commit 6dba3200d4d656635f28a28f7c8180078c8ed303
author Gilles Peskine <Gilles.Peskine@arm.com> Wed Jun 02 23:21:07 2021 +0200
committer Gilles Peskine <Gilles.Peskine@arm.com> Fri Jun 11 21:43:14 2021 +0200
tree 1f560bc66c1035aeb27b04c214ba6bf6f5a8029c
parent 863904863113737707259fe9cebbe1d241457482

Fail the build if MBEDTLS_ECP_MAX_BITS is not large enough

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

include/mbedtls/ecp.h

diff --git a/include/mbedtls/ecp.h b/include/mbedtls/ecp.h
index b974e59..a4aa3a3 100644
--- a/include/mbedtls/ecp.h
+++ b/include/mbedtls/ecp.h
@@ -171,6 +171,40 @@
 }
 mbedtls_ecp_point;
 
+/* Determine the minimum safe value of MBEDTLS_ECP_MAX_BITS. */
+#if !defined(MBEDTLS_ECP_C)
+#define MBEDTLS_ECP_MAX_BITS_MIN 0
+/* Note: the curves must be listed in DECREASING size! */
+#elif defined(MBEDTLS_ECP_DP_SECP521R1_ENABLED)
+#define MBEDTLS_ECP_MAX_BITS_MIN 521
+#elif defined(MBEDTLS_ECP_DP_BP512R1_ENABLED)
+#define MBEDTLS_ECP_MAX_BITS_MIN 512
+#elif defined(MBEDTLS_ECP_DP_CURVE448_ENABLED)
+#define MBEDTLS_ECP_MAX_BITS_MIN 448
+#elif defined(MBEDTLS_ECP_DP_BP384R1_ENABLED)
+#define MBEDTLS_ECP_MAX_BITS_MIN 384
+#elif defined(MBEDTLS_ECP_DP_SECP384R1_ENABLED)
+#define MBEDTLS_ECP_MAX_BITS_MIN 384
+#elif defined(MBEDTLS_ECP_DP_BP256R1_ENABLED)
+#define MBEDTLS_ECP_MAX_BITS_MIN 256
+#elif defined(MBEDTLS_ECP_DP_SECP256K1_ENABLED)
+#define MBEDTLS_ECP_MAX_BITS_MIN 256
+#elif defined(MBEDTLS_ECP_DP_SECP256R1_ENABLED)
+#define MBEDTLS_ECP_MAX_BITS_MIN 256
+#elif defined(MBEDTLS_ECP_DP_CURVE25519_ENABLED)
+#define MBEDTLS_ECP_MAX_BITS_MIN 255
+#elif defined(MBEDTLS_ECP_DP_SECP224K1_ENABLED)
+#define MBEDTLS_ECP_MAX_BITS_MIN 225 // n is slightly above 2^224
+#elif defined(MBEDTLS_ECP_DP_SECP224R1_ENABLED)
+#define MBEDTLS_ECP_MAX_BITS_MIN 224
+#elif defined(MBEDTLS_ECP_DP_SECP192K1_ENABLED)
+#define MBEDTLS_ECP_MAX_BITS_MIN 192
+#elif defined(MBEDTLS_ECP_DP_SECP192R1_ENABLED)
+#define MBEDTLS_ECP_MAX_BITS_MIN 192
+#else
+#error "MBEDTLS_ECP_C enabled, but no curve?"
+#endif
+
 #if !defined(MBEDTLS_ECP_ALT)
 /*
  * default mbed TLS elliptic curve arithmetic implementation
@@ -245,7 +279,13 @@
  * \{
  */
 
-#if !defined(MBEDTLS_ECP_MAX_BITS)
+#if defined(MBEDTLS_ECP_MAX_BITS)
+
+#if MBEDTLS_ECP_MAX_BITS < MBEDTLS_ECP_MAX_BITS_MIN
+#error "MBEDTLS_ECP_MAX_BITS is smaller than the largest supported curve"
+#endif
+
+#else
 /**
  * The maximum size of the groups, that is, of \c N and \c P.
  */