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    SubjectRe: [PATCH] arm64/module: use mod->klp_info section header information
    On Tue 2018-10-23 19:55:54, Jessica Yu wrote:
    > The arm64 module loader keeps a pointer into info->sechdrs to keep track
    > of section header information for .plt section(s). A pointer to the
    > relevent section header (struct elf64_shdr) in info->sechdrs is stored
    > in mod->arch.{init,core}.plt. This pointer may be accessed while
    > applying relocations in apply_relocate_add() for example. And unlike
    > normal modules, livepatch modules can call apply_relocate_add() after
    > module load. But the info struct (and therefore info->sechdrs) gets
    > freed at the end of load_module() and so mod->arch.{init,core}.plt
    > becomes an invalid pointer after the module is done loading.
    >
    > Luckily, livepatch modules already keep a copy of Elf section header
    > information in mod->klp_info. So make sure livepatch modules on arm64
    > have access to the section headers in klp_info and set
    > mod->arch.{init,core}.plt to the appropriate section header in
    > mod->klp_info so that they can call apply_relocate_add() even after
    > module load.
    >
    > diff --git a/kernel/module.c b/kernel/module.c
    > index f475f30eed8c..f3ac04cc9fc3 100644
    > --- a/kernel/module.c
    > +++ b/kernel/module.c
    > @@ -3367,6 +3367,8 @@ int __weak module_finalize(const Elf_Ehdr *hdr,
    >
    > static int post_relocation(struct module *mod, const struct load_info *info)
    > {
    > + int err;
    > +
    > /* Sort exception table now relocations are done. */
    > sort_extable(mod->extable, mod->extable + mod->num_exentries);
    >
    > @@ -3377,8 +3379,18 @@ static int post_relocation(struct module *mod, const struct load_info *info)
    > /* Setup kallsyms-specific fields. */
    > add_kallsyms(mod, info);
    >
    > + if (is_livepatch_module(mod)) {
    > + err = copy_module_elf(mod, info);
    > + if (err < 0)
    > + return err;
    > + }
    > +
    > /* Arch-specific module finalizing. */
    > - return module_finalize(info->hdr, info->sechdrs, mod);
    > + err = module_finalize(info->hdr, info->sechdrs, mod);
    > + if (err < 0)

    if (err < 0 && is_livepatch_module(mod))

    > + free_module_elf(mod);
    > +
    > + return err;
    > }

    Also we need to free the copied stuff in load_module() when
    anything called after post_relocation() fails. I think
    that the following would work:

    --- a/kernel/module.c
    +++ b/kernel/module.c
    @@ -3823,6 +3823,8 @@ static int load_module(struct load_info *info, const char __user *uargs,
    kfree(mod->args);
    free_arch_cleanup:
    module_arch_cleanup(mod);
    + if (is_livepatch_module(mod))
    + free_module_elf(mod);
    free_modinfo:
    free_modinfo(mod);
    free_unload:

    But I suggest to just move copy_module_elf() up and keep
    calling it from load_module() directly. It would make
    the error handling more clear.

    Best Regards,
    Petr

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