linux-kernel - Re: [PATCH 10/13] kexec: Load and Relocate purgatory at kernel load time

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Date:	Fri, 13 Jun 2014 18:14:47 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Vivek Goyal <vgoyal@...hat.com>, mjg59@...f.ucam.org
Cc:	linux-kernel@...r.kernel.org, kexec@...ts.infradead.org,
	ebiederm@...ssion.com, hpa@...or.com, greg@...ah.com,
	jkosina@...e.cz, dyoung@...hat.com, chaowang@...hat.com,
	bhe@...hat.com, akpm@...ux-foundation.org
Subject: Re: [PATCH 10/13] kexec: Load and Relocate purgatory at kernel load
 time

On Wed, Jun 11, 2014 at 03:24:48PM -0400, Vivek Goyal wrote:
> This new syscall requires sha256 even if signature checking does not
> happen. Purgatory verifies checksum of segments.
> 
> I had to select CRYPTO also otherwise CONFIG_CRYPTO=m broke the build.
> 
> > 
> > Which begs the more important question - shouldn't this new in-kernel
> > loading method support also kexec'ing of kernels without any signature
> > verifications at all?
> 
> I think yes it should allow kexecing kernels without any signature also.
> In fact in long term, we should deprecate the old syscall and maintain
> this new one.
> 
> Now, when does signature checking kick in? I think we can define a new
> config option say KEXEC_ENFORCE_KERNEL_SIG_VERIFICATION. This option
> will make sure kernel signature are verified. 
> 
> If KEXEC_ENFORCE_KERNEL_SIG_VERIFICATION=n, even then signature
> verification should be enforced if secureboot is enabled on the platform.

Right, this makes sense to me. Probably Matthew might want to chime in
here too...

> I will make it configurable in next series. This series does not do
> any signature verification yet. Above CRYPTO and CRYPTO_SHA256 I had
> to select to make sure checksum verfication logic in purgatory works
> fine.

Ok.

> Hmm... I have seen at other places using same name as structure. But I am
> not particular about it will change. Anyway, on most of the places
> I use a pointer to access it.
> 
> struct purgaotry_info *pi  = &image->purgatory_info;

Yep, saw that in the later patches :)

> I would like to retain purgaotry_buf. To shorten it I could do this.
> 
> 	struct purgatory_info *pi = &image->purgatory_info;
> 	vfree(pi->purgatory_buf);
> 	pi->purgatory_buf = NULL;
> 
> I like the clarity in variable names.

Ok.

> I would like to keep it one function. Reason being that apart from
> digest, we also store the list of regions which has been checkummed. And
> you will notice that we skip the purgatory region during checksum
> calculation.
> 
> So I will have to return quite some information from calc() function. Size
> of digest, actual digest buffer which will need to be freed by caller,
> and list of sha regions which will need to be freed by caller. Keeping
> it call in one function makes it little simpler actually.

Hmm, ok.

> Just wanted a small zero buffer. Is there any global zero buffer
> available in kernel. If not, I could use a PAGE_SIZE zero buffer
> instead.

empty_zero_page?

Thanks.

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
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