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SubjectRe: [RFC PATCH v4 2/6] module: preserve Elf information for livepatch modules
On Wed, Feb 03, 2016 at 08:11:07PM -0500, Jessica Yu wrote:
> 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.

This patch didn't apply clean to linux-next/master. I didn't
investigate why, but maybe it depends on the other patch set which
removes the notifiers? (If so, that should be mentioned in the cover
letter.)

A couple of minor comments below...

> Signed-off-by: Jessica Yu <jeyu@redhat.com>
> ---
> include/linux/module.h | 25 ++++++++++
> kernel/module.c | 133 ++++++++++++++++++++++++++++++++++++++++++++++---
> 2 files changed, 151 insertions(+), 7 deletions(-)
>
> diff --git a/include/linux/module.h b/include/linux/module.h
> index 4560d8f..58e6200 100644
> --- a/include/linux/module.h
> +++ b/include/linux/module.h
> @@ -324,6 +324,15 @@ struct module_layout {
> #define __module_layout_align
> #endif
>
> +#ifdef CONFIG_LIVEPATCH
> +struct klp_modinfo {
> + Elf_Ehdr hdr;
> + Elf_Shdr *sechdrs;
> + char *secstrings;
> + unsigned int symndx;
> +};
> +#endif
> +
> struct module {
> enum module_state state;
>
> @@ -455,7 +464,11 @@ 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
> @@ -629,6 +642,18 @@ 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 71c77ed..9c16eb2 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -1970,6 +1970,82 @@ 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 = 0;
> +
> + size = sizeof(*mod->klp_info);
> + mod->klp_info = kmalloc(size, GFP_KERNEL);
> + if (mod->klp_info == NULL)
> + return -ENOMEM;
> +
> + /* Elf header */
> + size = sizeof(Elf_Ehdr);
> + memcpy(&mod->klp_info->hdr, info->hdr, size);
> +
> + /* Elf section header table */
> + size = sizeof(Elf_Shdr) * 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_symtab is a complete copy
> + * of the original symbol table. Adjust sh_addr to point
> + * to core_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_symtab;
> +
> + return ret;
> +
> +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);
> @@ -2008,6 +2084,10 @@ static void free_module(struct module *mod)
> /* Free any allocated parameters. */
> destroy_params(mod->kp, mod->num_kp);
>
> + /* Free Elf information if it was saved */
> + if (is_livepatch_module(mod))
> + free_module_elf(mod);
> +

I think this code is self-evident, so the comment isn't necessary.


> /* Now we can delete it from the lists */
> mutex_lock(&module_mutex);
> /* Unlink carefully: kallsyms could be walking list. */
> @@ -2123,6 +2203,10 @@ 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. */
> @@ -2171,6 +2255,10 @@ 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);
> @@ -2466,7 +2554,7 @@ 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;
> @@ -2509,7 +2597,7 @@ static void add_kallsyms(struct module *mod, const struct load_info *info)
> mod->core_strtab = s = mod->core_layout.base + info->stroffs;
> src = mod->symtab;
> for (ndst = i = 0; i < mod->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];
> @@ -2676,6 +2764,23 @@ static int copy_module_from_user(const void __user *umod, unsigned long len,
> 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"))
> + return -ENOEXEC;
> +
> + return 0;
> +}
> +#endif /* CONFIG_LIVEPATCH */
> +
> /* Sets info->hdr and info->len. */
> static int copy_module_from_fd(int fd, struct load_info *info)
> {
> @@ -2859,6 +2964,10 @@ 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"));
>
> @@ -3222,6 +3331,12 @@ static noinline int do_init_module(struct module *mod)
> */
> current->flags &= ~PF_USED_ASYNC;
>
> +#ifdef CONFIG_KALLSYMS
> + /* Make symtab and strtab available prior to module init call */
> + mod->num_symtab = mod->core_num_syms;
> + mod->symtab = mod->core_symtab;
> + mod->strtab = mod->core_strtab;
> +#endif
> do_mod_ctors(mod);
> /* Start the module */
> if (mod->init != NULL)
> @@ -3266,11 +3381,6 @@ static noinline int do_init_module(struct module *mod)
> /* Drop initial reference. */
> module_put(mod);
> trim_init_extable(mod);
> -#ifdef CONFIG_KALLSYMS
> - mod->num_symtab = mod->core_num_syms;
> - mod->symtab = mod->core_symtab;
> - mod->strtab = mod->core_strtab;
> -#endif
> mod_tree_remove_init(mod);
> disable_ro_nx(&mod->init_layout);
> module_arch_freeing_init(mod);
> @@ -3522,6 +3632,13 @@ static int load_module(struct load_info *info, const char __user *uargs,
> if (err < 0)
> goto bug_cleanup;
>
> + /* For livepatch modules, save Elf info from load_info struct */
> + if (is_livepatch_module(mod)) {
> + err = copy_module_elf(mod, info);
> + if (err < 0)
> + goto sysfs_cleanup;
> + }
> +

Same here, unecessary comment IMO.

> /* Get rid of temporary copy. */
> free_copy(info);
>
> @@ -3530,6 +3647,8 @@ static int load_module(struct load_info *info, const char __user *uargs,
>
> return do_init_module(mod);
>
> + sysfs_cleanup:
> + mod_sysfs_teardown(mod);
> bug_cleanup:
> /* module_bug_cleanup needs module_mutex protection */
> mutex_lock(&module_mutex);
> --
> 2.4.3
>

--
Josh

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