Re: [PATCH v6] livepatch: Clear relocation targets on a module removal

Miroslav Benes
2022-12-09T12:49:33Z

> > > --- a/kernel/livepatch/core.c
> > > +++ b/kernel/livepatch/core.c
> > > @@ -316,6 +316,45 @@ int klp_apply_section_relocs(struct module *pmod, Elf_Shdr *sechdrs,
> > > return apply_relocate_add(sechdrs, strtab, symndx, secndx, pmod);
> > > }
> > >
> > > +static void klp_clear_object_relocations(struct module *pmod,
> > > + struct klp_object *obj)
> > > +{
> > > + int i, cnt;
> > > + const char *objname, *secname;
> > > + char sec_objname[MODULE_NAME_LEN];
> > > + Elf_Shdr *sec;
> > > +
> > > + objname = klp_is_module(obj) ? obj->name : "vmlinux";
> > > +
> > > + /* For each klp relocation section */
> > > + for (i = 1; i < pmod->klp_info->hdr.e_shnum; i++) {
> > > + sec = pmod->klp_info->sechdrs + i;
> > > + secname = pmod->klp_info->secstrings + sec->sh_name;
> > > + if (!(sec->sh_flags & SHF_RELA_LIVEPATCH))
> > > + continue;
> > > +
> > > + /*
> > > + * Format: .klp.rela.sec_objname.section_name
> > > + * See comment in klp_resolve_symbols() for an explanation
> > > + * of the selected field width value.
> > > + */
> > > + secname = pmod->klp_info->secstrings + sec->sh_name;
> > > + cnt = sscanf(secname, ".klp.rela.%55[^.]", sec_objname);
> > > + if (cnt != 1) {
> > > + pr_err("section %s has an incorrectly formatted name\n",
> > > + secname);
> > > + continue;
> > > + }
>
> Actually, I think we don't need the cnt check here. Once it is removed,
> there isn't much duplicated logic.

Because it must have passed the check once already during
klp_apply_section_relocs()? Yes, perhaps.

Miroslav