linux-kernel - Re: [RFC PATCH 06/16] x86/efi: Generating random HMAC key for siging hibernate image

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Date:	Thu, 30 Jul 2015 17:20:46 +0100
From:	Matt Fleming <matt.fleming@...el.com>
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@...k.pl>,
	"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>, Jiri Kosina <jkosina@...e.cz>,
	"H. Peter Anvin" <hpa@...or.com>, "Lee, Chun-Yi" <jlee@...e.com>
Subject: Re: [RFC PATCH 06/16] x86/efi: Generating random HMAC key for
 siging hibernate image

On Thu, 2015-07-16 at 22:25 +0800, Lee, Chun-Yi wrote:
> This patch adds codes in EFI stub for generating and storing the
> HMAC key in EFI boot service variable for signing hibernate image.
> 
> Per rcf2104, the length of HMAC-SHA1 hash result is 20 bytes, and
> it recommended the length of key the same with hash rsult, means
> also 20 bytes. Using longer key would not significantly increase
> the function strength. Due to the nvram space is limited in some
> UEFI machines, so using the minimal recommended length 20 bytes
> key that will stored in boot service variable.
> 
> For generating a messy number as a 20 bytes key, the codes in EFI
> stub gets u32 random number five time and every random number is
> rolling that last u32 random number as entropy.
> 
> The HMAC key stored in EFI boot service variable, the GUID is
> S4SignKey-fe141863-c070-478e-b8a3-878a5dc9ef21.

[...]

> @@ -1383,6 +1384,60 @@ free_mem_map:
>  	return status;
>  }
>  
> +#ifdef CONFIG_HIBERNATE_VERIFICATION
> +#define SWSUSP_KEY \
> +	((efi_char16_t [10]) { 'S', 'W', 'S', 'U', 'S', 'P', 'K', 'e', 'y', 0 })
> +#define SWSUSP_KEY_ATTRIBUTE	(EFI_VARIABLE_NON_VOLATILE | \
> +				EFI_VARIABLE_BOOTSERVICE_ACCESS)

You mean "SWSUSPKey" not "S4SignKey" right?

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