linux-kernel - Re: [PATCH 5.4 regression fix] x86/boot: Provide memzero

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Date:   Mon, 07 Oct 2019 10:59:19 +0200
From:   Stephan Mueller <smueller@...onox.de>
To:     Hans de Goede <hdegoede@...hat.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        linux-crypto@...r.kernel.org, x86@...nel.org,
        linux-kernel@...r.kernel.org, Arvind Sankar <nivedita@...m.mit.edu>
Subject: Re: [PATCH 5.4 regression fix] x86/boot: Provide memzero_explicit

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@...m.mit.edu>
> Fixes: 906a4bb97f5d ("crypto: sha256 - Use get/put_unaligned_be32 to get
> input, memzero_explicit") Signed-off-by: Hans de Goede
> <hdegoede@...hat.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