Re: [PATCH 2/2] module: Add module name to modinfo

[Jessica Yu]

+++ Kees Cook [12/04/17 16:16 -0700]:
> Accessing the mod structure (e.g. for mod->name) prior to having completed
> check_modstruct_version() can result in writing garbage to the error logs
> if the layout of the mod structure loaded from disk doesn't match the
> running kernel's mod structure layout. This kind of mismatch will become
> much more likely if a kernel is built with different randomization seed
> for the struct layout randomization plugin.
>
> Instead, add and use a new modinfo string for logging the module name.
>
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
> ---
> kernel/module.c       | 21 ++++++++++++++-------
> scripts/mod/modpost.c |  1 +
> 2 files changed, 15 insertions(+), 7 deletions(-)
>
> diff --git a/kernel/module.c b/kernel/module.c
> index ed6cf2367217..ed4a399174ba 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -299,6 +299,7 @@ int unregister_module_notifier(struct notifier_block *nb)
> EXPORT_SYMBOL(unregister_module_notifier);
>
> struct load_info {
> +	char *name;
> 	Elf_Ehdr *hdr;
> 	unsigned long len;
> 	Elf_Shdr *sechdrs;
> @@ -1297,12 +1298,12 @@ static int check_version(const struct load_info *info,
> 	}
>
> 	/* Broken toolchain. Warn once, then let it go.. */
> -	pr_warn_once("%s: no symbol version for %s\n", mod->name, symname);
> +	pr_warn_once("%s: no symbol version for %s\n", info->name, symname);
> 	return 1;
>
> bad_version:
> 	pr_warn("%s: disagrees about version of symbol %s\n",
> -	       mod->name, symname);
> +	       info->name, symname);
> 	return 0;
> }
>
> @@ -2892,9 +2893,15 @@ static int rewrite_section_headers(struct load_info *info, int flags)
> 		info->index.vers = 0; /* Pretend no __versions section! */
> 	else
> 		info->index.vers = find_sec(info, "__versions");
> +	info->sechdrs[info->index.vers].sh_flags &= ~(unsigned long)SHF_ALLOC;
> +
> 	info->index.info = find_sec(info, ".modinfo");
> +	if (!info->index.info)
> +		info->name = "unknown";
> +	else
> +		info->name = get_modinfo(info, "name");

Hm, if we attempt to load an old module without the new name field
(i.e. all modules currently), we'll end up printing "(null)" for all
the prints that use info->name. Maybe we can fall back to mod->name if
the name field isn't there and the kernel wasn't compiled with the
randstruct plugin?

> 	info->sechdrs[info->index.info].sh_flags &= ~(unsigned long)SHF_ALLOC;
> -	info->sechdrs[info->index.vers].sh_flags &= ~(unsigned long)SHF_ALLOC;
> +
> 	return 0;
> }
>
> @@ -2934,14 +2941,14 @@ static struct module *setup_load_info(struct load_info *info, int flags)
>
> 	info->index.mod = find_sec(info, ".gnu.linkonce.this_module");
> 	if (!info->index.mod) {
> -		pr_warn("No module found in object\n");
> +		pr_warn("%s: No module found in object\n", info->name);
> 		return ERR_PTR(-ENOEXEC);
> 	}
> 	/* This is temporary: point mod into copy of data. */
> 	mod = (void *)info->sechdrs[info->index.mod].sh_addr;
>
> 	if (info->index.sym == 0) {
> -		pr_warn("%s: module has no symbols (stripped?)\n", mod->name);
> +		pr_warn("%s: module has no symbols (stripped?)\n", info->name);
> 		return ERR_PTR(-ENOEXEC);
> 	}
>
> @@ -2969,7 +2976,7 @@ static int check_modinfo(struct module *mod, struct load_info *info, int flags)
> 			return err;
> 	} else if (!same_magic(modmagic, vermagic, info->index.vers)) {
> 		pr_err("%s: version magic '%s' should be '%s'\n",
> -		       mod->name, modmagic, vermagic);
> +		       info->name, modmagic, vermagic);
> 		return -ENOEXEC;
> 	}

Maybe we want to use info->name for the blacklisted() check as well (see
layout_and_allocate()).

> @@ -3622,7 +3629,7 @@ static int load_module(struct load_info *info, const char __user *uargs,
> 	if (!mod->sig_ok) {
> 		pr_notice_once("%s: module verification failed: signature "
> 			       "and/or required key missing - tainting "
> -			       "kernel\n", mod->name);
> +			       "kernel\n", info->name);
> 		add_taint_module(mod, TAINT_UNSIGNED_MODULE, LOCKDEP_STILL_OK);
> 	}

Do we still need to use info->name here? At this point we're done with
layout_and_allocate(), plus the modstruct check and vermagic check, and mod
should be pointing to its new place in memory.

> #endif
> diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
> index 30d752a4a6a6..48397feb08fb 100644
> --- a/scripts/mod/modpost.c
> +++ b/scripts/mod/modpost.c
> @@ -2126,6 +2126,7 @@ static void add_header(struct buffer *b, struct module *mod)
> 	buf_printf(b, "#include <linux/compiler.h>\n");
> 	buf_printf(b, "\n");
> 	buf_printf(b, "MODULE_INFO(vermagic, VERMAGIC_STRING);\n");
> +	buf_printf(b, "MODULE_INFO(name, KBUILD_MODNAME);\n");
> 	buf_printf(b, "\n");
> 	buf_printf(b, "__visible struct module __this_module\n");
> 	buf_printf(b, "__attribute__((section(\".gnu.linkonce.this_module\"))) = {\n");
> --
> 2.7.4