Re: [PATCH 2/6] module: add support for symbol namespaces.

[Lucas De Marchi <lucas.de.marchi@gmail.com>]

On Wed, Jul 25, 2018 at 8:55 AM Jessica Yu <jeyu@kernel.org> wrote:
>
> +++ Martijn Coenen [24/07/18 09:56 +0200]:
> >I did find an issue with my approach:
> >
> >On Mon, Jul 16, 2018 at 2:21 PM, Martijn Coenen <maco@android.com> wrote:
> >> The ELF symbols are renamed to include the namespace with an asm label;
> >> for example, symbol 'usb_stor_suspend' in namespace USB_STORAGE becomes
> >> 'usb_stor_suspend.USB_STORAGE'.  This allows modpost to do namespace
> >> checking, without having to go through all the effort of parsing ELF and
> >> reloction records just to get to the struct kernel_symbols.
> >
> >depmod doesn't like this: if namespaced symbols are built-in to the
> >kernel, they will appear as 'symbol.NS' in the symbol table, whereas
> >modules using those symbols just depend on 'symbol'. This will cause
> >depmod to warn about unknown symbols. I didn't find this previously
> >because all the exports/imports I tested were done from modules
> >themselves.
> >
> >One way to deal with it is to change depmod, but it looks like it
> >hasn't been changed in ages, and it would also introduce a dependency

this might be because you are looking to the wrong project
(module-init-tools) rather than kmod that replaced it some years ago?

> >on userspaces to update it to avoid these warnings. So, we'd have to
> >encode the symbol namespace information in another way for modpost to
> >use. I could just write a separate post-processing tool (much like
> >genksyms), or perhaps encode the information in a discardable section.
> >Any other suggestions welcome.
>
> This seems to be because depmod uses System.map as a source for kernel
> symbols and scans for only the ones prefixed with "__ksymtab" to find
> the exported ones - and those happen to use the '.' to mark the
> namespace it belongs to. It strips that prefix and uses the remainder
> as the actual symbol name. To fix that it'd have to strip the
> namespace suffix in the symbol name as well.
>
> Just scanning the depmod source code, it seems really trivial to just
> have depmod accommodate the new symbol name format. Adding Lucas (kmod
> maintainer) to CC.

Yep, that would be easy and allow depmod to be backward compatible
since we would do nothing if the symbol doesn't have the suffix.
As for dependency on a new version, this seems trivial enough to be
backported to previous releases used on distros so even if they are
not rolling they would get a compatible depmod.

CC'ing linux-modules@vger.kernel.org to keep track of this there


thanks
Lucas De Marchi

>
> Thanks,
>
> Jessica
>
> >
> >>
> >> On x86_64 I saw no difference in binary size (compression), but at
> >> runtime this will require a word of memory per export to hold the
> >> namespace. An alternative could be to store namespaced symbols in their
> >> own section and use a separate 'struct namespaced_kernel_symbol' for
> >> that section, at the cost of making the module loader more complex.
> >>
> >> Signed-off-by: Martijn Coenen <maco@android.com>
> >> ---
> >>  include/asm-generic/export.h |  2 +-
> >>  include/linux/export.h       | 83 +++++++++++++++++++++++++++---------
> >>  include/linux/module.h       | 13 ++++++
> >>  kernel/module.c              | 79 ++++++++++++++++++++++++++++++++++
> >>  4 files changed, 156 insertions(+), 21 deletions(-)
> >>
> >> diff --git a/include/asm-generic/export.h b/include/asm-generic/export.h
> >> index 68efb950a918..4c3d1afb702f 100644
> >> --- a/include/asm-generic/export.h
> >> +++ b/include/asm-generic/export.h
> >> @@ -29,7 +29,7 @@
> >>         .section ___ksymtab\sec+\name,"a"
> >>         .balign KSYM_ALIGN
> >>  __ksymtab_\name:
> >> -       __put \val, __kstrtab_\name
> >> +       __put \val, __kstrtab_\name, 0
> >>         .previous
> >>         .section __ksymtab_strings,"a"
> >>  __kstrtab_\name:
> >> diff --git a/include/linux/export.h b/include/linux/export.h
> >> index ad6b8e697b27..9f6e70eeb85f 100644
> >> --- a/include/linux/export.h
> >> +++ b/include/linux/export.h
> >> @@ -22,6 +22,11 @@ struct kernel_symbol
> >>  {
> >>         unsigned long value;
> >>         const char *name;
> >> +       const char *namespace;
> >> +};
> >> +
> >> +struct namespace_import {
> >> +       const char *namespace;
> >>  };
> >>
> >>  #ifdef MODULE
> >> @@ -54,18 +59,28 @@ extern struct module __this_module;
> >>  #define __CRC_SYMBOL(sym, sec)
> >>  #endif
> >>
> >> +#define NS_SEPARATOR "."
> >> +
> >> +#define MODULE_IMPORT_NS(ns)                                           \
> >> +       static const struct namespace_import __knsimport_##ns           \
> >> +       asm("__knsimport_" #ns)                                         \
> >> +       __attribute__((section("__knsimport"), used))                   \
> >> +       = { #ns }
> >> +
> >>  /* For every exported symbol, place a struct in the __ksymtab section */
> >> -#define ___EXPORT_SYMBOL(sym, sec)                                     \
> >> +#define ___EXPORT_SYMBOL(sym, sec, ns, nspost, nspost2)                        \
> >>         extern typeof(sym) sym;                                         \
> >>         __CRC_SYMBOL(sym, sec)                                          \
> >> -       static const char __kstrtab_##sym[]                             \
> >> +       static const char __kstrtab_##sym##nspost[]                     \
> >>         __attribute__((section("__ksymtab_strings"), aligned(1)))       \
> >>         = #sym;                                                         \
> >> -       static const struct kernel_symbol __ksymtab_##sym               \
> >> +       static const struct kernel_symbol __ksymtab_##sym##nspost       \
> >> +       asm("__ksymtab_" #sym nspost2)                                  \
> >>         __used                                                          \
> >> -       __attribute__((section("___ksymtab" sec "+" #sym), used))       \
> >> +       __attribute__((section("___ksymtab" sec "+" #sym #nspost)))     \
> >> +       __attribute__((used))                                           \
> >>         __attribute__((aligned(sizeof(void *))))                        \
> >> -       = { (unsigned long)&sym, __kstrtab_##sym }
> >> +       = { (unsigned long)&sym, __kstrtab_##sym##nspost, ns }
> >>
> >>  #if defined(__KSYM_DEPS__)
> >>
> >> @@ -76,52 +91,80 @@ extern struct module __this_module;
> >>   * system filters out from the preprocessor output (see ksym_dep_filter
> >>   * in scripts/Kbuild.include).
> >>   */
> >> -#define __EXPORT_SYMBOL(sym, sec)      === __KSYM_##sym ===
> >> +#define __EXPORT_SYMBOL(sym, sec, ns, nspost, nspost2) === __KSYM_##sym ===
> >>
> >>  #elif defined(CONFIG_TRIM_UNUSED_KSYMS)
> >>
> >>  #include <generated/autoksyms.h>
> >>
> >> -#define __EXPORT_SYMBOL(sym, sec)                              \
> >> -       __cond_export_sym(sym, sec, __is_defined(__KSYM_##sym))
> >> -#define __cond_export_sym(sym, sec, conf)                      \
> >> -       ___cond_export_sym(sym, sec, conf)
> >> -#define ___cond_export_sym(sym, sec, enabled)                  \
> >> -       __cond_export_sym_##enabled(sym, sec)
> >> -#define __cond_export_sym_1(sym, sec) ___EXPORT_SYMBOL(sym, sec)
> >> -#define __cond_export_sym_0(sym, sec) /* nothing */
> >> +#define __EXPORT_SYMBOL(sym, sec, ns, nspost, nspost2)                 \
> >> +       __cond_export_sym(sym, sec, ns, nspost, nspost2,                \
> >> +                         __is_defined(__KSYM_##sym))
> >> +#define __cond_export_sym(sym, sec, ns, nspost, nspost2, conf)         \
> >> +       ___cond_export_sym(sym, sec, ns, nspost, nspost2, conf)
> >> +#define ___cond_export_sym(sym, sec, ns, nspost, nspost2, enabled)     \
> >> +       __cond_export_sym_##enabled(sym, sec, ns, nspost, nspost2)
> >> +#define __cond_export_sym_1(sym, sec, ns, nspost, nspost2)             \
> >> +       ___EXPORT_SYMBOL(sym, sec, ns, nspost, nspost2)
> >> +#define __cond_export_sym_0(sym, sec, ns, nspost, nspost2) /* nothing */
> >>
> >>  #else
> >>  #define __EXPORT_SYMBOL ___EXPORT_SYMBOL
> >>  #endif
> >>
> >>  #define EXPORT_SYMBOL(sym)                                     \
> >> -       __EXPORT_SYMBOL(sym, "")
> >> +       __EXPORT_SYMBOL(sym, "", NULL, ,)
> >>
> >>  #define EXPORT_SYMBOL_GPL(sym)                                 \
> >> -       __EXPORT_SYMBOL(sym, "_gpl")
> >> +       __EXPORT_SYMBOL(sym, "_gpl", NULL, ,)
> >>
> >>  #define EXPORT_SYMBOL_GPL_FUTURE(sym)                          \
> >> -       __EXPORT_SYMBOL(sym, "_gpl_future")
> >> +       __EXPORT_SYMBOL(sym, "_gpl_future", NULL, ,)
> >> +
> >> +#define EXPORT_SYMBOL_NS(sym, ns)                               \
> >> +       __EXPORT_SYMBOL(sym, "", #ns, __##ns, NS_SEPARATOR #ns)
> >> +
> >> +#define EXPORT_SYMBOL_NS_GPL(sym, ns)                               \
> >> +       __EXPORT_SYMBOL(sym, "_gpl", #ns, __##ns, NS_SEPARATOR #ns)
> >>
> >>  #ifdef CONFIG_UNUSED_SYMBOLS
> >> -#define EXPORT_UNUSED_SYMBOL(sym) __EXPORT_SYMBOL(sym, "_unused")
> >> -#define EXPORT_UNUSED_SYMBOL_GPL(sym) __EXPORT_SYMBOL(sym, "_unused_gpl")
> >> +#define EXPORT_UNUSED_SYMBOL(sym) __EXPORT_SYMBOL(sym, "_unused", , ,)
> >> +#define EXPORT_UNUSED_SYMBOL_GPL(sym) __EXPORT_SYMBOL(sym, "_unused_gpl", , ,)
> >>  #else
> >>  #define EXPORT_UNUSED_SYMBOL(sym)
> >>  #define EXPORT_UNUSED_SYMBOL_GPL(sym)
> >>  #endif
> >>
> >> -#endif /* __GENKSYMS__ */
> >> +#endif /* __KERNEL__ && !__GENKSYMS__ */
> >> +
> >> +#if defined(__GENKSYMS__)
> >> +/*
> >> + * When we're running genksyms, ignore the namespace and make the _NS
> >> + * variants look like the normal ones. There are two reasons for this:
> >> + * 1) In the normal definition of EXPORT_SYMBOL_NS, the 'ns' macro
> >> + *    argument is itself not expanded because it's always tokenized or
> >> + *    concatenated; but when running genksyms, a blank definition of the
> >> + *    macro does allow the argument to be expanded; if a namespace
> >> + *    happens to collide with a #define, this can cause issues.
> >> + * 2) There's no need to modify genksyms to deal with the _NS variants
> >> + */
> >> +#define EXPORT_SYMBOL_NS(sym, ns)                              \
> >> +       EXPORT_SYMBOL(sym)
> >> +#define EXPORT_SYMBOL_NS_GPL(sym, ns)                          \
> >> +       EXPORT_SYMBOL_GPL(sym)
> >> +#endif
> >>
> >>  #else /* !CONFIG_MODULES... */
> >>
> >>  #define EXPORT_SYMBOL(sym)
> >> +#define EXPORT_SYMBOL_NS(sym, ns)
> >> +#define EXPORT_SYMBOL_NS_GPL(sym, ns)
> >>  #define EXPORT_SYMBOL_GPL(sym)
> >>  #define EXPORT_SYMBOL_GPL_FUTURE(sym)
> >>  #define EXPORT_UNUSED_SYMBOL(sym)
> >>  #define EXPORT_UNUSED_SYMBOL_GPL(sym)
> >>
> >> +#define MODULE_IMPORT_NS(ns)
> >>  #endif /* CONFIG_MODULES */
> >>  #endif /* !__ASSEMBLY__ */
> >>
> >> diff --git a/include/linux/module.h b/include/linux/module.h
> >> index d44df9b2c131..afab4e8fa188 100644
> >> --- a/include/linux/module.h
> >> +++ b/include/linux/module.h
> >> @@ -268,6 +268,12 @@ void *__symbol_get(const char *symbol);
> >>  void *__symbol_get_gpl(const char *symbol);
> >>  #define symbol_get(x) ((typeof(&x))(__symbol_get(VMLINUX_SYMBOL_STR(x))))
> >>
> >> +/* namespace dependencies of the module */
> >> +struct module_ns_dep {
> >> +       struct list_head ns_dep;
> >> +       const char *namespace;
> >> +};
> >> +
> >>  /* modules using other modules: kdb wants to see this. */
> >>  struct module_use {
> >>         struct list_head source_list;
> >> @@ -359,6 +365,13 @@ struct module {
> >>         const struct kernel_symbol *gpl_syms;
> >>         const s32 *gpl_crcs;
> >>
> >> +       /* Namespace imports */
> >> +       unsigned int num_ns_imports;
> >> +       const struct namespace_import *ns_imports;
> >> +
> >> +       /* Namespace dependencies */
> >> +       struct list_head ns_dependencies;
> >> +
> >>  #ifdef CONFIG_UNUSED_SYMBOLS
> >>         /* unused exported symbols. */
> >>         const struct kernel_symbol *unused_syms;
> >> diff --git a/kernel/module.c b/kernel/module.c
> >> index f475f30eed8c..63de0fe849f9 100644
> >> --- a/kernel/module.c
> >> +++ b/kernel/module.c
> >> @@ -1166,6 +1166,51 @@ static inline int module_unload_init(struct module *mod)
> >>  }
> >>  #endif /* CONFIG_MODULE_UNLOAD */
> >>
> >> +static bool module_has_ns_dependency(struct module *mod, const char *ns)
> >> +{
> >> +       struct module_ns_dep *ns_dep;
> >> +
> >> +       list_for_each_entry(ns_dep, &mod->ns_dependencies, ns_dep) {
> >> +               if (strcmp(ns_dep->namespace, ns) == 0)
> >> +                       return true;
> >> +       }
> >> +
> >> +       return false;
> >> +}
> >> +
> >> +static int add_module_ns_dependency(struct module *mod, const char *ns)
> >> +{
> >> +       struct module_ns_dep *ns_dep;
> >> +
> >> +       if (module_has_ns_dependency(mod, ns))
> >> +               return 0;
> >> +
> >> +       ns_dep = kmalloc(sizeof(*ns_dep), GFP_ATOMIC);
> >> +       if (!ns_dep)
> >> +               return -ENOMEM;
> >> +
> >> +       ns_dep->namespace = ns;
> >> +
> >> +       list_add(&ns_dep->ns_dep, &mod->ns_dependencies);
> >> +
> >> +       return 0;
> >> +}
> >> +
> >> +static bool module_imports_ns(struct module *mod, const char *ns)
> >> +{
> >> +       size_t i;
> >> +
> >> +       if (!ns)
> >> +               return true;
> >> +
> >> +       for (i = 0; i < mod->num_ns_imports; ++i) {
> >> +               if (!strcmp(mod->ns_imports[i].namespace, ns))
> >> +                       return true;
> >> +       }
> >> +
> >> +       return false;
> >> +}
> >> +
> >>  static size_t module_flags_taint(struct module *mod, char *buf)
> >>  {
> >>         size_t l = 0;
> >> @@ -1415,6 +1460,18 @@ static const struct kernel_symbol *resolve_symbol(struct module *mod,
> >>                 goto getname;
> >>         }
> >>
> >> +       /*
> >> +        * We can't yet verify that the module actually imports this
> >> +        * namespace, because the imports themselves are only available
> >> +        * after processing the symbol table and doing relocation; so
> >> +        * instead just record the dependency and check later.
> >> +        */
> >> +       if (sym->namespace) {
> >> +               err = add_module_ns_dependency(mod, sym->namespace);
> >> +               if (err)
> >> +                       sym = ERR_PTR(err);
> >> +       }
> >> +
> >>  getname:
> >>         /* We must make copy under the lock if we failed to get ref. */
> >>         strncpy(ownername, module_name(owner), MODULE_NAME_LEN);
> >> @@ -3061,6 +3118,11 @@ static int find_module_sections(struct module *mod, struct load_info *info)
> >>                                      sizeof(*mod->gpl_syms),
> >>                                      &mod->num_gpl_syms);
> >>         mod->gpl_crcs = section_addr(info, "__kcrctab_gpl");
> >> +
> >> +       mod->ns_imports = section_objs(info, "__knsimport",
> >> +                                      sizeof(*mod->ns_imports),
> >> +                                      &mod->num_ns_imports);
> >> +
> >>         mod->gpl_future_syms = section_objs(info,
> >>                                             "__ksymtab_gpl_future",
> >>                                             sizeof(*mod->gpl_future_syms),
> >> @@ -3381,6 +3443,19 @@ static int post_relocation(struct module *mod, const struct load_info *info)
> >>         return module_finalize(info->hdr, info->sechdrs, mod);
> >>  }
> >>
> >> +static void verify_namespace_dependencies(struct module *mod)
> >> +{
> >> +       struct module_ns_dep *ns_dep;
> >> +
> >> +       list_for_each_entry(ns_dep, &mod->ns_dependencies, ns_dep) {
> >> +               if (!module_imports_ns(mod, ns_dep->namespace)) {
> >> +                       pr_warn("%s: module uses symbols from namespace %s,"
> >> +                               " but does not import it.\n",
> >> +                               mod->name, ns_dep->namespace);
> >> +               }
> >> +       }
> >> +}
> >> +
> >>  /* Is this module of this name done loading?  No locks held. */
> >>  static bool finished_loading(const char *name)
> >>  {
> >> @@ -3682,6 +3757,8 @@ static int load_module(struct load_info *info, const char __user *uargs,
> >>         if (err)
> >>                 goto free_module;
> >>
> >> +       INIT_LIST_HEAD(&mod->ns_dependencies);
> >> +
> >>  #ifdef CONFIG_MODULE_SIG
> >>         mod->sig_ok = info->sig_ok;
> >>         if (!mod->sig_ok) {
> >> @@ -3730,6 +3807,8 @@ static int load_module(struct load_info *info, const char __user *uargs,
> >>         if (err < 0)
> >>                 goto free_modinfo;
> >>
> >> +       verify_namespace_dependencies(mod);
> >> +
> >>         flush_module_icache(mod);
> >>
> >>         /* Now copy in args */
> >> --
> >> 2.18.0.203.gfac676dfb9-goog
> >>



-- 
Lucas De Marchi