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module: Provide EXPORT_SYMBOL_GPL_FOR_MODULES() helper

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Helper macro to more easily limit the export of a symbol to a given
list of modules.

Eg:

  EXPORT_SYMBOL_GPL_FOR_MODULES(preempt_notifier_inc, "kvm");

will limit the use of said function to kvm.ko, any other module trying
to use this symbol will refure to load (and get modpost build
failures).

Requested-by: Masahiro Yamada <masahiroy@kernel.org>
Requested-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Reviewed-by: Petr Pavlu <petr.pavlu@suse.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
This commit is contained in:
Peter Zijlstra
2025-05-02 16:12:09 +02:00
committed by Masahiro Yamada
parent 0267cbf297
commit 707f853d7f
2 changed files with 32 additions and 2 deletions
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22
Documentation/core-api/symbol-namespaces.rst
View File

@@ -28,6 +28,9 @@ kernel. As of today, modules that make use of symbols exported into namespaces,
are required to import the namespace. Otherwise the kernel will, depending on
its configuration, reject loading the module or warn about a missing import.
Additionally, it is possible to put symbols into a module namespace, strictly
limiting which modules are allowed to use these symbols.
2. How to define Symbol Namespaces
==================================
@@ -83,6 +86,22 @@ unit as preprocessor statement. The above example would then read::
within the corresponding compilation unit before the #include for
<linux/export.h>. Typically it's placed before the first #include statement.
2.3 Using the EXPORT_SYMBOL_GPL_FOR_MODULES() macro
===================================================
Symbols exported using this macro are put into a module namespace. This
namespace cannot be imported.
The macro takes a comma separated list of module names, allowing only those
modules to access this symbol. Simple tail-globs are supported.
For example:
EXPORT_SYMBOL_GPL_FOR_MODULES(preempt_notifier_inc, "kvm,kvm-*")
will limit usage of this symbol to modules whoes name matches the given
patterns.
3. How to use Symbols exported in Namespaces
============================================
@@ -154,3 +173,6 @@ in-tree modules::
You can also run nsdeps for external module builds. A typical usage is::
$ make -C <path_to_kernel_src> M=$PWD nsdeps
Note: it will happily generate an import statement for the module namespace;
which will not work and generates build and runtime failures.

12
include/linux/export.h
View File

@@ -24,11 +24,17 @@
.long sym
#endif
#define ___EXPORT_SYMBOL(sym, license, ns) \
/*
* LLVM integrated assembler cam merge adjacent string literals (like
* C and GNU-as) passed to '.ascii', but not to '.asciz' and chokes on:
*
* .asciz "MODULE_" "kvm" ;
*/
#define ___EXPORT_SYMBOL(sym, license, ns...) \
.section ".export_symbol","a" ASM_NL \
__export_symbol_##sym: ASM_NL \
.asciz license ASM_NL \
.asciz ns ASM_NL \
.ascii ns "\0" ASM_NL \
__EXPORT_SYMBOL_REF(sym) ASM_NL \
.previous
@@ -85,4 +91,6 @@
#define EXPORT_SYMBOL_NS(sym, ns) __EXPORT_SYMBOL(sym, "", ns)
#define EXPORT_SYMBOL_NS_GPL(sym, ns) __EXPORT_SYMBOL(sym, "GPL", ns)
#define EXPORT_SYMBOL_GPL_FOR_MODULES(sym, mods) __EXPORT_SYMBOL(sym, "GPL", "module:" mods)
#endif /* _LINUX_EXPORT_H */