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SubjectRe: [PATCH 1/7] ima: on soft reboot, restore the measurement list
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On Wed, 2016-08-10 at 19:52 +1000, Michael Ellerman wrote:
> Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com> writes:
>
> > Am Mittwoch, 10 August 2016, 13:41:08 schrieb Michael Ellerman:
> >> Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com> writes:
> >> > Am Dienstag, 09 August 2016, 09:01:13 schrieb Mimi Zohar:
> >> >> On Tue, 2016-08-09 at 20:59 +1000, Michael Ellerman wrote:
> >> >> > Mimi Zohar <zohar@linux.vnet.ibm.com> writes:
> >> >> > > +/* Some details preceding the binary serialized measurement list
> >> >> > > */
> >> >> > > +struct ima_kexec_hdr {
> >> >> > > + unsigned short version;
> >> >> > > + unsigned long buffer_size;
> >> >> > > + unsigned long count;
> >> >> > > +} __packed;
> >> >> > > +
> >> >> >
> >> >> > Am I understanding it correctly that this structure is passed between
> >> >> > kernels?
> >> >>
> >> >> Yes, the header prefixes the measurement list, which is being passed on
> >> >> the same computer to the next kernel. Could the architecture (eg.
> >> >> LE/BE) change between soft re-boots?
> >> >
> >> > Yes. I am able to boot a BE kernel from an LE kernel with my patches.
> >> > Whether we want to support that or not is another question...
> >>
> >> Yes you must support that. BE -> LE and vice versa.
> >
> > I didn't test BE - LE yet, but will do.
>
> Thanks.

Ok. There have been requests for making the binary_runtime_measurements
architecture independent. As this was not a network facing interface,
we left it in native format. With the kernel now consuming this data,
it makes sense for the binary_runtime_measurements to be in an
architecture independent format.

Unfortunately, as the <securityfs>/ima/binary_runtime_measurements is
not prefixed with any metadata, this change would need to be Kconfig
based, but kexec would always use the architecture independent format.

> >> You should also consider the possibility that the next kernel is not
> >> Linux.

Oh!

> > If the next kernel is an ELF binary and it supports the kexec "calling
> > convention", it should work too. What could possibly go wrong? I can try
> > FreeBSD (I suppose it's an ELF kernel) and see what happens.
>
> At least for old style kexec (not sys_kexec_load()) I don't think it
> even needs to be an ELF binary.
>
> I think there are folks working on FreeBSD (or $?BSD), so I think the
> basic kexec part works.
>
> There's nothing (yet) that wants to use this measurement list obviously,
> but it should be designed such that it could be used by an unknown
> future kernel that knows the ABI.
>
> So given what you have above, you'd use something like:
>
> struct ima_kexec_hdr {
> u16 version;
> u16 _reserved0;
> u32 _reserved1;
> u64 buffer_size;
> u64 count;
> };
>
> cheers

Thanks, I'll make this change.

Mimi

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