The per-CPU data section is handled differently than the other sections. The memory allocations requires a special __percpu pointer and then the section is copied into the view of each CPU. Therefore the SHF_ALLOC flag is removed to ensure move_module() skips it.
Later, relocations are applied and apply_relocations() skips sections without SHF_ALLOC because they have not been copied. This also skips the per-CPU data section. The missing relocations result in a NULL pointer on x86-64 and very small values on x86-32. This results in a crash because it is not skipped like NULL pointer would and it can't be dereferenced. Such an assignment happens during compile time per-CPU lock initialisation with lockdep enabled. Add the SHF_ALLOC flag back for the per-CPU section after move_module(). Reported-by: kernel test robot <oliver.s...@intel.com> Closes: https://lore.kernel.org/oe-lkp/202506041623.e45e4f7d-...@intel.com Fixes: 8d8022e8aba85 ("module: do percpu allocation after uniqueness check. No, really!") Signed-off-by: Sebastian Andrzej Siewior <bige...@linutronix.de> --- kernel/module/main.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/kernel/module/main.c b/kernel/module/main.c index 5c6ab20240a6d..35abb5f13d7dc 100644 --- a/kernel/module/main.c +++ b/kernel/module/main.c @@ -2816,6 +2816,9 @@ static struct module *layout_and_allocate(struct load_info *info, int flags) if (err) return ERR_PTR(err); + /* Add SHF_ALLOC back so that relocations are applied. */ + info->sechdrs[info->index.pcpu].sh_flags |= SHF_ALLOC; + /* Module has been copied to its final place now: return it. */ mod = (void *)info->sechdrs[info->index.mod].sh_addr; kmemleak_load_module(mod, info); -- 2.49.0
