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 can't be dereferenced. Such an assignment happens during static per-CPU lock initialisation with lockdep enabled. Allow relocation processing for the per-CPU section even if SHF_ALLOC is missing. Reported-by: kernel test robot <oliver.s...@intel.com> Closes: https://lore.kernel.org/oe-lkp/202506041623.e45e4f7d-...@intel.com Fixes: 1a6100caae425 ("Don't relocate non-allocated regions in modules.") #v2.6.1-rc3 Signed-off-by: Sebastian Andrzej Siewior <bige...@linutronix.de> --- v2…v3: https://lore.kernel.org/all/20250605060738.sza3u...@linutronix.de/ - Check for assigned per-CPU section instead of adding the SHF_ALLOC flag back. v1…v2: https://lore.kernel.org/all/20250604152707.cied9...@linutronix.de/ - Add the flag back only on SMP if the per-CPU section was found. kernel/module/main.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/kernel/module/main.c b/kernel/module/main.c index 413ac6ea37021..cb281e82226cd 100644 --- a/kernel/module/main.c +++ b/kernel/module/main.c @@ -1573,8 +1573,14 @@ static int apply_relocations(struct module *mod, const struct load_info *info) if (infosec >= info->hdr->e_shnum) continue; - /* Don't bother with non-allocated sections */ - if (!(info->sechdrs[infosec].sh_flags & SHF_ALLOC)) + /* + * Don't bother with non-allocated sections. + * An exception is the percpu section, which has separate allocations + * for individual CPUs. We relocate the percpu section in the initial + * ELF template and subsequently copy it to the per-CPU destinations. + */ + if (!(info->sechdrs[infosec].sh_flags & SHF_ALLOC) && + (!infosec || infosec != info->index.pcpu)) continue; if (info->sechdrs[i].sh_flags & SHF_RELA_LIVEPATCH) -- 2.49.0
