On Tue, Jul 12, 2016 at 10:58:09AM -0300, Thiago Jung Bauermann wrote: > Hello Eric, > > Am Dienstag, 12 Juli 2016, 08:25:48 schrieb Eric W. Biederman: > > AKASHI Takahiro <takahiro.akashi at linaro.org> writes: > > > Device tree blob must be passed to a second kernel on DTB-capable > > > archs, like powerpc and arm64, but the current kernel interface > > > lacks this support. > > > > > > This patch extends kexec_file_load system call by adding an extra > > > argument to this syscall so that an arbitrary number of file descriptors > > > can be handed out from user space to the kernel. > > > > > > See the background [1]. > > > > > > Please note that the new interface looks quite similar to the current > > > system call, but that it won't always mean that it provides the "binary > > > compatibility." > > > > > > [1] http://lists.infradead.org/pipermail/kexec/2016-June/016276.html > > > > So this design is wrong. The kernel already has the device tree blob, > > you should not be extracting it from the kernel munging it, and then > > reinserting it in the kernel if you want signatures and everything to > > pass. > > > > What x86 does is pass it's equivalent of the device tree blob from one > > kernel to another directly and behind the scenes. It does not go > > through userspace for this. > > > > Until a persuasive case can be made for going around the kernel and > > probably adding a feature (like code execution) that can be used to > > defeat the signature scheme I am going to nack this. > > There are situations where userspace needs to change things in the device > tree to be used by the next kernel. > > For example, Petitboot (the boot loader used in OpenPOWER machines) is a > userspace application running in an intermediary Linux instance and uses > kexec to load the target OS. It has to modify the device tree that will be > used by the next kernel so that the next kernel uses the same console that > petitboot was configured to use (i.e., set the /chosen/linux,stdout-path > property). It also modifies the device tree to allow the kernel to inherit > Petitboot's Openfirmware framebuffer. Can some of this be done with the help of kernel command line options for second kernel? Vivek
