linux-kernel - Re: [PATCH v2 05/16] x86/efi: Get entropy through EFI random number generator protocol

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Message-ID: <20150820202620.GF2567@codeblueprint.co.uk>
Date:	Thu, 20 Aug 2015 21:26:20 +0100
From:	Matt Fleming <matt@...eblueprint.co.uk>
To:	"Lee, Chun-Yi" <joeyli.kernel@...il.com>
Cc:	linux-kernel@...r.kernel.org, linux-efi@...r.kernel.org,
	linux-pm@...r.kernel.org, "Rafael J. Wysocki" <rjw@...ysocki.net>,
	Matthew Garrett <matthew.garrett@...ula.com>,
	Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
	Josh Boyer <jwboyer@...hat.com>,
	Vojtech Pavlik <vojtech@...e.cz>,
	Matt Fleming <matt.fleming@...el.com>,
	Jiri Kosina <jkosina@...e.cz>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
	"Lee, Chun-Yi" <jlee@...e.com>
Subject: Re: [PATCH v2 05/16] x86/efi: Get entropy through EFI random number
 generator protocol

On Tue, 11 Aug, at 02:16:25PM, Lee, Chun-Yi wrote:
> +
> +static unsigned long efi_get_rng64(efi_system_table_t *sys_table,
> +				   void **rng_handle)
> +{
> +	const struct efi_config *efi_early = __efi_early();
> +	efi_rng_protocol_64 *rng = NULL;
> +	efi_guid_t rng_proto = EFI_RNG_PROTOCOL_GUID;
> +	u64 *handles = (u64 *)(unsigned long)rng_handle;
> +	efi_status_t status;
> +	unsigned long rng_number;
> +
> +	status = efi_call_early(handle_protocol, handles[0],
> +				&rng_proto, (void **)&rng);
> +	if (status != EFI_SUCCESS)
> +		efi_printk(sys_table, "Failed to get EFI_RNG_PROTOCOL handles\n");
> +
> +	if (status == EFI_SUCCESS && rng) {
> +		status = efi_early->call((unsigned long)rng->get_rng, rng, NULL,
> +					sizeof(rng_number), &rng_number);

Actually, one thing just occurred to me - you're not passing an
RNGAlgorithm value and are relying upon the firmware's default
implementation.

I don't think that's a safe bet, the default could be anything and
might vary across implementations.

Can we do a little better here and pick a "preferred" algorithm
instead of the default?

-- 
Matt Fleming, Intel Open Source Technology Center
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