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

- This commit adds CBMC proofs for following the native function:
 `mld_polyz_unpack_17_native` and `mld_polyz_unpack_19_native`.
 called `polyz_unpack_native`.

- This following changes are include:

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

 - Use the following function contracts:
   - `mld_polyz_unpack_c`
   - `mld_polyz_unpack_17_native`
   - `mld_polyz_unpack_17_native`

 - Add `MLD_USE_NATIVE_POLYZ_UNPACK_17`,
  `MLD_USE_NATIVE_POLYZ_UNPACK_19` in dummy_backend.h

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

Author: willieyz

mldsa/src/native/api.h

@@ -423,7 +423,15 @@ __contract__(
  * Arguments:   - int32_t *r: pointer to output polynomial
  *              - const uint8_t *a: byte array with bit-packed polynomial
  **************************************************/
-static MLD_INLINE int mld_polyz_unpack_17_native(int32_t *r, const uint8_t *a);
+static MLD_INLINE int mld_polyz_unpack_17_native(int32_t *r, const uint8_t *a)
+__contract__(
+  requires(memory_no_alias(r, sizeof(int32_t) * MLDSA_N))
+  requires(memory_no_alias(a, MLDSA_POLYZ_PACKEDBYTES))
+  assigns(memory_slice(r, sizeof(int32_t) * MLDSA_N))
+  ensures(return_value == MLD_NATIVE_FUNC_FALLBACK || return_value == MLD_NATIVE_FUNC_SUCCESS)
+  ensures((return_value == MLD_NATIVE_FUNC_SUCCESS) ==> array_bound(r, 0, MLDSA_N, -(MLDSA_GAMMA1 - 1), MLDSA_GAMMA1 + 1))
+  ensures((return_value == MLD_NATIVE_FUNC_FALLBACK) ==> array_unchanged(r, MLDSA_N))
+);
 #endif /* MLD_USE_NATIVE_POLYZ_UNPACK_17 */
 
 #if defined(MLD_USE_NATIVE_POLYZ_UNPACK_19)
@@ -437,7 +445,15 @@ static MLD_INLINE int mld_polyz_unpack_17_native(int32_t *r, const uint8_t *a);
  * Arguments:   - int32_t *r: pointer to output polynomial
  *              - const uint8_t *a: byte array with bit-packed polynomial
  **************************************************/
-static MLD_INLINE int mld_polyz_unpack_19_native(int32_t *r, const uint8_t *a);
+static MLD_INLINE int mld_polyz_unpack_19_native(int32_t *r, const uint8_t *a)
+__contract__(
+  requires(memory_no_alias(r, sizeof(int32_t) * MLDSA_N))
+  requires(memory_no_alias(a, MLDSA_POLYZ_PACKEDBYTES))
+  assigns(memory_slice(r, sizeof(int32_t) * MLDSA_N))
+  ensures(return_value == MLD_NATIVE_FUNC_FALLBACK || return_value == MLD_NATIVE_FUNC_SUCCESS)
+  ensures((return_value == MLD_NATIVE_FUNC_SUCCESS) ==> array_bound(r, 0, MLDSA_N, -(MLDSA_GAMMA1 - 1), MLDSA_GAMMA1 + 1))
+  ensures((return_value == MLD_NATIVE_FUNC_FALLBACK) ==> array_unchanged(r, MLDSA_N))
+);
 #endif /* MLD_USE_NATIVE_POLYZ_UNPACK_19 */
 
 #if defined(MLD_USE_NATIVE_POINTWISE_MONTGOMERY)

mldsa/src/poly_kl.c

@@ -861,7 +861,6 @@ MLD_INTERNAL_API
 void mld_polyz_unpack(mld_poly *r, const uint8_t a[MLDSA_POLYZ_PACKEDBYTES])
 {
 #if defined(MLD_USE_NATIVE_POLYZ_UNPACK_17) && MLD_CONFIG_PARAMETER_SET == 44
-  /* TODO: proof */
   int ret;
   ret = mld_polyz_unpack_17_native(r->coeffs, a);
   if (ret == MLD_NATIVE_FUNC_SUCCESS)
@@ -871,7 +870,6 @@ void mld_polyz_unpack(mld_poly *r, const uint8_t a[MLDSA_POLYZ_PACKEDBYTES])
   }
 #elif defined(MLD_USE_NATIVE_POLYZ_UNPACK_19) && \
     (MLD_CONFIG_PARAMETER_SET == 65 || MLD_CONFIG_PARAMETER_SET == 87)
-  /* TODO: proof */
   int ret;
   ret = mld_polyz_unpack_19_native(r->coeffs, a);
   if (ret == MLD_NATIVE_FUNC_SUCCESS)

proofs/cbmc/dummy_backend.h

@@ -18,6 +18,8 @@
 #define MLD_USE_NATIVE_POLY_USE_HINT_32
 #define MLD_USE_NATIVE_POLY_USE_HINT_88
 #define MLD_USE_NATIVE_POLY_CHKNORM
+#define MLD_USE_NATIVE_POLYZ_UNPACK_17
+#define MLD_USE_NATIVE_POLYZ_UNPACK_19
 
 #include "../../mldsa/src/native/api.h"
 

proofs/cbmc/polyz_unpack_native/Makefile

@@ -0,0 +1,62 @@
+# 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 = polyz_unpack_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 = polyz_unpack_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 += $(SRCDIR)/mldsa/src/poly_kl.c
+
+CHECK_FUNCTION_CONTRACTS=$(MLD_NAMESPACE)polyz_unpack
+USE_FUNCTION_CONTRACTS=mld_polyz_unpack_c
+ifeq ($(MLD_CONFIG_PARAMETER_SET),44)
+	USE_FUNCTION_CONTRACTS+=mld_polyz_unpack_17_native
+else ifeq ($(MLD_CONFIG_PARAMETER_SET),65)
+	USE_FUNCTION_CONTRACTS+=mld_polyz_unpack_19_native
+else ifeq ($(MLD_CONFIG_PARAMETER_SET),87)
+	USE_FUNCTION_CONTRACTS+=mld_polyz_unpack_19_native
+endif
+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 = polyz_unpack_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/polyz_unpack_native/polyz_unpack_native_harness.c

@@ -0,0 +1,11 @@
+// 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;
+  uint8_t *b;
+  mld_polyz_unpack(a, b);
+}