mldsa_native.S

@@ -552,6 +552,7 @@
 #undef MLD_NATIVE_FUNC_FALLBACK
 #undef MLD_NATIVE_FUNC_SUCCESS
 #undef MLD_NTT_BOUND
+#undef REDUCE32_RANGE_MAX
 /* mldsa/src/native/meta.h */
 #undef MLD_NATIVE_META_H
 #if defined(MLD_SYS_AARCH64)

mldsa/mldsa_native.c

@@ -549,6 +549,7 @@
 #undef MLD_NATIVE_FUNC_FALLBACK
 #undef MLD_NATIVE_FUNC_SUCCESS
 #undef MLD_NTT_BOUND
+#undef REDUCE32_RANGE_MAX
 /* mldsa/src/native/meta.h */
 #undef MLD_NATIVE_META_H
 #if defined(MLD_SYS_AARCH64)

mldsa/src/native/api.h

@@ -50,6 +50,12 @@
  * in sync. */
 #define MLD_INTT_BOUND MLDSA_Q
 
+/* Absolute bound for range of mld_reduce32()
+ *
+ * NOTE: This is the same bound as in reduce.h and has to be kept
+ * in sync. */
+/* check-magic: 6283009 == (REDUCE32_DOMAIN_MAX - 255 * MLDSA_Q + 1) */
+#define REDUCE32_RANGE_MAX 6283009
 /*
  * This is the C<->native interface allowing for the drop-in of
  * native code for performance critical arithmetic components of ML-DSA.
@@ -396,7 +402,14 @@ __contract__(
  * Returns 0 if the infinity norm is strictly smaller than B, and 1
  * otherwise. B must not be larger than MLDSA_Q - REDUCE32_RANGE_MAX.
  **************************************************/
-static MLD_INLINE int mld_poly_chknorm_native(const int32_t *a, int32_t B);
+static MLD_INLINE int mld_poly_chknorm_native(const int32_t *a, int32_t B)
+__contract__(
+  requires(memory_no_alias(a, sizeof(int32_t) * MLDSA_N))
+  requires(0 <= B && B <= MLDSA_Q - REDUCE32_RANGE_MAX)
+  requires(array_bound(a, 0, MLDSA_N, -REDUCE32_RANGE_MAX, REDUCE32_RANGE_MAX))
+  ensures(return_value == MLD_NATIVE_FUNC_FALLBACK || return_value == MLD_NATIVE_FUNC_SUCCESS)
+  ensures((return_value == 0) == array_abs_bound(a, 0, MLDSA_N, B))
+);
 #endif /* MLD_USE_NATIVE_POLY_CHKNORM */
 
 #if defined(MLD_USE_NATIVE_POLYZ_UNPACK_17)

mldsa/src/poly.c

@@ -703,7 +703,6 @@ MLD_INTERNAL_API
 uint32_t mld_poly_chknorm(const mld_poly *a, int32_t B)
 {
 #if defined(MLD_USE_NATIVE_POLY_CHKNORM)
-  /* TODO: proof */
   int ret;
   int success;
   mld_assert_bound(a->coeffs, MLDSA_N, -REDUCE32_RANGE_MAX, REDUCE32_RANGE_MAX);

proofs/cbmc/dummy_backend.h

@@ -17,6 +17,7 @@
 #define MLD_USE_NATIVE_POLY_CADDQ
 #define MLD_USE_NATIVE_POLY_USE_HINT_32
 #define MLD_USE_NATIVE_POLY_USE_HINT_88
+#define MLD_USE_NATIVE_POLY_CHKNORM
 
 #include "../../mldsa/src/native/api.h"
 

proofs/cbmc/poly_chknorm_native/Makefile

@@ -0,0 +1,55 @@
+# Copyright (c) The mldsa-native project authors
+# SPDX-License-Identifier: Apache-2.0 OR ISC OR MIT
+
+include ../Makefile_params.common
+
+HARNESS_ENTRY = harness
+HARNESS_FILE =poly_chknorm_native_harness
+
+# This should be a unique identifier for this proof, and will appear on the
+# Litani dashboard. It can be human-readable and contain spaces if you wish.
+PROOF_UID = poly_chknorm_native
+
+DEFINES += -DMLD_CONFIG_USE_NATIVE_BACKEND_ARITH -DMLD_CONFIG_ARITH_BACKEND_FILE="\"dummy_backend.h\""
+INCLUDES +=
+
+REMOVE_FUNCTION_BODY +=
+UNWINDSET +=
+
+PROOF_SOURCES += $(PROOFDIR)/$(HARNESS_FILE).c
+PROJECT_SOURCES += $(SRCDIR)/mldsa/src/poly.c
+
+CHECK_FUNCTION_CONTRACTS=$(MLD_NAMESPACE)poly_chknorm
+USE_FUNCTION_CONTRACTS=mld_poly_chknorm_native mld_poly_chknorm_c
+APPLY_LOOP_CONTRACTS=on
+USE_DYNAMIC_FRAMES=1
+
+# Disable any setting of EXTERNAL_SAT_SOLVER, and choose SMT backend instead
+EXTERNAL_SAT_SOLVER=
+CBMCFLAGS=--smt2
+
+FUNCTION_NAME = poly_chknorm_native
+
+# If this proof is found to consume huge amounts of RAM, you can set the
+# EXPENSIVE variable. With new enough versions of the proof tools, this will
+# restrict the number of EXPENSIVE CBMC jobs running at once. See the
+# documentation in Makefile.common under the "Job Pools" heading for details.
+# EXPENSIVE = true
+
+# This function is large enough to need...
+CBMC_OBJECT_BITS = 8
+
+# If you require access to a file-local ("static") function or object to conduct
+# your proof, set the following (and do not include the original source file
+# ("mldsa/poly.c") in PROJECT_SOURCES).
+# REWRITTEN_SOURCES = $(PROOFDIR)/<__SOURCE_FILE_BASENAME__>.i
+# include ../Makefile.common
+# $(PROOFDIR)/<__SOURCE_FILE_BASENAME__>.i_SOURCE = $(SRCDIR)/mldsa/src/poly.c
+# $(PROOFDIR)/<__SOURCE_FILE_BASENAME__>.i_FUNCTIONS = foo bar
+# $(PROOFDIR)/<__SOURCE_FILE_BASENAME__>.i_OBJECTS = baz
+# Care is required with variables on the left-hand side: REWRITTEN_SOURCES must
+# be set before including Makefile.common, but any use of variables on the
+# left-hand side requires those variables to be defined. Hence, _SOURCE,
+# _FUNCTIONS, _OBJECTS is set after including Makefile.common.
+
+include ../Makefile.common

proofs/cbmc/poly_chknorm_native/poly_chknorm_native_harness.c

@@ -0,0 +1,13 @@
+// Copyright (c) The mldsa-native project authors
+// SPDX-License-Identifier: Apache-2.0 OR ISC OR MIT
+
+#include "poly_kl.h"
+
+
+void harness(void)
+{
+  mld_poly *a;
+  uint32_t r;
+  int32_t B;
+  r = mld_poly_chknorm(a, B);
+}