linux-kernel - [PATCH 0/8] memset() in crypto code

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Date:   Tue, 16 Nov 2021 19:20:02 +0800
From:   Sandy Harris <sandyinchina@...il.com>
To:     LKML <linux-kernel@...r.kernel.org>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 0/8] memset() in crypto code

Fairly often we want to clear some memory in crypto code; it holds
things we are done using and do not want to leave lying around where
an enemy might discover them. Typical examples are crypto keys or
random numbers we have generated and used for output.

The obvious way to do this is with memset(address,0,bytes) but there
is a problem with that; because we are done using that memory, the
compiler may optimise away the "useless" memset() call. Using
memzero_explicit(address,bytes) instead solves the problem; that
function is designed to resist the optimisation.

There are well over 100 memset() calls in .c files in the crypto and
security directories. I looked at them all and found about a dozen in
eight files that I thought should be changed to memzero_explicit().
Here they are as patches 1 to 8 in this series.

I did read some code & think moderately carefully, but I do not know
the code deeply & it is possible I have made some errors. I think
false positives (making unnecessary changes) are more likely than
false negatives (not catching necessary changes).