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module: add support for symbol namespaces.
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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>
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Matthias Maennich authored and Jessica Yu committed Sep 10, 2019
1 parent ed13fc3 commit 8651ec0
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Showing 4 changed files with 123 additions and 19 deletions.
6 changes: 3 additions & 3 deletions include/asm-generic/export.h
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Original file line number Diff line number Diff line change
Expand Up @@ -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

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91 changes: 75 additions & 16 deletions include/linux/export.h
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Original file line number Diff line number Diff line change
Expand Up @@ -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
Expand All @@ -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)
Expand All @@ -49,39 +51,70 @@ 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" \
" .balign 4 \n" \
"__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)
Expand All @@ -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)
Expand All @@ -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")
Expand All @@ -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)
Expand Down
2 changes: 2 additions & 0 deletions include/linux/module.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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);
Expand Down
43 changes: 43 additions & 0 deletions kernel/module.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand Down Expand Up @@ -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,
Expand Down Expand Up @@ -1407,6 +1444,12 @@ 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;
}

err = ref_module(mod, owner);
if (err) {
sym = ERR_PTR(err);
Expand Down

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