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@xxxxxxxxxxx>
Signed-off-by: Martijn Coenen <maco@xxxxxxxxxxx>
Reviewed-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Matthias Maennich <maennich@xxxxxxxxxx>
---
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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