linux-kernel - Re: [PATCH v2 04/16] x86/efi: Generating random number in EFI stub

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Message-ID: <20150827040637.GA24088@linux-rxt1.site>
Date:	Thu, 27 Aug 2015 12:06:37 +0800
From:	joeyli <jlee@...e.com>
To:	Matt Fleming <matt@...eblueprint.co.uk>
Cc:	"Lee, Chun-Yi" <joeyli.kernel@...il.com>,
	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>
Subject: Re: [PATCH v2 04/16] x86/efi: Generating random number in EFI stub

Hi Matt, 

Thanks for your reviewing and sorry for my delay.

On Thu, Aug 20, 2015 at 03:12:21PM +0100, Matt Fleming wrote:
> On Tue, 11 Aug, at 02:16:24PM, Lee, Chun-Yi wrote:
> > This patch adds the codes for generating random number array as the
> > HMAC key that will used by later EFI stub codes.
> > 
> > The original codes in efi_random copied from aslr and add the codes
> > to accept input entropy and EFI debugging. In later patch will add
> > the codes to get random number by EFI protocol. The separate codes
> > can avoid impacting aslr function.
>  
> Is there some way we can share the code between aslr and the EFI boot
> stub? People may not review both files when making changes and so bug
> fixes to one might not appear in the other.
> 
> -- 
> Matt Fleming, Intel Open Source Technology Center

The origin design is base on get_random_long() from aslr, so I direct
copy it to efi_random.c then modified it. 
There have some reasons I didn't share the code with aslr:

 - There have some debug_puttstr() for debugging in aslr, but those
   debugging log do not work in EFI stub, and I want put efi_print
   for debugging purpose. I don't want affect the code in aslr, so
   I choice copy get_random_long() to efi_random.c specific for EFI stub.

 - In subsequent patches add EFI random protocol support to
   get_random_longh().

In next version, I will try to extract shared code to misc.c to reuse them
between aslr and efi_random.


Thanks a lot!
Joey Lee
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