module: exclude SHN_UNDEF symbols from kallsyms api

[ Upstream commit 9f2d1e68cf4d641def734adaccfc3823d3575e6c ]

Livepatch modules are special in that we preserve their entire symbol
tables in order to be able to apply relocations after module load. The
unwanted side effect of this is that undefined (SHN_UNDEF) symbols of
livepatch modules are accessible via the kallsyms api and this can
confuse symbol resolution in livepatch (klp_find_object_symbol()) and
cause subtle bugs in livepatch.

Have the module kallsyms api skip over SHN_UNDEF symbols. These symbols
are usually not available for normal modules anyway as we cut down their
symbol tables to just the core (non-undefined) symbols, so this should
really just affect livepatch modules. Note that this patch doesn't
affect the display of undefined symbols in /proc/kallsyms.

Reported-by: Josh Poimboeuf <jpoimboe@redhat.com>
Tested-by: Josh Poimboeuf <jpoimboe@redhat.com>
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Jessica Yu <jeyu@kernel.org>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/kernel/module.c b/kernel/module.c
index 0651f2d25fc9d790785758c17b93327f4e894ad6..2325c9821f2a105220b15b8cb926a236d56304d5 100644 (file)
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -4011,7 +4011,7 @@ static unsigned long mod_find_symname(struct module *mod, const char *name)
 
        for (i = 0; i < kallsyms->num_symtab; i++)
                if (strcmp(name, symname(kallsyms, i)) == 0 &&
-                   kallsyms->symtab[i].st_info != 'U')
+                   kallsyms->symtab[i].st_shndx != SHN_UNDEF)
                        return kallsyms->symtab[i].st_value;
        return 0;
 }
@@ -4057,6 +4057,10 @@ int module_kallsyms_on_each_symbol(int (*fn)(void *, const char *,
                if (mod->state == MODULE_STATE_UNFORMED)
                        continue;
                for (i = 0; i < kallsyms->num_symtab; i++) {
+
+                       if (kallsyms->symtab[i].st_shndx == SHN_UNDEF)
+                               continue;
+
                        ret = fn(data, symname(kallsyms, i),
                                 mod, kallsyms->symtab[i].st_value);
                        if (ret != 0)