From abdf67ee9fa976d8248aa8f74e6a2aec8b54ee92 Mon Sep 17 00:00:00 2001
From: Hanno Becker <hanno.becker@arm.com>
Date: Fri, 26 Oct 2018 13:28:32 +0100
Subject: [PATCH] Cast number of operations to `uint` in MBEDTLS_ECP_BUDGET
Context:
The macro `MBEDTLS_ECP_BUDGET()` is called before performing a
number of potentially time-consuming ECC operations. If restartable
ECC is enabled, it wraps a call to `mbedtls_ecp_check_budget()`
which in turn checks if the requested number of operations can be
performed without exceeding the maximum number of consecutive ECC
operations.
Issue:
The function `mbedtls_ecp_check_budget()` expects a the number
of requested operations to be given as a value of type `unsigned`,
while some calls of the wrapper macro `MBEDTLS_ECP_BUDGET()` use
expressions of type `size_t`.
This rightfully leads to warnings about implicit truncation
from `size_t` to `unsigned` on some compilers.
Fix:
This commit makes the truncation explicit by adding an explicit cast
to `unsigned` in the expansion of the `MBEDTLS_ECP_BUDGET()` macro.
Justification:
Functionally, the new version is equivalent to the previous code.
The warning about truncation can be discarded because, as can be
inferred from `ecp.h`, the number of requested operations is never
larger than 1000.
---
include/mbedtls/ecp.h | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/include/mbedtls/ecp.h b/include/mbedtls/ecp.h
index 448549cfc4..5db87524e1 100644
--- a/include/mbedtls/ecp.h
+++ b/include/mbedtls/ecp.h
@@ -233,7 +233,9 @@ int mbedtls_ecp_check_budget( const mbedtls_ecp_group *grp,
unsigned ops );
/* Utility macro for checking and updating ops budget */
-#define MBEDTLS_ECP_BUDGET( ops ) MBEDTLS_MPI_CHK( mbedtls_ecp_check_budget( grp, rs_ctx, ops ) );
+#define MBEDTLS_ECP_BUDGET( ops ) \
+ MBEDTLS_MPI_CHK( mbedtls_ecp_check_budget( grp, rs_ctx, \
+ (unsigned) (ops) ) );
#else /* MBEDTLS_ECP_RESTARTABLE */