On 07/14/16 at 02:38am, AKASHI Takahiro wrote: > Apologies for the slow response. I'm attending LinuxCon this week. > > On Wed, Jul 13, 2016 at 10:34:47AM +0100, Mark Rutland wrote: > > On Wed, Jul 13, 2016 at 10:36:14AM +0800, Dave Young wrote: > > > But consider we can kexec to a different kernel and a different initrd so there > > > will be use cases to pass a total different dtb as well. > > > > It depends on what you mean by "a different kernel", and what this > > implies for the DTB. > > > > I expect future arm64 Linux kernels to function with today's DTBs, and > > the existing boot protocol. The kexec_file_load syscall already has > > enough information for the kernel to inject the initrd and bootargs > > properties into a DTB. > > > > In practice on x86 today, kexec_file_load only supports booting to a > > Linux kernel, because the in-kernel purgatory only implements the x86 > > Linux boot protocol. Analagously, for arm64 I think that the first > > kernel should use its internal copy of the boot DTB, with /chosen fixed > > up appropriately, assuming the next kernel is an arm64 Linux image. > > > > If booting another OS, the only parts of the DTB I would expect to > > change are the properties under chosen, as everything else *should* be > > OS-independent. However the other OS may have a completely different > > boot protocol, might not even take a DTB, and will likely need a > > compeltely different purgatory implementation. So just allowing the DTB > > to be altered isn't sufficient for that case. > > > > There might be cases where we want a different DTB, but as far as I can > > tell we have nothing analagous on x86 today. If we do need this, we > > should have an idea of what real case(s) were trying to solve. > > What I had in my mind was: > > - Kdump > As Russel said, we definitely need to modify dtb. > In addition to bootargs and initrd proerties (FYI, in my arm64 > implementation for arm64, eflcorehdr info is also passed as DT > property), we may want to remove unnecessary devices and > even add a dedicated storage device for storing a core dump image. > - Say, booting BE kernel on ACPI LE kernel > In this case, there is no useful dtb in the kernel. > > Have said that, as Mark said, we may be able to use normal kexec_load > system call if we don't need a "secure" kexec. > > BTW, why doesn't the current kexec_load have ability of verifying > a signature of initramfs image? Is IMA/EVM expected to be used > at runtime? I believe there are some limitations for verify signatures in kexec_load. First kexec-tools need to be trusted, but there's no way to sign and verify signature of shared libraries. There maybe other limitations I can not remember which are also reasons why Vivek moved to current file based syscall. Thanks Dave
