module: add support for symbol namespaces.

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>
Signed-off-by: Jessica Yu <jeyu@kernel.org>

2 files changed, 77 insertions, 16 deletions

diff --git a/include/linux/export.h b/include/linux/export.h
index 28a4d2150689..d59461e71478 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
@@ -29,13 +31,13 @@ extern struct module __this_module;
         asm("   .section \"___kcrctab" sec "+" #sym "\", \"a\"  \n"     \
             "   .weak   __crc_" #sym "                          \n"     \
             "   .long   __crc_" #sym " - .                      \n"     \
-            "   .previous                                       \n");
+            "   .previous                                       \n")
 #else
 #define __CRC_SYMBOL(sym, sec)                                          \
         asm("   .section \"___kcrctab" sec "+" #sym "\", \"a\"  \n"     \
             "   .weak   __crc_" #sym "                          \n"     \
             "   .long   __crc_" #sym "                          \n"     \
-            "   .previous                                       \n");
+            "   .previous                                       \n")
 #endif
 #else
 #define __CRC_SYMBOL(sym, sec)
@@ -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 }
+
 #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)                                          \
+        __CRC_SYMBOL(sym, sec);                                         \
         static const char __kstrtab_##sym[]                             \
         __attribute__((section("__ksymtab_strings"), used, aligned(1))) \
-        = #sym;                                                         \
+        = #sym                                                          \
+
+/* 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);