From 0c05e7bd2d017a3a9a0f4e9a19ad4acf1f616f12 Mon Sep 17 00:00:00 2001 From: Song Liu Date: Wed, 25 Jan 2023 10:54:01 -0800 Subject: livepatch,x86: Clear relocation targets on a module removal Josh reported a bug: When the object to be patched is a module, and that module is rmmod'ed and reloaded, it fails to load with: module: x86/modules: Skipping invalid relocation target, existing value is nonzero for type 2, loc 00000000ba0302e9, val ffffffffa03e293c livepatch: failed to initialize patch 'livepatch_nfsd' for module 'nfsd' (-8) livepatch: patch 'livepatch_nfsd' failed for module 'nfsd', refusing to load module 'nfsd' The livepatch module has a relocation which references a symbol in the _previous_ loading of nfsd. When apply_relocate_add() tries to replace the old relocation with a new one, it sees that the previous one is nonzero and it errors out. He also proposed three different solutions. We could remove the error check in apply_relocate_add() introduced by commit eda9cec4c9a1 ("x86/module: Detect and skip invalid relocations"). However the check is useful for detecting corrupted modules. We could also deny the patched modules to be removed. If it proved to be a major drawback for users, we could still implement a different approach. The solution would also complicate the existing code a lot. We thus decided to reverse the relocation patching (clear all relocation targets on x86_64). The solution is not universal and is too much arch-specific, but it may prove to be simpler in the end. Reported-by: Josh Poimboeuf Originally-by: Miroslav Benes Signed-off-by: Song Liu Acked-by: Miroslav Benes Reviewed-by: Petr Mladek Acked-by: Josh Poimboeuf Reviewed-by: Joe Lawrence Tested-by: Joe Lawrence Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20230125185401.279042-2-song@kernel.org --- kernel/livepatch/core.c | 62 ++++++++++++++++++++++++++++++++++++++----------- 1 file changed, 49 insertions(+), 13 deletions(-) (limited to 'kernel') diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c index 9ada0bc5247b..0168c38ba187 100644 --- a/kernel/livepatch/core.c +++ b/kernel/livepatch/core.c @@ -261,6 +261,14 @@ static int klp_resolve_symbols(Elf_Shdr *sechdrs, const char *strtab, return 0; } +void __weak clear_relocate_add(Elf_Shdr *sechdrs, + const char *strtab, + unsigned int symindex, + unsigned int relsec, + struct module *me) +{ +} + /* * At a high-level, there are two types of klp relocation sections: those which * reference symbols which live in vmlinux; and those which reference symbols @@ -284,10 +292,10 @@ static int klp_resolve_symbols(Elf_Shdr *sechdrs, const char *strtab, * the to-be-patched module to be loaded and patched sometime *after* the * klp module is loaded. */ -int klp_apply_section_relocs(struct module *pmod, Elf_Shdr *sechdrs, - const char *shstrtab, const char *strtab, - unsigned int symndx, unsigned int secndx, - const char *objname) +static int klp_write_section_relocs(struct module *pmod, Elf_Shdr *sechdrs, + const char *shstrtab, const char *strtab, + unsigned int symndx, unsigned int secndx, + const char *objname, bool apply) { int cnt, ret; char sec_objname[MODULE_NAME_LEN]; @@ -309,11 +317,26 @@ int klp_apply_section_relocs(struct module *pmod, Elf_Shdr *sechdrs, if (strcmp(objname ? objname : "vmlinux", sec_objname)) return 0; - ret = klp_resolve_symbols(sechdrs, strtab, symndx, sec, sec_objname); - if (ret) - return ret; + if (apply) { + ret = klp_resolve_symbols(sechdrs, strtab, symndx, + sec, sec_objname); + if (ret) + return ret; + + return apply_relocate_add(sechdrs, strtab, symndx, secndx, pmod); + } + + clear_relocate_add(sechdrs, strtab, symndx, secndx, pmod); + return 0; +} - return apply_relocate_add(sechdrs, strtab, symndx, secndx, pmod); +int klp_apply_section_relocs(struct module *pmod, Elf_Shdr *sechdrs, + const char *shstrtab, const char *strtab, + unsigned int symndx, unsigned int secndx, + const char *objname) +{ + return klp_write_section_relocs(pmod, sechdrs, shstrtab, strtab, symndx, + secndx, objname, true); } /* @@ -762,8 +785,9 @@ static int klp_init_func(struct klp_object *obj, struct klp_func *func) func->old_sympos ? func->old_sympos : 1); } -static int klp_apply_object_relocs(struct klp_patch *patch, - struct klp_object *obj) +static int klp_write_object_relocs(struct klp_patch *patch, + struct klp_object *obj, + bool apply) { int i, ret; struct klp_modinfo *info = patch->mod->klp_info; @@ -774,10 +798,10 @@ static int klp_apply_object_relocs(struct klp_patch *patch, if (!(sec->sh_flags & SHF_RELA_LIVEPATCH)) continue; - ret = klp_apply_section_relocs(patch->mod, info->sechdrs, + ret = klp_write_section_relocs(patch->mod, info->sechdrs, info->secstrings, patch->mod->core_kallsyms.strtab, - info->symndx, i, obj->name); + info->symndx, i, obj->name, apply); if (ret) return ret; } @@ -785,6 +809,18 @@ static int klp_apply_object_relocs(struct klp_patch *patch, return 0; } +static int klp_apply_object_relocs(struct klp_patch *patch, + struct klp_object *obj) +{ + return klp_write_object_relocs(patch, obj, true); +} + +static void klp_clear_object_relocs(struct klp_patch *patch, + struct klp_object *obj) +{ + klp_write_object_relocs(patch, obj, false); +} + /* parts of the initialization that is done only when the object is loaded */ static int klp_init_object_loaded(struct klp_patch *patch, struct klp_object *obj) @@ -1172,7 +1208,7 @@ static void klp_cleanup_module_patches_limited(struct module *mod, klp_unpatch_object(obj); klp_post_unpatch_callback(obj); - + klp_clear_object_relocs(patch, obj); klp_free_object_loaded(obj); break; } -- cgit v1.2.3