Messages in this thread | | | Date | Tue, 27 Aug 2019 17:04:13 +0100 | From | Matthias Maennich <> | Subject | Re: [PATCH v3 03/11] module: add support for symbol namespaces. |
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On Tue, Aug 27, 2019 at 05:37:18PM +0200, Jessica Yu wrote: >+++ Matthias Maennich [21/08/19 12:49 +0100]: >>The EXPORT_SYMBOL_NS() and EXPORT_SYMBOL_NS_GPL() macros can be used to >>export a symbol to a specific namespace. There are no _GPL_FUTURE and >>_UNUSED variants because these are currently unused, and I'm not sure >>they are necessary. >> >>I didn't add EXPORT_SYMBOL_NS() for ASM exports; this patch sets the >>namespace of ASM exports to NULL by default. In case of relative >>references, it will be relocatable to NULL. If there's a need, this >>should be pretty easy to add. >> >>A module that wants to use a symbol exported to a namespace must add a >>MODULE_IMPORT_NS() statement to their module code; otherwise, modpost >>will complain when building the module, and the kernel module loader >>will emit an error and fail when loading the module. >> >>MODULE_IMPORT_NS() adds a modinfo tag 'import_ns' to the module. That >>tag can be observed by the modinfo command, modpost and kernel/module.c >>at the time of loading the module. >> >>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 >>relocation records just to get to the struct kernel_symbols. >> >>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. >> >>Co-developed-by: Martijn Coenen <maco@android.com> >>Signed-off-by: Martijn Coenen <maco@android.com> >>Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> >>Signed-off-by: Matthias Maennich <maennich@google.com> >>--- >>include/asm-generic/export.h | 6 +-- >>include/linux/export.h | 85 ++++++++++++++++++++++++++++++------ >>include/linux/module.h | 2 + >>kernel/module.c | 43 ++++++++++++++++++ >>4 files changed, 120 insertions(+), 16 deletions(-) >> >>diff --git a/include/asm-generic/export.h b/include/asm-generic/export.h >>index 63f54907317b..e2b5d0f569d3 100644 >>--- a/include/asm-generic/export.h >>+++ b/include/asm-generic/export.h >>@@ -17,11 +17,11 @@ >> >>.macro __put, val, name >>#ifdef CONFIG_HAVE_ARCH_PREL32_RELOCATIONS >>- .long \val - ., \name - . >>+ .long \val - ., \name - ., 0 - . >>#elif defined(CONFIG_64BIT) >>- .quad \val, \name >>+ .quad \val, \name, 0 >>#else >>- .long \val, \name >>+ .long \val, \name, 0 >>#endif >>.endm >> >>diff --git a/include/linux/export.h b/include/linux/export.h >>index 28a4d2150689..8e12e05444d1 100644 >>--- a/include/linux/export.h >>+++ b/include/linux/export.h >>@@ -20,6 +20,8 @@ extern struct module __this_module; >> >>#ifdef CONFIG_MODULES >> >>+#define NS_SEPARATOR "." >>+ >>#if defined(__KERNEL__) && !defined(__GENKSYMS__) >>#ifdef CONFIG_MODVERSIONS >>/* Mark the CRC weak since genksyms apparently decides not to >>@@ -49,6 +51,16 @@ extern struct module __this_module; >> * absolute relocations that require runtime processing on relocatable >> * kernels. >> */ >>+#define __KSYMTAB_ENTRY_NS(sym, sec, ns) \ >>+ __ADDRESSABLE(sym) \ >>+ asm(" .section \"___ksymtab" sec "+" #sym "\", \"a\" \n" \ >>+ " .balign 4 \n" \ >>+ "__ksymtab_" #sym NS_SEPARATOR #ns ": \n" \ >>+ " .long " #sym "- . \n" \ >>+ " .long __kstrtab_" #sym "- . \n" \ >>+ " .long __kstrtab_ns_" #sym "- . \n" \ >>+ " .previous \n") >>+ >>#define __KSYMTAB_ENTRY(sym, sec) \ >> __ADDRESSABLE(sym) \ >> asm(" .section \"___ksymtab" sec "+" #sym "\", \"a\" \n" \ >>@@ -56,32 +68,53 @@ extern struct module __this_module; >> "__ksymtab_" #sym ": \n" \ >> " .long " #sym "- . \n" \ >> " .long __kstrtab_" #sym "- . \n" \ >>+ " .long 0 - . \n" \ >> " .previous \n") >> >>struct kernel_symbol { >> int value_offset; >> int name_offset; >>+ int namespace_offset; >>}; >>#else >>+#define __KSYMTAB_ENTRY_NS(sym, sec, ns) \ >>+ static const struct kernel_symbol __ksymtab_##sym##__##ns \ >>+ asm("__ksymtab_" #sym NS_SEPARATOR #ns) \ >>+ __attribute__((section("___ksymtab" sec "+" #sym), used)) \ >>+ __aligned(sizeof(void *)) \ >>+ = { (unsigned long)&sym, __kstrtab_##sym, __kstrtab_ns_##sym} > >Style nit: missing space after __kstrtab_ns_##sym. > >>+ >>#define __KSYMTAB_ENTRY(sym, sec) \ >> static const struct kernel_symbol __ksymtab_##sym \ >>+ asm("__ksymtab_" #sym) \ >> __attribute__((section("___ksymtab" sec "+" #sym), used)) \ >> __aligned(sizeof(void *)) \ >>- = { (unsigned long)&sym, __kstrtab_##sym } >>+ = { (unsigned long)&sym, __kstrtab_##sym, NULL } >> >>struct kernel_symbol { >> unsigned long value; >> const char *name; >>+ const char *namespace; >>}; >>#endif >> >>-/* For every exported symbol, place a struct in the __ksymtab section */ >>-#define ___EXPORT_SYMBOL(sym, sec) \ >>+#define ___export_symbol_common(sym, sec) \ >> extern typeof(sym) sym; \ >> __CRC_SYMBOL(sym, sec) \ >> static const char __kstrtab_##sym[] \ >> __attribute__((section("__ksymtab_strings"), used, aligned(1))) \ >>- = #sym; \ >>+ = #sym \ > >Any particular reason for this change? Not that it's important, just >noticing the inconsistent inclusion of the semicolon in some of the >macros (e.g. __CRC_SYMBOL includes it but __export_symbol_common doesn't). >
I tried to be consistent to let the macro "call site" provide the final semicolon. And you are right, I could have adjusted __CRC_SYMBOL as well. I will adjust this for the next version.
>>+ >>+/* For every exported symbol, place a struct in the __ksymtab section */ >>+#define ___EXPORT_SYMBOL_NS(sym, sec, ns) \ >>+ ___export_symbol_common(sym, sec); \ >>+ static const char __kstrtab_ns_##sym[] \ >>+ __attribute__((section("__ksymtab_strings"), used, aligned(1))) \ >>+ = #ns; \ >>+ __KSYMTAB_ENTRY_NS(sym, sec, ns) >>+ >>+#define ___EXPORT_SYMBOL(sym, sec) \ >>+ ___export_symbol_common(sym, sec); \ >> __KSYMTAB_ENTRY(sym, sec) >> >>#if defined(__DISABLE_EXPORTS) >>@@ -91,6 +124,7 @@ struct kernel_symbol { >> * be reused in other execution contexts such as the UEFI stub or the >> * decompressor. >> */ >>+#define __EXPORT_SYMBOL_NS(sym, sec, ns) >>#define __EXPORT_SYMBOL(sym, sec) >> >>#elif defined(CONFIG_TRIM_UNUSED_KSYMS) >>@@ -117,18 +151,26 @@ struct kernel_symbol { >>#define __cond_export_sym_1(sym, sec) ___EXPORT_SYMBOL(sym, sec) >>#define __cond_export_sym_0(sym, sec) /* nothing */ >> >>+#define __EXPORT_SYMBOL_NS(sym, sec, ns) \ >>+ __ksym_marker(sym); \ >>+ __cond_export_ns_sym(sym, sec, ns, __is_defined(__KSYM_##sym)) >>+#define __cond_export_ns_sym(sym, sec, ns, conf) \ >>+ ___cond_export_ns_sym(sym, sec, ns, conf) >>+#define ___cond_export_ns_sym(sym, sec, ns, enabled) \ >>+ __cond_export_ns_sym_##enabled(sym, sec, ns) >>+#define __cond_export_ns_sym_1(sym, sec, ns) ___EXPORT_SYMBOL_NS(sym, sec, ns) >>+#define __cond_export_ns_sym_0(sym, sec, ns) /* nothing */ >>+ >>#else >>+#define __EXPORT_SYMBOL_NS ___EXPORT_SYMBOL_NS >>#define __EXPORT_SYMBOL ___EXPORT_SYMBOL >>#endif >> >>-#define EXPORT_SYMBOL(sym) \ >>- __EXPORT_SYMBOL(sym, "") >>- >>-#define EXPORT_SYMBOL_GPL(sym) \ >>- __EXPORT_SYMBOL(sym, "_gpl") >>- >>-#define EXPORT_SYMBOL_GPL_FUTURE(sym) \ >>- __EXPORT_SYMBOL(sym, "_gpl_future") >>+#define EXPORT_SYMBOL(sym) __EXPORT_SYMBOL(sym, "") >>+#define EXPORT_SYMBOL_GPL(sym) __EXPORT_SYMBOL(sym, "_gpl") >>+#define EXPORT_SYMBOL_GPL_FUTURE(sym) __EXPORT_SYMBOL(sym, "_gpl_future") >>+#define EXPORT_SYMBOL_NS(sym, ns) __EXPORT_SYMBOL_NS(sym, "", ns) >>+#define EXPORT_SYMBOL_NS_GPL(sym, ns) __EXPORT_SYMBOL_NS(sym, "_gpl", ns) >> >>#ifdef CONFIG_UNUSED_SYMBOLS >>#define EXPORT_UNUSED_SYMBOL(sym) __EXPORT_SYMBOL(sym, "_unused") >>@@ -138,11 +180,28 @@ struct kernel_symbol { >>#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) >>diff --git a/include/linux/module.h b/include/linux/module.h >>index 1455812dd325..b3611e749f72 100644 >>--- a/include/linux/module.h >>+++ b/include/linux/module.h >>@@ -280,6 +280,8 @@ struct notifier_block; >> >>#ifdef CONFIG_MODULES >> >>+#define MODULE_IMPORT_NS(ns) MODULE_INFO(import_ns, #ns) >>+ >>extern int modules_disabled; /* for sysctl */ >>/* Get/put a kernel symbol (calls must be symmetric) */ >>void *__symbol_get(const char *symbol); >>diff --git a/kernel/module.c b/kernel/module.c >>index a23067907169..57e8253f2251 100644 >>--- a/kernel/module.c >>+++ b/kernel/module.c >>@@ -544,6 +544,15 @@ static const char *kernel_symbol_name(const struct kernel_symbol *sym) >>#endif >>} >> >>+static const char *kernel_symbol_namespace(const struct kernel_symbol *sym) >>+{ >>+#ifdef CONFIG_HAVE_ARCH_PREL32_RELOCATIONS >>+ return offset_to_ptr(&sym->namespace_offset); >>+#else >>+ return sym->namespace; >>+#endif >>+} >>+ >>static int cmp_name(const void *va, const void *vb) >>{ >> const char *a; >>@@ -1379,6 +1388,34 @@ static inline int same_magic(const char *amagic, const char *bmagic, >>} >>#endif /* CONFIG_MODVERSIONS */ >> >>+static char *get_modinfo(const struct load_info *info, const char *tag); >>+static char *get_next_modinfo(const struct load_info *info, const char *tag, >>+ char *prev); >>+ >>+static int verify_namespace_is_imported(const struct load_info *info, >>+ const struct kernel_symbol *sym, >>+ struct module *mod) >>+{ >>+ const char *namespace; >>+ char *imported_namespace; >>+ >>+ namespace = kernel_symbol_namespace(sym); >>+ if (namespace) { >>+ imported_namespace = get_modinfo(info, "import_ns"); >>+ while (imported_namespace) { >>+ if (strcmp(namespace, imported_namespace) == 0) >>+ return 0; >>+ imported_namespace = get_next_modinfo( >>+ info, "import_ns", imported_namespace); >>+ } >>+ pr_err("%s: module uses symbol (%s) from namespace %s, but does not import it.\n", >>+ mod->name, kernel_symbol_name(sym), namespace); >>+ return -EINVAL; >>+ } >>+ return 0; >>+} >>+ >>+ >>/* Resolve a symbol for this module. I.e. if we find one, record usage. */ >>static const struct kernel_symbol *resolve_symbol(struct module *mod, >> const struct load_info *info, >>@@ -1413,6 +1450,12 @@ static const struct kernel_symbol *resolve_symbol(struct module *mod, >> goto getname; >> } >> >>+ err = verify_namespace_is_imported(info, sym, mod); >>+ if (err) { >>+ sym = ERR_PTR(err); >>+ goto getname; >>+ } > >I think we should verify the namespace before taking a reference to >the owner module (just swap the verify_namespace_is_imported() and >ref_module() calls here). > >Other than that, this patch looks good. Thanks! >
Thanks! I will address the points above.
Cheers, Matthias
>>+ >>getname: >> /* We must make copy under the lock if we failed to get ref. */ >> strncpy(ownername, module_name(owner), MODULE_NAME_LEN); >>-- >>2.23.0.rc1.153.gdeed80330f-goog >>
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