commit 628ed4e54f7ceac04cddb5abcd551f9854a8dc32
author Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com> Wed Sep 09 10:00:26 2020 +0200
committer GitHub <noreply@github.com> Wed Sep 09 10:00:26 2020 +0200
tree 9c73d5e09db081a9077813fed131f91491a576e9
parent 1ffec8f68fc1a4d7dd44c2704fc4fe3549ac927a
parent b9da1dd335f60a07c7547f16c08d6529209007ac

Merge pull request #3592 from d-otte/development

adjusting size of sliding window array to correct size.

ChangeLog.d/adjusting sliding_window_size_PR3592.txt

diff --git a/ChangeLog.d/adjusting sliding_window_size_PR3592.txt b/ChangeLog.d/adjusting sliding_window_size_PR3592.txt
new file mode 100644
index 0000000..6089565
--- /dev/null
+++ b/ChangeLog.d/adjusting sliding_window_size_PR3592.txt
@@ -0,0 +1,3 @@
+Changes
+   * Reduce stack usage significantly during sliding window exponentiation.
+     Reported in #3591 and fix contributed in #3592 by Daniel Otte.

include/mbedtls/bignum.h

diff --git a/include/mbedtls/bignum.h b/include/mbedtls/bignum.h
index 0d019b9..637360e 100644
--- a/include/mbedtls/bignum.h
+++ b/include/mbedtls/bignum.h
@@ -61,12 +61,12 @@
  * Maximum window size used for modular exponentiation. Default: 6
  * Minimum value: 1. Maximum value: 6.
  *
- * Result is an array of ( 2 << MBEDTLS_MPI_WINDOW_SIZE ) MPIs used
+ * Result is an array of ( 2 ** MBEDTLS_MPI_WINDOW_SIZE ) MPIs used
  * for the sliding window calculation. (So 64 by default)
  *
  * Reduction in size, reduces speed.
  */
-#define MBEDTLS_MPI_WINDOW_SIZE                           6        /**< Maximum windows size used. */
+#define MBEDTLS_MPI_WINDOW_SIZE                           6        /**< Maximum window size used. */
 #endif /* !MBEDTLS_MPI_WINDOW_SIZE */
 
 #if !defined(MBEDTLS_MPI_MAX_SIZE)

include/mbedtls/config.h

diff --git a/include/mbedtls/config.h b/include/mbedtls/config.h
index a2f408f..f1b834c 100644
--- a/include/mbedtls/config.h
+++ b/include/mbedtls/config.h
@@ -3461,7 +3461,7 @@
  */
 
 /* MPI / BIGNUM options */
-//#define MBEDTLS_MPI_WINDOW_SIZE            6 /**< Maximum windows size used. */
+//#define MBEDTLS_MPI_WINDOW_SIZE            6 /**< Maximum window size used. */
 //#define MBEDTLS_MPI_MAX_SIZE            1024 /**< Maximum number of bytes for usable MPIs. */
 
 /* CTR_DRBG options */

library/bignum.c

diff --git a/library/bignum.c b/library/bignum.c
index 9325632..fa97d19 100644
--- a/library/bignum.c
+++ b/library/bignum.c
@@ -2101,7 +2101,7 @@
     size_t i, j, nblimbs;
     size_t bufsize, nbits;
     mbedtls_mpi_uint ei, mm, state;
-    mbedtls_mpi RR, T, W[ 2 << MBEDTLS_MPI_WINDOW_SIZE ], Apos;
+    mbedtls_mpi RR, T, W[ 1 << MBEDTLS_MPI_WINDOW_SIZE ], Apos;
     int neg;
 
     MPI_VALIDATE_RET( X != NULL );