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From: Ingo Molnar <mingo@kernel.org>
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 v2 5.4 regression fix] x86/boot: Provide memzero_explicit
Date: Mon, 7 Oct 2019 16:00:22 +0200
Message-ID: <20191007140022.GA29008@gmail.com> (raw)
In-Reply-To: <20191007134724.4019-1-hdegoede@redhat.com>


* Hans de Goede <hdegoede@redhat.com> wrote:

> 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>
> ---
> Changes in v2:
> - Add barrier_data() call after the memset, making the function really
>   explicit. Using barrier_data() works fine in the purgatory (build)
>   environment.
> ---
>  arch/x86/boot/compressed/string.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/arch/x86/boot/compressed/string.c b/arch/x86/boot/compressed/string.c
> index 81fc1eaa3229..654a7164a702 100644
> --- a/arch/x86/boot/compressed/string.c
> +++ b/arch/x86/boot/compressed/string.c
> @@ -50,6 +50,12 @@ void *memset(void *s, int c, size_t n)
>  	return s;
>  }
>  
> +void memzero_explicit(void *s, size_t count)
> +{
> +	memset(s, 0, count);
> +	barrier_data(s);
> +}

So the barrier_data() is only there to keep LTO from optimizing out the 
seemingly unused function?

Is there no canonical way to do that, instead of a seemingly obscure 
barrier_data() call - which would require a comment at minimum.

We do have $(DISABLE_LTO), not sure whether it's applicable here though.

Thanks,

	Ingo

  reply index

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-07 13:47 Hans de Goede
2019-10-07 14:00 ` Ingo Molnar [this message]
2019-10-07 14:11   ` Hans de Goede
2019-10-07 14:22     ` Ingo Molnar
2019-10-07 14:29       ` Hans de Goede
2019-10-07 14:46         ` Ingo Molnar
2019-10-07 15:20           ` Arvind Sankar
2019-10-07 15:40             ` Ingo Molnar
2019-10-07 18:42               ` Arvind Sankar
2019-10-07 19:36                 ` Hans de Goede
2019-10-07 22:00                   ` [PATCH] lib/string: make memzero_explicit inline instead of external Arvind Sankar
2019-10-08 11:33                     ` [tip: x86/urgent] lib/string: Make memzero_explicit() " tip-bot2 for Arvind Sankar
2019-10-08 11:33                     ` tip-bot2 for Arvind Sankar
2019-10-10  2:52                     ` [PATCH] lib/string: make memzero_explicit " Dave Young
2019-10-10  6:56                       ` Dave Young
2019-10-07 14:49 ` [tip: x86/urgent] x86/boot: Provide memzero_explicit() tip-bot2 for Hans de Goede
2019-10-07 14:49 ` tip-bot2 for Hans de Goede

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