Messages in this thread Patch in this message |  | | Date | Thu, 25 Oct 2018 13:42:28 +0200 | From | Jessica Yu <> | Subject | Re: [PATCH] arm64/module: use mod->klp_info section header information |
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+++ Miroslav Benes [25/10/18 11:00 +0200]: >On Thu, 25 Oct 2018, Petr Mladek wrote: > >> On Tue 2018-10-23 19:55:54, Jessica Yu wrote: >> > The arm64 module loader keeps a pointer into info->sechdrs to keep track >> > of section header information for .plt section(s). A pointer to the >> > relevent section header (struct elf64_shdr) in info->sechdrs is stored >> > in mod->arch.{init,core}.plt. This pointer may be accessed while >> > applying relocations in apply_relocate_add() for example. And unlike >> > normal modules, livepatch modules can call apply_relocate_add() after >> > module load. But the info struct (and therefore info->sechdrs) gets >> > freed at the end of load_module() and so mod->arch.{init,core}.plt >> > becomes an invalid pointer after the module is done loading. >> > >> > Luckily, livepatch modules already keep a copy of Elf section header >> > information in mod->klp_info. So make sure livepatch modules on arm64 >> > have access to the section headers in klp_info and set >> > mod->arch.{init,core}.plt to the appropriate section header in >> > mod->klp_info so that they can call apply_relocate_add() even after >> > module load. >> > >> > diff --git a/kernel/module.c b/kernel/module.c >> > index f475f30eed8c..f3ac04cc9fc3 100644 >> > --- a/kernel/module.c >> > +++ b/kernel/module.c >> > @@ -3367,6 +3367,8 @@ int __weak module_finalize(const Elf_Ehdr *hdr, >> > >> > static int post_relocation(struct module *mod, const struct load_info *info) >> > { >> > + int err; >> > + >> > /* Sort exception table now relocations are done. */ >> > sort_extable(mod->extable, mod->extable + mod->num_exentries); >> > >> > @@ -3377,8 +3379,18 @@ static int post_relocation(struct module *mod, const struct load_info *info) >> > /* Setup kallsyms-specific fields. */ >> > add_kallsyms(mod, info); >> > >> > + if (is_livepatch_module(mod)) { >> > + err = copy_module_elf(mod, info); >> > + if (err < 0) >> > + return err; >> > + } >> > + >> > /* Arch-specific module finalizing. */ >> > - return module_finalize(info->hdr, info->sechdrs, mod); >> > + err = module_finalize(info->hdr, info->sechdrs, mod); >> > + if (err < 0) >> >> if (err < 0 && is_livepatch_module(mod)) > >Ah, right. > >> > + free_module_elf(mod); >> > + >> > + return err; >> > } >> >> Also we need to free the copied stuff in load_module() when >> anything called after post_relocation() fails. I think >> that the following would work: >> >> --- a/kernel/module.c >> +++ b/kernel/module.c >> @@ -3823,6 +3823,8 @@ static int load_module(struct load_info *info, const char __user *uargs, >> kfree(mod->args); >> free_arch_cleanup: >> module_arch_cleanup(mod); >> + if (is_livepatch_module(mod)) >> + free_module_elf(mod); >> free_modinfo: >> free_modinfo(mod); >> free_unload: > >Yes, we need to free it somewhere and I missed it. free_arch_cleanup seems >to be the correct place.
Good catches, thank you both!
>> But I suggest to just move copy_module_elf() up and keep >> calling it from load_module() directly. It would make >> the error handling more clear. > >Unfortunately it is not that simple. arm64's module_finalize() uses >mod->klp_info with the patch, so copy_module_elf() must be called before. >We could move module_finalize() from post_relocation() to load_module() >and place copy_module_elf() between those two, but I don't know. That's up >to Jessica.
Yeah, it's a stylistic preference - will shuffle those calls around and see what looks best. v2 to come shortly.
Thanks!
Jessica
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