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

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Message-ID: <03183ae9-3dd3-b0da-31e6-c186b2bfcfcc@csgroup.eu>
Date:   Tue, 16 Nov 2021 14:02:32 +0100
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Sandy Harris <sandyinchina@...il.com>,
        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: Re: [PATCH 0/8] memset() in crypto code



Le 16/11/2021 à 12:20, Sandy Harris a écrit :
> 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).
> 

I see no point in doing 8 separate patches that all have the same 
subject and the exact same light description.

I think it would be better to have a single patch with all the changes, 
and use the cover letter description as description for that patch.

Christophe