On Wed, Mar 16, 2016 at 03:47:04PM -0400, 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.
>
> Signed-off-by: Jessica Yu <jeyu@xxxxxxxxxx>
> ---
> include/linux/module.h | 25 ++++++++++
> kernel/module.c | 123 ++++++++++++++++++++++++++++++++++++++++++++++++-
> 2 files changed, 146 insertions(+), 2 deletions(-)
>
> 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 87cfeb2..80b7fd9 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -1971,6 +1971,82 @@ 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;
> +
> + 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;
nit: The 'symndx' local variable is superfluous.
> +
> + /*
> + * For livepatch modules, core_symtab is a complete copy
s/core_symtab/core_kallsyms.symtab/ ?
> + * 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_kallsyms.symtab;
--
Josh
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