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Subject[RFC] EXPORT_SYMBOL_GPL_FUTURE()
Currently we don't have a way to show people that some kernel symbols
will be changed in the future from EXPORT_SYMBOL() to
EXPORT_SYMBOL_GPL(). As we all know, not everyone reads the
Documentation/feature_removal.txt file, so we need a bigger way to
remind people.

So, here's a patch that implements EXPORT_SYMBOL_GPL_FUTURE(). It
basically says that some time in the future, this symbol is going to
change and not be allowed to be called from non-GPL licensed kernel
modules.

Now I'm not wed to the name, so if anyone else has a better suggestion
as to what to call this, please let me know. I also feel that the text
that is spit out to the kernel log is a bit stilted, so again,
suggestions welcome.

Comments?

I only implemented this for those arches and sub-arches that use the
asm-generic/vmlinux.lds.h file. I think there are still a few others
out there that do not do this, so I'll have to fix them up too for the
final version of this patch.

thanks,

greg k-h


---------------------
From: Greg Kroah-Hartman <gregkh@suse.de>
Subject: [PATCH] add EXPORT_SYMBOL_GPL_FUTURE()
This patch adds the ability to mark symbols that will be changed in the
future, so that non-GPL usage of them is flagged by the kernel and
printed out to the system log.


Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>


---
include/asm-generic/vmlinux.lds.h | 14 ++++++++++++
include/linux/module.h | 8 +++++++
kernel/module.c | 36 +++++++++++++++++++++++++++++++--
--- gregkh-2.6.orig/include/asm-generic/vmlinux.lds.h
+++ gregkh-2.6/include/asm-generic/vmlinux.lds.h
@@ -58,6 +58,13 @@
VMLINUX_SYMBOL(__stop___ksymtab_gpl) = .; \
} \
\
+ /* Kernel symbol table: GPL-future-only symbols */ \
+ __ksymtab_gpl_future : AT(ADDR(__ksymtab_gpl_future) - LOAD_OFFSET) { \
+ VMLINUX_SYMBOL(__start___ksymtab_gpl_future) = .; \
+ *(__ksymtab_gpl_future) \
+ VMLINUX_SYMBOL(__stop___ksymtab_gpl_future) = .; \
+ } \
+ \
/* Kernel symbol table: Normal symbols */ \
__kcrctab : AT(ADDR(__kcrctab) - LOAD_OFFSET) { \
VMLINUX_SYMBOL(__start___kcrctab) = .; \
@@ -72,6 +79,13 @@
VMLINUX_SYMBOL(__stop___kcrctab_gpl) = .; \
} \
\
+ /* Kernel symbol table: GPL-only symbols */ \
+ __kcrctab_gpl_future : AT(ADDR(__kcrctab_gpl_future) - LOAD_OFFSET) { \
+ VMLINUX_SYMBOL(__start___kcrctab_gpl_future) = .; \
+ *(__kcrctab_gpl_future) \
+ VMLINUX_SYMBOL(__stop___kcrctab_gpl_future) = .; \
+ } \
+ \
/* Kernel symbol table: strings */ \
__ksymtab_strings : AT(ADDR(__ksymtab_strings) - LOAD_OFFSET) { \
*(__ksymtab_strings) \
--- gregkh-2.6.orig/include/linux/module.h
+++ gregkh-2.6/include/linux/module.h
@@ -198,6 +198,9 @@ void *__symbol_get_gpl(const char *symbo
#define EXPORT_SYMBOL_GPL(sym) \
__EXPORT_SYMBOL(sym, "_gpl")

+#define EXPORT_SYMBOL_GPL_FUTURE(sym) \
+ __EXPORT_SYMBOL(sym, "_gpl_future")
+
#endif

struct module_ref
@@ -255,6 +258,11 @@ struct module
unsigned int num_gpl_syms;
const unsigned long *gpl_crcs;

+ /* symbols that will be GPL-only in the near future. */
+ const struct kernel_symbol *gpl_future_syms;
+ unsigned int num_gpl_future_syms;
+ const unsigned long *gpl_future_crcs;
+
/* Exception table */
unsigned int num_exentries;
const struct exception_table_entry *extable;
--- gregkh-2.6.orig/kernel/module.c
+++ gregkh-2.6/kernel/module.c
@@ -126,8 +126,11 @@ extern const struct kernel_symbol __star
extern const struct kernel_symbol __stop___ksymtab[];
extern const struct kernel_symbol __start___ksymtab_gpl[];
extern const struct kernel_symbol __stop___ksymtab_gpl[];
+extern const struct kernel_symbol __start___ksymtab_gpl_future[];
+extern const struct kernel_symbol __stop___ksymtab_gpl_future[];
extern const unsigned long __start___kcrctab[];
extern const unsigned long __start___kcrctab_gpl[];
+extern const unsigned long __start___kcrctab_gpl_future[];

#ifndef CONFIG_MODVERSIONS
#define symversion(base, idx) NULL
@@ -159,6 +162,16 @@ static unsigned long __find_symbol(const
return __start___ksymtab_gpl[i].value;
}
}
+ for (i = 0; __start___ksymtab_gpl_future+i < __stop___ksymtab_gpl_future; i++) {
+ if (strcmp(__start___ksymtab_gpl_future[i].name, name) == 0) {
+ *crc = symversion(__start___kcrctab_gpl_future, i);
+ if (!gplok)
+ printk(KERN_WARNING "symbol %s is being used "
+ "by a non-GPL module, which will not "
+ "be allowed in the future\n", name);
+ return __start___ksymtab_gpl_future[i].value;
+ }
+ }

/* Now try modules. */
list_for_each_entry(mod, &modules, list) {
@@ -177,6 +190,16 @@ static unsigned long __find_symbol(const
}
}
}
+ for (i = 0; i < mod->num_gpl_future_syms; i++) {
+ if (strcmp(mod->gpl_future_syms[i].name, name) == 0) {
+ *crc = symversion(mod->gpl_future_crcs, i);
+ if (!gplok)
+ printk(KERN_WARNING "symbol %s is being used "
+ "by a non-GPL module, which will not "
+ "be allowed in the future\n", name);
+ return mod->gpl_future_syms[i].value;
+ }
+ }
}
DEBUGP("Failed to find symbol %s\n", name);
return 0;
@@ -1537,7 +1560,8 @@ static struct module *load_module(void _
char *secstrings, *args, *modmagic, *strtab = NULL;
unsigned int i, symindex = 0, strindex = 0, setupindex, exindex,
exportindex, modindex, obsparmindex, infoindex, gplindex,
- crcindex, gplcrcindex, versindex, pcpuindex;
+ crcindex, gplcrcindex, versindex, pcpuindex, gplfutureindex,
+ gplfuturecrcindex;
long arglen;
struct module *mod;
long err = 0;
@@ -1618,8 +1642,10 @@ static struct module *load_module(void _
/* Optional sections */
exportindex = find_sec(hdr, sechdrs, secstrings, "__ksymtab");
gplindex = find_sec(hdr, sechdrs, secstrings, "__ksymtab_gpl");
+ gplfutureindex = find_sec(hdr, sechdrs, secstrings, "__ksymtab_gpl_future");
crcindex = find_sec(hdr, sechdrs, secstrings, "__kcrctab");
gplcrcindex = find_sec(hdr, sechdrs, secstrings, "__kcrctab_gpl");
+ gplfuturecrcindex = find_sec(hdr, sechdrs, secstrings, "__kcrctab_gpl_future");
setupindex = find_sec(hdr, sechdrs, secstrings, "__param");
exindex = find_sec(hdr, sechdrs, secstrings, "__ex_table");
obsparmindex = find_sec(hdr, sechdrs, secstrings, "__obsparm");
@@ -1772,10 +1798,16 @@ static struct module *load_module(void _
mod->gpl_syms = (void *)sechdrs[gplindex].sh_addr;
if (gplcrcindex)
mod->gpl_crcs = (void *)sechdrs[gplcrcindex].sh_addr;
+ mod->num_gpl_future_syms = sechdrs[gplfutureindex].sh_size /
+ sizeof(*mod->gpl_future_syms);
+ mod->gpl_future_syms = (void *)sechdrs[gplfutureindex].sh_addr;
+ if (gplfuturecrcindex)
+ mod->gpl_future_crcs = (void *)sechdrs[gplfuturecrcindex].sh_addr;

#ifdef CONFIG_MODVERSIONS
if ((mod->num_syms && !crcindex) ||
- (mod->num_gpl_syms && !gplcrcindex)) {
+ (mod->num_gpl_syms && !gplcrcindex) ||
+ (mod->num_gpl_future_syms && !gplfuturecrcindex)) {
printk(KERN_WARNING "%s: No versions for exported symbols."
" Tainting kernel.\n", mod->name);
add_taint(TAINT_FORCED_MODULE);
-
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