Hi Mimi, On 16/10/2019 02:44, Mimi Zohar wrote: > On Tue, 2019-10-15 at 18:39 +0100, James Morse wrote: >> If SecureBoot isn't relevant, I'm confused as to why kexec_file_load() is. >> >> I thought kexec_file_load() only existed because SecureBoot systems need to >> validate the >> new OS images's signature before loading it, and we can't trust user-space >> calling Kexec >> to do this. >> >> If there is no secure boot, why does this thing only work with >> kexec_file_load()? >> (good news! With the UEFI memreseve table, it should work transparently with >> regular kexec >> too)
> I'm so sorry for the confusion. IMA was originally limited to > extending trusted boot concepts to the OS. As of Linux 3.10, IMA > added support for extending secure boot concepts and auditing file > hashes (commit e7c568e0fd0cf). > > True, kexec_file_load is required for verifying the kexec kernel > image, but it is also required for measuring the kexec kernel image as > well. > > After reading the kernel image into memory (kernel_read_file_from_fd), > the hash is calculated and then added to the IMA measurement list and > used to extend the TPM. All of this is based on the IMA policy, > including the TPM PCR. Don't we get a set of segments with the regular kexec syscall? These could equally be hashed and measured, and logged via IMA and/or extending the TPMs measurements. (obviously this would include the command-line and maybe purgatory, which makes it less predictable, but these are still the binary blobs that were given privileged access to the system). >>> I am not sure if i addressed all your concerns, please let me know >>> if i missed anything. To me most concerns look to be towards the kexec case >>> and dependency >>> on hardware(ACPI/TPM) during boot and early boot services, where as >>> carrying the logs is >>> only during the kexec_file_load sys call and does not interfere with that >>> code path. >>> IMA documentation: https://sourceforge.net/p/linux-ima/wiki/Home/ >> >> Supporting ACPI in the same way is something we need to do from day one. >> kexec_file_load() >> already does this. I'm not sure "only kexec_file_load()" is a justifiable >> restriction... > The TPM PCRs are not reset on a soft reboot. As a result, in order to > validate the IMA measurement list against the TPM PCRs, the IMA > measurement list is saved on kexec load, restored on boot, and then > the memory allocated for carrying the measurement list across kexec is > freed. Hmm, this is why the reserved memory gets freed. What happens to stuff that happens between kexec-load and boot? There is a comment: | /* segment size can't change between kexec load and execute */ But I can't see anywhere that enforces that. I guess those measurements will go missing, and the TPM value will not match after kexec. Thanks, James _______________________________________________ kexec mailing list [email protected] http://lists.infradead.org/mailman/listinfo/kexec
