From bb83c8796b9e708a881f7c49a2af7921e73b2298 Mon Sep 17 00:00:00 2001 From: Andy Polyakov Date: Thu, 26 May 2016 21:40:09 +0200 Subject: [PATCH] bn/bn_exp.c: explain 'volatile' in MOD_EXP_CTIME_COPY_FROM_PREBUF. Reviewed-by: Tim Hudson --- crypto/bn/bn_exp.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/crypto/bn/bn_exp.c b/crypto/bn/bn_exp.c index 25c05fadba..d334cf705b 100644 --- a/crypto/bn/bn_exp.c +++ b/crypto/bn/bn_exp.c @@ -527,6 +527,14 @@ static int MOD_EXP_CTIME_COPY_FROM_PREBUF(BIGNUM *b, int top, { int i, j; int width = 1 << window; + /* + * We declare table 'volatile' in order to discourage compiler + * from reordering loads from the table. Concern is that if + * reordered in specific manner loads might give away the + * information we are trying to conceal. Some would argue that + * compiler can reorder them anyway, but it can as well be + * argued that doing so would be violation of standard... + */ volatile BN_ULONG *table = (volatile BN_ULONG *)buf; if (bn_wexpand(b, top) == NULL) -- 2.25.1