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bn/bn_exp.c: explain 'volatile' in MOD_EXP_CTIME_COPY_FROM_PREBUF.

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Reviewed-by: Tim Hudson <tjh@openssl.org>
This commit is contained in:
Andy Polyakov 2016-05-26 21:40:09 +02:00
parent dae9e15d74
commit bb83c8796b
1 changed files with 8 additions and 0 deletions
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8
crypto/bn/bn_exp.c
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@ -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)