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From: Herbert Xu <herbert-lOAM2aK0SrRLBo1qDEOMRrpzq4S04n8Q@public.gmane.org>
To: Giel van Schijndel <me-sZ9Uef1cvPWHXe+LvDLADg@public.gmane.org>
Cc: linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	"David S. Miller" <davem-fT/PcQaiUtIeIZ0/mPfg9Q@public.gmane.org>,
	Thomas Gleixner <tglx-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org>,
	Ingo Molnar <mingo-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
	"H. Peter Anvin" <hpa-YMNOUZJC4hwAvxtiuMwx3w@public.gmane.org>,
	"maintainer:X86 ARCHITECTURE..."
	<x86-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
	Greg Kroah-Hartman
	<gregkh-hQyY1W1yCW8ekmWlsbkhG0B+6BGkLq7r@public.gmane.org>,
	Steve French <sfrench-eUNUBHrolfbYtjvyW6yDsg@public.gmane.org>,
	Rahul Bedarkar
	<rahulbedarkar89-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
	Thomas Pugliese
	<thomas.pugliese-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
	Randy Dunlap <rdunlap-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>,
	Julia Lawall <Julia.Lawall-L2FTfq7BK8M@public.gmane.org>,
	"open list:CRYPTO API"
	<linux-crypto-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	"open list:CERTIFIED WIRELES..."
	<linux-usb-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	"open list:COMMON INTERNET F..."
	<linux-cifs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	"moderated list:COMMON INTERNET F..."
	<samba-technical-w/Ol4Ecudpl8XjKLYN78aQ@public.gmane.org>
Subject: Re: [PATCH] Use memzero_explicit to clear local buffers
Date: Mon, 5 Jan 2015 08:35:38 +1100	[thread overview]
Message-ID: <20150104213538.GA19906@gondor.apana.org.au> (raw)
In-Reply-To: <1420394744-20268-1-git-send-email-me-sZ9Uef1cvPWHXe+LvDLADg@public.gmane.org>

On Sun, Jan 04, 2015 at 07:05:40PM +0100, Giel van Schijndel wrote:
> When leaving a function use memzero_explicit instead of memset(0) to
> clear locally allocated/owned buffers. memset(0) may be optimized away.
> 
> All of the affected buffers contain sensitive data, key material or
> derivatives of one of those two.

Nack.
 
> diff --git a/arch/x86/crypto/sha256_ssse3_glue.c b/arch/x86/crypto/sha256_ssse3_glue.c
> index 8fad72f..b616e63 100644
> --- a/arch/x86/crypto/sha256_ssse3_glue.c
> +++ b/arch/x86/crypto/sha256_ssse3_glue.c
> @@ -164,7 +164,7 @@ static int sha256_ssse3_final(struct shash_desc *desc, u8 *out)
>  		dst[i] = cpu_to_be32(sctx->state[i]);
>  
>  	/* Wipe context */
> -	memset(sctx, 0, sizeof(*sctx));
> +	memzero_explicit(sctx, sizeof(*sctx));

sctx does not point to stack memory so this is bogus.

Only stack memory cleared just before it goes out of scope needs
memzero_explicit.

Cheers,
-- 
Email: Herbert Xu <herbert-lOAM2aK0SrRLBo1qDEOMRrpzq4S04n8Q@public.gmane.org>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt

WARNING: multiple messages have this Message-ID (diff)
From: Herbert Xu <herbert@gondor.apana.org.au>
To: Giel van Schijndel <me@mortis.eu>
Cc: linux-kernel@vger.kernel.org,
	"David S. Miller" <davem@davemloft.net>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
	"maintainer:X86 ARCHITECTURE..." <x86@kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Steve French <sfrench@samba.org>,
	Rahul Bedarkar <rahulbedarkar89@gmail.com>,
	Thomas Pugliese <thomas.pugliese@gmail.com>,
	Randy Dunlap <rdunlap@infradead.org>,
	Julia Lawall <Julia.Lawall@lip6.fr>,
	"open list:CRYPTO API" <linux-crypto@vger.kernel.org>,
	"open list:CERTIFIED WIRELES..." <linux-usb@vger.kernel.org>,
	"open list:COMMON INTERNET F..." <linux-cifs@vger.kernel.org>,
	"moderated list:COMMON INTERNET F..." 
	<samba-technical@lists.samba.org>
Subject: Re: [PATCH] Use memzero_explicit to clear local buffers
Date: Mon, 5 Jan 2015 08:35:38 +1100	[thread overview]
Message-ID: <20150104213538.GA19906@gondor.apana.org.au> (raw)
In-Reply-To: <1420394744-20268-1-git-send-email-me@mortis.eu>

On Sun, Jan 04, 2015 at 07:05:40PM +0100, Giel van Schijndel wrote:
> When leaving a function use memzero_explicit instead of memset(0) to
> clear locally allocated/owned buffers. memset(0) may be optimized away.
> 
> All of the affected buffers contain sensitive data, key material or
> derivatives of one of those two.

Nack.
 
> diff --git a/arch/x86/crypto/sha256_ssse3_glue.c b/arch/x86/crypto/sha256_ssse3_glue.c
> index 8fad72f..b616e63 100644
> --- a/arch/x86/crypto/sha256_ssse3_glue.c
> +++ b/arch/x86/crypto/sha256_ssse3_glue.c
> @@ -164,7 +164,7 @@ static int sha256_ssse3_final(struct shash_desc *desc, u8 *out)
>  		dst[i] = cpu_to_be32(sctx->state[i]);
>  
>  	/* Wipe context */
> -	memset(sctx, 0, sizeof(*sctx));
> +	memzero_explicit(sctx, sizeof(*sctx));

sctx does not point to stack memory so this is bogus.

Only stack memory cleared just before it goes out of scope needs
memzero_explicit.

Cheers,
-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt

  parent reply	other threads:[~2015-01-04 21:35 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-01-04 18:05 [PATCH] Use memzero_explicit to clear local buffers Giel van Schijndel
     [not found] ` <1420394744-20268-1-git-send-email-me-sZ9Uef1cvPWHXe+LvDLADg@public.gmane.org>
2015-01-04 21:35   ` Herbert Xu [this message]
2015-01-04 21:35     ` Herbert Xu
2015-01-04 22:49     ` Giel van Schijndel
2015-01-04 22:49       ` Giel van Schijndel
     [not found]       ` <20150104224909.GB4806-zsKMh+JvXepbNiWYSlF1AbANlwIBtoSN@public.gmane.org>
2015-01-04 23:36         ` Herbert Xu
2015-01-04 23:36           ` Herbert Xu
2015-01-05 17:36           ` Daniel Borkmann
2015-01-06 19:42           ` Giel van Schijndel
2015-01-06 19:42             ` Giel van Schijndel
     [not found]             ` <20150106194226.GM4806-zsKMh+JvXepbNiWYSlF1AbANlwIBtoSN@public.gmane.org>
2015-01-06 20:54               ` Herbert Xu
2015-01-06 20:54                 ` Herbert Xu
2015-01-04 23:05 ` Giel van Schijndel
2015-01-04 23:05   ` Giel van Schijndel
2015-01-06 21:37 ` [PATCH RESEND] cifs: use memzero_explicit to clear stack buffer Giel van Schijndel
2015-01-06 22:59   ` Herbert Xu
2015-01-06 22:59     ` Herbert Xu
2015-01-13  0:12     ` Steve French
2015-01-13  0:12       ` Steve French
2015-01-09 18:53   ` Steve French
2015-01-09 18:53     ` Steve French

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