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Re: [PATHC v2 0/9] ima: carry the measurement list across kexec

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  Re: [PATHC v2 0/9] ima: carry the measurement list across kexec Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com> - 2016-09-26 20:40 +0200
    Re: [PATHC v2 0/9] ima: carry the measurement list across kexec ebiederm@xmission.com (Eric W. Biederman) - 2016-09-29 23:50 +0200
      Re: [PATHC v2 0/9] ima: carry the measurement list across kexec Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com> - 2016-09-30 00:30 +0200

#1491500 — Re: [PATHC v2 0/9] ima: carry the measurement list across kexec

Hello Eric,

Am Dienstag, 20 September 2016, 11:07:29 schrieb Eric W. Biederman:
> Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com> writes:
> > Am Samstag, 17 September 2016, 00:17:37 schrieb Eric W. Biederman:
> >> Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com> writes:
> > Is this what you had in mind?
> 
> Sort of.
> 
> I was just thinking that instead of having the boot path verify your ima
> list matches what is in the tpm and halting the boot there, we could
> test that on reboot.  Which would give a clean failure without the nasty
> poking into a prepared image.  The downside is that we have already run
> the shutdown scripts so it wouldn't be much cleaner, than triggering a
> machine reboot from elsewhere.
> 
> But I don't think we should spend too much time on that.  It was a
> passing thought.  We should focus on getting a non-poked ima buffer
> cleanly into kexec and we can worry about the rest later.

I was thinking of this as something orthogonal to the ima buffer feature.
But you're right, it's better not to discuss this now. I'll post a separate 
patch for this later.

> >> So from 10,000 feet I think that is correct.
> >> 
> >> I am not quite certain why a new mechanism is being invented.  We have
> >> other information that is already passed (much of it architecture
> >> specific) like the flattened device tree.  If you remove the need to
> >> update the information can you just append this information to the
> >> flattened device tree without a new special mechanism to pass the data?
> >> 
> >> I am just reluctant to invent a new mechanism when there is an existing
> >> mechanism that looks like it should work without problems.
> > 
> > Michael Ellerman suggested putting the buffer contents inside the device
> > tree itself, but the s390 people are also planning to implement this
> > feature. That architecture doesn't use device trees, so a solution that
> > depends on DTs won't help them.
> > 
> > With this mechanism each architecture will still need its own way of
> > communicating to the next kernel where the buffer is, but I think it's
> > easier to pass a base address and length than to pass a whole buffer.
> 
> A base address and length pair is fine.  There are several other pieces
> of data that we pass that way.
> 
> > I suppose we could piggyback the ima measurements buffer at the end of
> > one of the other segments such as the kernel or, in the case of
> > powerpc, the dtb but it looks hackish to me. I think it's cleaner to
> > put it in its own segment.
> 
> The boot protocol unfortunately is different on different architectures,
> and for each one we will have to implement and document the change.
> Because when you get into boot protocol issues you can't assume the
> kernel you are booting is the same version as the kernel that is booting
> it.
> 
> Where I run into a problem is you added a semi-generic concept a
> hand-over buffer.  Not a ima data buffer but a hand-over buffer.
> 
> The data falling in it's own dedicated area of memory and being added
> with kexec_add_buffer is completely fine.  I can see a dedicated pointer
> in struct kimage if necessary.
> 
> A semi-generic concept called a hand-over buffer seems to be a
> construction of infrustructure for no actual reason that will just
> result in confusion.  There are lots of things that are handed over, the
> flattend device tree, ramdisks, bootparams on x86, etc, etc.  ima is not
> special in this execpt for being perhaps the first addition that we are
> going to want the option of including on most architectures.

Ok, I understand. I decided to implement a generic concept because I thought 
that proposing a feature that is more useful than what I need it for would  
increase its chance of being accepted. It's interesting to see that it had 
the opposite effect.

I reworked and simplified the code and folded the hand-over buffer patches 
into Mimi's patch series to carry the measurement list across kexec. The 
kexec buffer code is in the following patches now:

[PATCH v5 01/10] powerpc: ima: Get the kexec buffer passed by the previous 
kernel
[PATCH v5 05/10] powerpc: ima: Send the kexec buffer to the next kernel

Each patch has a changelog listing what I changed to make it specific to 
IMA.

-- 
[]'s
Thiago Jung Bauermann
IBM Linux Technology Center

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#1493737

Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com> writes:

> Hello Eric,
>
> Am Dienstag, 20 September 2016, 11:07:29 schrieb Eric W. Biederman:
>> A semi-generic concept called a hand-over buffer seems to be a
>> construction of infrustructure for no actual reason that will just
>> result in confusion.  There are lots of things that are handed over, the
>> flattend device tree, ramdisks, bootparams on x86, etc, etc.  ima is not
>> special in this execpt for being perhaps the first addition that we are
>> going to want the option of including on most architectures.
>
> Ok, I understand. I decided to implement a generic concept because I thought 
> that proposing a feature that is more useful than what I need it for would  
> increase its chance of being accepted. It's interesting to see that it had 
> the opposite effect.

Yes.  In this case it was not clear that anyone else could use it, and
being less generic you can tweak the needs of the code to ima without
anyone having to worry about it.

So thank you very much for making the code more specific to the circumstances.

> I reworked and simplified the code and folded the hand-over buffer patches 
> into Mimi's patch series to carry the measurement list across kexec. The 
> kexec buffer code is in the following patches now:
>
> [PATCH v5 01/10] powerpc: ima: Get the kexec buffer passed by the previous 
> kernel
> [PATCH v5 05/10] powerpc: ima: Send the kexec buffer to the next
> kernel

That plus  [PATCH v5 06/10] ima: on soft reboot, save the measurement list

> Each patch has a changelog listing what I changed to make it specific to 
> IMA.

I am a little sad to see you needed to modify kexec_file.c to get where
you were going, but that isn't a huge issue either way.

Eric

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#1493758

Am Donnerstag, 29 September 2016, 16:43:08 schrieb Eric W. Biederman:
> Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com> writes:
> > Hello Eric,
> > 
> > Am Dienstag, 20 September 2016, 11:07:29 schrieb Eric W. Biederman:
> >> A semi-generic concept called a hand-over buffer seems to be a
> >> construction of infrustructure for no actual reason that will just
> >> result in confusion.  There are lots of things that are handed over,
> >> the
> >> flattend device tree, ramdisks, bootparams on x86, etc, etc.  ima is
> >> not
> >> special in this execpt for being perhaps the first addition that we are
> >> going to want the option of including on most architectures.
> > 
> > Ok, I understand. I decided to implement a generic concept because I
> > thought that proposing a feature that is more useful than what I need
> > it for would increase its chance of being accepted. It's interesting to
> > see that it had the opposite effect.
> 
> Yes.  In this case it was not clear that anyone else could use it, and
> being less generic you can tweak the needs of the code to ima without
> anyone having to worry about it.
> 
> So thank you very much for making the code more specific to the
> circumstances.

Thank you very much for your feedback and your reviews!

-- 
[]'s
Thiago Jung Bauermann
IBM Linux Technology Center

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