4.4-stable review patch. If anyone has any objections, please let me know.
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From: Jessica Yu jeyu@kernel.org
[ 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 --- kernel/module.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)
--- a/kernel/module.c +++ b/kernel/module.c @@ -3860,7 +3860,7 @@ static unsigned long mod_find_symname(st
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; } @@ -3906,6 +3906,10 @@ int module_kallsyms_on_each_symbol(int ( 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)