On Tue 2020-02-25 11:05:39, Miroslav Benes wrote: > CC live-patching ML, because this could affect many of its users... > > On Fri, 21 Feb 2020, Will Deacon wrote: > > > Hi folks, > > > > Despite having just a single modular in-tree user that I could spot, > > kallsyms_lookup_name() is exported to modules and provides a mechanism > > for out-of-tree modules to access and invoke arbitrary, non-exported > > kernel symbols when kallsyms is enabled. Just to explain how this affects livepatching users. Livepatch is a module that inludes fixed copies of functions that are buggy in the running kernel. These functions often call functions or access variables that were defined static in the original source code. There are two ways how this is currently solved. Some livepatch authors use kallsyms_lookup_name() to locate the non-exported symbols in the running kernel and then use these address in the fixed code. Another possibility is to used special relocation sections, see Documentation/livepatch/module-elf-format.rst The problem with the special relocations sections is that the support to generate them is not ready yet. The main piece would klp-convert tool. Its development is pretty slow. The last version can be found at https://lkml.kernel.org/r/20190509143859.9050-1-joe.lawrence@xxxxxxxxxx I am not sure if this use case is enough to keep the symbols exported. Anyway, there are currently some out-of-tree users. Best Regards, Petr
