Re: [PATCH v6 2/5] module: preserve Elf information for livepatch modules

Rusty Russell
2016-04-01T00:22:27Z

Jessica Yu <jeyu@redhat.com> writes:
> For livepatch modules, copy Elf section, symbol, and string information
> from the load_info struct in the module loader. Persist copies of the
> original symbol table and string table.
>
> Livepatch manages its own relocation sections in order to reuse module
> loader code to write relocations. Livepatch modules must preserve Elf
> information such as section indices in order to apply livepatch relocation
> sections using the module loader's apply_relocate_add() function.
>
> In order to apply livepatch relocation sections, livepatch modules must
> keep a complete copy of their original symbol table in memory. Normally, a
> stripped down copy of a module's symbol table (containing only "core"
> symbols) is made available through module->core_symtab. But for livepatch
> modules, the symbol table copied into memory on module load must be exactly
> the same as the symbol table produced when the patch module was compiled.
> This is because the relocations in each livepatch relocation section refer
> to their respective symbols with their symbol indices, and the original
> symbol indices (and thus the symtab ordering) must be preserved in order
> for apply_relocate_add() to find the right symbol.
>
> Signed-off-by: Jessica Yu <jeyu@redhat.com>
> Reviewed-by: Miroslav Benes <mbenes@suse.cz>
> ---
> include/linux/module.h | 25 ++++++++++
> kernel/module.c | 125 +++++++++++++++++++++++++++++++++++++++++++++++--
> 2 files changed, 147 insertions(+), 3 deletions(-)

Acked-by: Rusty Russell <rusty@rustcorp.com.au>

(I guess that takes precedence over "Reviewed-by", which I did too).

Thanks,
Rusty.

> diff --git a/include/linux/module.h b/include/linux/module.h
> index 2bb0c30..3daf2b3 100644
> --- a/include/linux/module.h
> +++ b/include/linux/module.h
> @@ -330,6 +330,15 @@ struct mod_kallsyms {
> char *strtab;
> };
>
> +#ifdef CONFIG_LIVEPATCH
> +struct klp_modinfo {
> + Elf_Ehdr hdr;
> + Elf_Shdr *sechdrs;
> + char *secstrings;
> + unsigned int symndx;
> +};
> +#endif
> +
> struct module {
> enum module_state state;
>
> @@ -456,7 +465,11 @@ struct module {
> #endif
>
> #ifdef CONFIG_LIVEPATCH
> + bool klp; /* Is this a livepatch module? */
> bool klp_alive;
> +
> + /* Elf information */
> + struct klp_modinfo *klp_info;
> #endif
>
> #ifdef CONFIG_MODULE_UNLOAD
> @@ -630,6 +643,18 @@ static inline bool module_requested_async_probing(struct module *module)
> return module && module->async_probe_requested;
> }
>
> +#ifdef CONFIG_LIVEPATCH
> +static inline bool is_livepatch_module(struct module *mod)
> +{
> + return mod->klp;
> +}
> +#else /* !CONFIG_LIVEPATCH */
> +static inline bool is_livepatch_module(struct module *mod)
> +{
> + return false;
> +}
> +#endif /* CONFIG_LIVEPATCH */
> +
> #else /* !CONFIG_MODULES... */
>
> /* Given an address, look for it in the exception tables. */
> diff --git a/kernel/module.c b/kernel/module.c
> index 041200c..5f71aa6 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -1973,6 +1973,83 @@ static void module_enable_nx(const struct module *mod) { }
> static void module_disable_nx(const struct module *mod) { }
> #endif
>
> +#ifdef CONFIG_LIVEPATCH
> +/*
> + * Persist Elf information about a module. Copy the Elf header,
> + * section header table, section string table, and symtab section
> + * index from info to mod->klp_info.
> + */
> +static int copy_module_elf(struct module *mod, struct load_info *info)
> +{
> + unsigned int size, symndx;
> + int ret;
> +
> + size = sizeof(*mod->klp_info);
> + mod->klp_info = kmalloc(size, GFP_KERNEL);
> + if (mod->klp_info == NULL)
> + return -ENOMEM;
> +
> + /* Elf header */
> + size = sizeof(mod->klp_info->hdr);
> + memcpy(&mod->klp_info->hdr, info->hdr, size);
> +
> + /* Elf section header table */
> + size = sizeof(*info->sechdrs) * info->hdr->e_shnum;
> + mod->klp_info->sechdrs = kmalloc(size, GFP_KERNEL);
> + if (mod->klp_info->sechdrs == NULL) {
> + ret = -ENOMEM;
> + goto free_info;
> + }
> + memcpy(mod->klp_info->sechdrs, info->sechdrs, size);
> +
> + /* Elf section name string table */
> + size = info->sechdrs[info->hdr->e_shstrndx].sh_size;
> + mod->klp_info->secstrings = kmalloc(size, GFP_KERNEL);
> + if (mod->klp_info->secstrings == NULL) {
> + ret = -ENOMEM;
> + goto free_sechdrs;
> + }
> + memcpy(mod->klp_info->secstrings, info->secstrings, size);
> +
> + /* Elf symbol section index */
> + symndx = info->index.sym;
> + mod->klp_info->symndx = symndx;
> +
> + /*
> + * For livepatch modules, core_kallsyms.symtab is a complete
> + * copy of the original symbol table. Adjust sh_addr to point
> + * to core_kallsyms.symtab since the copy of the symtab in module
> + * init memory is freed at the end of do_init_module().
> + */
> + mod->klp_info->sechdrs[symndx].sh_addr = \
> + (unsigned long) mod->core_kallsyms.symtab;
> +
> + return 0;
> +
> +free_sechdrs:
> + kfree(mod->klp_info->sechdrs);
> +free_info:
> + kfree(mod->klp_info);
> + return ret;
> +}
> +
> +static void free_module_elf(struct module *mod)
> +{
> + kfree(mod->klp_info->sechdrs);
> + kfree(mod->klp_info->secstrings);
> + kfree(mod->klp_info);
> +}
> +#else /* !CONFIG_LIVEPATCH */
> +static int copy_module_elf(struct module *mod, struct load_info *info)
> +{
> + return 0;
> +}
> +
> +static void free_module_elf(struct module *mod)
> +{
> +}
> +#endif /* CONFIG_LIVEPATCH */
> +
> void __weak module_memfree(void *module_region)
> {
> vfree(module_region);
> @@ -2011,6 +2088,9 @@ static void free_module(struct module *mod)
> /* Free any allocated parameters. */
> destroy_params(mod->kp, mod->num_kp);
>
> + if (is_livepatch_module(mod))
> + free_module_elf(mod);
> +
> /* Now we can delete it from the lists */
> mutex_lock(&module_mutex);
> /* Unlink carefully: kallsyms could be walking list. */
> @@ -2126,6 +2206,10 @@ static int simplify_symbols(struct module *mod, const struct load_info *info)
> (long)sym[i].st_value);
> break;
>
> + case SHN_LIVEPATCH:
> + /* Livepatch symbols are resolved by livepatch */
> + break;
> +
> case SHN_UNDEF:
> ksym = resolve_symbol_wait(mod, info, name);
> /* Ok if resolved. */
> @@ -2174,6 +2258,10 @@ 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 = apply_relocate(info->sechdrs, info->strtab,
> info->index.sym, i, mod);
> @@ -2469,7 +2557,7 @@ static void layout_symtab(struct module *mod, struct load_info *info)
>
> /* Compute total space required for the core symbols' strtab. */
> for (ndst = i = 0; i < nsrc; i++) {
> - if (i == 0 ||
> + if (i == 0 || is_livepatch_module(mod) ||
> is_core_symbol(src+i, info->sechdrs, info->hdr->e_shnum,
> info->index.pcpu)) {
> strtab_size += strlen(&info->strtab[src[i].st_name])+1;
> @@ -2528,7 +2616,7 @@ static void add_kallsyms(struct module *mod, const struct load_info *info)
> mod->core_kallsyms.strtab = s = mod->core_layout.base + info->stroffs;
> src = mod->kallsyms->symtab;
> for (ndst = i = 0; i < mod->kallsyms->num_symtab; i++) {
> - if (i == 0 ||
> + if (i == 0 || is_livepatch_module(mod) ||
> is_core_symbol(src+i, info->sechdrs, info->hdr->e_shnum,
> info->index.pcpu)) {
> dst[ndst] = src[i];
> @@ -2667,6 +2755,26 @@ static int copy_chunked_from_user(void *dst, const void __user *usrc, unsigned l
> return 0;
> }
>
> +#ifdef CONFIG_LIVEPATCH
> +static int find_livepatch_modinfo(struct module *mod, struct load_info *info)
> +{
> + mod->klp = get_modinfo(info, "livepatch") ? true : false;
> +
> + return 0;
> +}
> +#else /* !CONFIG_LIVEPATCH */
> +static int find_livepatch_modinfo(struct module *mod, struct load_info *info)
> +{
> + if (get_modinfo(info, "livepatch")) {
> + pr_err("%s: module is marked as livepatch module, but livepatch support is disabled",
> + mod->name);
> + return -ENOEXEC;
> + }
> +
> + return 0;
> +}
> +#endif /* CONFIG_LIVEPATCH */
> +
> /* Sets info->hdr and info->len. */
> static int copy_module_from_user(const void __user *umod, unsigned long len,
> struct load_info *info)
> @@ -2821,6 +2929,10 @@ static int check_modinfo(struct module *mod, struct load_info *info, int flags)
> "is unknown, you have been warned.\n", mod->name);
> }
>
> + err = find_livepatch_modinfo(mod, info);
> + if (err)
> + return err;
> +
> /* Set up license info based on the info section */
> set_license(mod, get_modinfo(info, "license"));
>
> @@ -3494,6 +3606,12 @@ static int load_module(struct load_info *info, const char __user *uargs,
> if (err < 0)
> goto coming_cleanup;
>
> + if (is_livepatch_module(mod)) {
> + err = copy_module_elf(mod, info);
> + if (err < 0)
> + goto sysfs_cleanup;
> + }
> +
> /* Get rid of temporary copy. */
> free_copy(info);
>
> @@ -3502,11 +3620,12 @@ static int load_module(struct load_info *info, const char __user *uargs,
>
> return do_init_module(mod);
>
> + sysfs_cleanup:
> + mod_sysfs_teardown(mod);
> coming_cleanup:
> blocking_notifier_call_chain(&module_notify_list,
> MODULE_STATE_GOING, mod);
> klp_module_going(mod);
> -
> bug_cleanup:
> /* module_bug_cleanup needs module_mutex protection */
> mutex_lock(&module_mutex);
> --
> 2.4.3