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From:   Stephan Mueller <smueller@chronox.de>
To:     Hans de Goede <hdegoede@redhat.com>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H . Peter Anvin" <hpa@zytor.com>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        linux-crypto@vger.kernel.org, x86@kernel.org,
        linux-kernel@vger.kernel.org, Arvind Sankar <nivedita@alum.mit.edu>
Subject: Re: [PATCH 5.4 regression fix] x86/boot: Provide memzero_explicit
Date:   Mon, 07 Oct 2019 10:59:19 +0200
Message-ID: <65461301.CAtk0GNLiE@tauon.chronox.de>
In-Reply-To: <20191007085501.23202-1-hdegoede@redhat.com>
References: <20191007085501.23202-1-hdegoede@redhat.com>
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Am Montag, 7. Oktober 2019, 10:55:01 CEST schrieb Hans de Goede:

Hi Hans,

> The purgatory code now uses the shared lib/crypto/sha256.c sha256
> implementation. This needs memzero_explicit, implement this.
> 
> Reported-by: Arvind Sankar <nivedita@alum.mit.edu>
> Fixes: 906a4bb97f5d ("crypto: sha256 - Use get/put_unaligned_be32 to get
> input, memzero_explicit") Signed-off-by: Hans de Goede
> <hdegoede@redhat.com>
> ---
>  arch/x86/boot/compressed/string.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/arch/x86/boot/compressed/string.c
> b/arch/x86/boot/compressed/string.c index 81fc1eaa3229..511332e279fe 100644
> --- a/arch/x86/boot/compressed/string.c
> +++ b/arch/x86/boot/compressed/string.c
> @@ -50,6 +50,11 @@ void *memset(void *s, int c, size_t n)
>  	return s;
>  }
> 
> +void memzero_explicit(void *s, size_t count)
> +{
> +	memset(s, 0, count);

May I ask how it is guaranteed that this memset is not optimized out by the 
compiler, e.g. for stack variables?
> +}
> +
>  void *memmove(void *dest, const void *src, size_t n)
>  {
>  	unsigned char *d = dest;


Ciao
Stephan