On Fri, Oct 25, 2019 at 08:17:41PM -0500, Josh Poimboeuf wrote:
> + * The following restrictions apply to module-specific relocation sections:
> + *
> + * a) References to vmlinux symbols are not allowed. Otherwise there might
> + * be module init ordering issues, and crashes might occur in some of the
> + * other kernel patching components like paravirt patching or jump
> + * labels. All references to vmlinux symbols should use either normal
> + * relas (for exported symbols) or vmlinux-specific klp relas (for
> + * unexported symbols). This restriction is enforced in
> + * klp_resolve_symbols().
Right.
> + * b) Relocations to special sections like __jump_table and .altinstructions
> + * aren't allowed. In other words, there should never be a
> + * .klp.rela.{module}.__jump_table section. This will definitely cause
> + * initialization ordering issues, as such special sections are processed
> + * during the loading of the klp module itself, *not* the to-be-patched
> + * module. This means that e.g., it's not currently possible to patch a
> + * module function which uses a static key jump label, if you want to
> + * have the replacement function also use the same static key. In this
> + * case, a non-static interface like static_key_enabled() can be used in
> + * the new function instead.
Idem for .static_call_sites I suppose..
Is there any enforcement on this? I'm thinking it should be possible to
detect the presence of these sections and yell a bit.
OTOH, it should be possible to actually handle this, but let's do that
later.
> + * On the other hand, a .klp.rela.vmlinux.__jump_table section is fine,
> + * as it can be resolved early enough during the load of the klp module,
> + * as described above.
> + */
> diff --git a/kernel/module.c b/kernel/module.c
> index fe5bd382759c..ff4347385f05 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -2327,11 +2327,9 @@ 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(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)
Like here, we can yell and error if .klp.rela.{mod}.__jump_table
sections are encountered.
Other than that, this should work I suppose.
