Hi Akashi, I'm still getting my head round how all this works, so please forgive what may be stupid questions! On 04/12/17 02:57, AKASHI Takahiro wrote: > This is the seventh round of implementing kexec_file_load() support > on arm64.[1] > Most of the code is based on kexec-tools (along with some kernel code > from x86, which also came from kexec-tools). > > > This patch series enables us to > * load the kernel, Image, via kexec_file_load() system call, and > * optionally verify its signature at load time for trusted boot. Is kdump using kexec_file_load() possible? (questions on patch 3) I can't work out why additional elf-generating code would be necessary if kdump works today without it... > To load the kernel via kexec_file_load() system call, a small change > is also required on kexec-tools. See [2]. This enables '-s' option. > (Please use v7.2.1+ crash utility for v4.14+ kernel) (what does the -s option do?) > As we discussed a long time ago, users may not be allowed to specify > device-tree file of the 2nd kernel explicitly with kexec-tools, hence > re-using the blob of the first kernel. > > Regarding a kernel image verification, a signature must be presented > along with the binary itself. A signature is basically a hash value > calculated against the whole binary data and encrypted by a key which > will be authenticated by the system's trusted certificate. > Any attempt to read and load a to-be-kexec-ed kernel image through > a system call will be checked and blocked if the binary's hash value > doesn't match its associated signature. > Concerns(or future works): (lets keep this stuff in the future) > * Even if the kernel is configured with CONFIG_RANDOMIZE_BASE, the 2nd > kernel won't be placed at a randomized address. We will have to > add some boot code similar to efi-stub to implement the randomization. I think there are two parts to this. The efistub may copy the kernel to a new ~random location in physical memory. It also adds a seed used to randomise the virtual-addresses the kernel executes from. For kexec_file_load() the first-kernel could apply some randomness to the physical offset when it re-assembles the kexec-kernel. i.e. code in arm64_relocate_new_kernel(). I don't think we should do this without some hint that the new kernel supports this... For the virtual-addresses it would need to add a new kaslr-seed to the DT/chosen, which should be harmless. > for approach (1), > * While big-endian kernel can support kernel signing, I'm not sure that > Image can be recognized as in PE format because x86 standard only > defines little-endian-based format. What does the recognizing? (I don't think we should invent a new format..) > * vmlinux support (Patch 3 is why I'm here) I don't think we need to support this. I can't boot a vmlinux file via UEFI. As I understand it kexec_file_load() is all about the signature verification for UEFI:SecureBoot. The chances of me having a vmlinux signed for SecureBoot use is pretty low, chances are its a self-signed image I just built, in which case I can use the arm64 Image file that was built at the same time. Supporting two file formats is going to be a headache. Distributions ship separate debug info packages for debugging, I don't think we need to make them bootable... Thanks, James _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
