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livepatch,x86: Clear relocation targets on a module removal

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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 eda9cec4c9
("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 <jpoimboe@redhat.com>
Originally-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Song Liu <song@kernel.org>
Acked-by: Miroslav Benes <mbenes@suse.cz>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
Reviewed-by: Joe Lawrence <joe.lawrence@redhat.com>
Tested-by: Joe Lawrence <joe.lawrence@redhat.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20230125185401.279042-2-song@kernel.org
This commit is contained in:
Song Liu
2023-01-25 10:54:01 -08:00
committed by Petr Mladek
parent bbb93362a4
commit 0c05e7bd2d
3 changed files with 126 additions and 46 deletions
Download Patch File Download Diff File Expand all files Collapse all files

62
kernel/livepatch/core.c
View File

@@ -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);
return apply_relocate_add(sechdrs, strtab, symndx, secndx, pmod);
}
clear_relocate_add(sechdrs, strtab, symndx, secndx, pmod);
return 0;
}
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;
}