On Mon, Apr 20, 2020 at 01:57:51PM -0400, Joe Lawrence wrote:
> On Fri, Apr 17, 2020 at 09:04:27AM -0500, Josh Poimboeuf wrote:
> >
> > [ ... snip ... ]
> >
> > diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
> > index 40cfac8156fd..5fda3afc0285 100644
> > --- a/kernel/livepatch/core.c
> > +++ b/kernel/livepatch/core.c
> >
> > [ ... snip ... ]
> >
> > +int klp_write_relocations(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
> > + const char *shstrtab, const char *strtab,
> > + unsigned int symndx, struct module *pmod,
> > + const char *objname)
> > {
> > int i, cnt, ret = 0;
> > - const char *objname, *secname;
> > char sec_objname[MODULE_NAME_LEN];
> > Elf_Shdr *sec;
> >
> > - if (WARN_ON(!klp_is_object_loaded(obj)))
> > - return -EINVAL;
> > -
> > - 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;
> > + for (i = 1; i < ehdr->e_shnum; i++) {
> > + sec = sechdrs + i;
>
> Hi Josh, minor bug:
>
> Note the for loop through the section headers in
> klp_write_relocations(), but its calling function ...
>
> > [ ... snip ... ]
> >
> > diff --git a/kernel/module.c b/kernel/module.c
> > index 646f1e2330d2..d36ea8a8c3ec 100644
> > --- a/kernel/module.c
> > +++ b/kernel/module.c
> > @@ -2334,11 +2334,12 @@ static int apply_relocations(struct module *mod, const struct load_info *info)
> > if (!(info->sechdrs[infosec].sh_flags & SHF_ALLOC))
> > continue;
> >
> > - /* Livepatch relocation sections are applied by livepatch */
> > if (info->sechdrs[i].sh_flags & SHF_RELA_LIVEPATCH)
> > - continue;
> > -
> > - if (info->sechdrs[i].sh_type == SHT_REL)
> > + err = klp_write_relocations(info->hdr, info->sechdrs,
> > + info->secstrings,
> > + info->strtab,
> > + info->index.sym, mod, NULL);
> > + else if (info->sechdrs[i].sh_type == SHT_REL)
> > err = apply_relocate(info->sechdrs, info->strtab,
> > info->index.sym, i, mod);
> > else if (info->sechdrs[i].sh_type == SHT_RELA)
>
> ... apply_relocations() is also iterating over the section headers (the
> diff context doesn't show it here, but i is an incrementing index over
> sechdrs[]).
>
> So if there is more than one KLP relocation section, we'll process them
> multiple times. At least the x86 relocation code will detect this and
> fail the module load with an invalid relocation (existing value not
> zero).
Ah, yes, good catch!
--
Josh
