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 <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
diff --git a/arch/x86/kernel/module.c b/arch/x86/kernel/module.c
index 0a09d81..790fa9f 100644
--- a/arch/x86/kernel/module.c
+++ b/arch/x86/kernel/module.c
@@ -128,22 +128,27 @@
return 0;
}
#else /*X86_64*/
-static int __apply_relocate_add(Elf64_Shdr *sechdrs,
+static int __write_relocate_add(Elf64_Shdr *sechdrs,
const char *strtab,
unsigned int symindex,
unsigned int relsec,
struct module *me,
- void *(*write)(void *dest, const void *src, size_t len))
+ void *(*write)(void *dest, const void *src, size_t len),
+ bool apply)
{
unsigned int i;
Elf64_Rela *rel = (void *)sechdrs[relsec].sh_addr;
Elf64_Sym *sym;
void *loc;
u64 val;
+ u64 zero = 0ULL;
- DEBUGP("Applying relocate section %u to %u\n",
+ DEBUGP("%s relocate section %u to %u\n",
+ apply ? "Applying" : "Clearing",
relsec, sechdrs[relsec].sh_info);
for (i = 0; i < sechdrs[relsec].sh_size / sizeof(*rel); i++) {
+ size_t size;
+
/* This is where to make the change */
loc = (void *)sechdrs[sechdrs[relsec].sh_info].sh_addr
+ rel[i].r_offset;
@@ -161,52 +166,53 @@
switch (ELF64_R_TYPE(rel[i].r_info)) {
case R_X86_64_NONE:
- break;
+ continue; /* nothing to write */
case R_X86_64_64:
- if (*(u64 *)loc != 0)
- goto invalid_relocation;
- write(loc, &val, 8);
+ size = 8;
break;
case R_X86_64_32:
- if (*(u32 *)loc != 0)
- goto invalid_relocation;
- write(loc, &val, 4);
- if (val != *(u32 *)loc)
+ if (val != *(u32 *)&val)
goto overflow;
+ size = 4;
break;
case R_X86_64_32S:
- if (*(s32 *)loc != 0)
- goto invalid_relocation;
- write(loc, &val, 4);
- if ((s64)val != *(s32 *)loc)
+ if ((s64)val != *(s32 *)&val)
goto overflow;
+ size = 4;
break;
case R_X86_64_PC32:
case R_X86_64_PLT32:
- if (*(u32 *)loc != 0)
- goto invalid_relocation;
val -= (u64)loc;
- write(loc, &val, 4);
+ size = 4;
break;
case R_X86_64_PC64:
- if (*(u64 *)loc != 0)
- goto invalid_relocation;
val -= (u64)loc;
- write(loc, &val, 8);
+ size = 8;
break;
default:
pr_err("%s: Unknown rela relocation: %llu\n",
me->name, ELF64_R_TYPE(rel[i].r_info));
return -ENOEXEC;
}
+
+ if (apply) {
+ if (memcmp(loc, &zero, size)) {
+ pr_err("x86/modules: Invalid relocation target, existing value is nonzero for type %d, loc %p, val %Lx\n",
+ (int)ELF64_R_TYPE(rel[i].r_info), loc, val);
+ return -ENOEXEC;
+ }
+ write(loc, &val, size);
+ } else {
+ if (memcmp(loc, &val, size)) {
+ pr_warn("x86/modules: Invalid relocation target, existing value does not match expected value for type %d, loc %p, val %Lx\n",
+ (int)ELF64_R_TYPE(rel[i].r_info), loc, val);
+ return -ENOEXEC;
+ }
+ write(loc, &zero, size);
+ }
}
return 0;
-invalid_relocation:
- pr_err("x86/modules: Skipping invalid relocation target, existing value is nonzero for type %d, loc %p, val %Lx\n",
- (int)ELF64_R_TYPE(rel[i].r_info), loc, val);
- return -ENOEXEC;
-
overflow:
pr_err("overflow in relocation type %d val %Lx\n",
(int)ELF64_R_TYPE(rel[i].r_info), val);
@@ -215,11 +221,12 @@
return -ENOEXEC;
}
-int apply_relocate_add(Elf64_Shdr *sechdrs,
- const char *strtab,
- unsigned int symindex,
- unsigned int relsec,
- struct module *me)
+static int write_relocate_add(Elf64_Shdr *sechdrs,
+ const char *strtab,
+ unsigned int symindex,
+ unsigned int relsec,
+ struct module *me,
+ bool apply)
{
int ret;
bool early = me->state == MODULE_STATE_UNFORMED;
@@ -230,8 +237,8 @@
mutex_lock(&text_mutex);
}
- ret = __apply_relocate_add(sechdrs, strtab, symindex, relsec, me,
- write);
+ ret = __write_relocate_add(sechdrs, strtab, symindex, relsec, me,
+ write, apply);
if (!early) {
text_poke_sync();
@@ -241,6 +248,26 @@
return ret;
}
+int apply_relocate_add(Elf64_Shdr *sechdrs,
+ const char *strtab,
+ unsigned int symindex,
+ unsigned int relsec,
+ struct module *me)
+{
+ return write_relocate_add(sechdrs, strtab, symindex, relsec, me, true);
+}
+
+#ifdef CONFIG_LIVEPATCH
+void clear_relocate_add(Elf64_Shdr *sechdrs,
+ const char *strtab,
+ unsigned int symindex,
+ unsigned int relsec,
+ struct module *me)
+{
+ write_relocate_add(sechdrs, strtab, symindex, relsec, me, false);
+}
+#endif
+
#endif
int module_finalize(const Elf_Ehdr *hdr,
diff --git a/include/linux/moduleloader.h b/include/linux/moduleloader.h
index 9e09d11..2ba4bc8 100644
--- a/include/linux/moduleloader.h
+++ b/include/linux/moduleloader.h
@@ -72,6 +72,23 @@
unsigned int symindex,
unsigned int relsec,
struct module *mod);
+#ifdef CONFIG_LIVEPATCH
+/*
+ * Some architectures (namely x86_64 and ppc64) perform sanity checks when
+ * applying relocations. If a patched module gets unloaded and then later
+ * reloaded (and re-patched), klp re-applies relocations to the replacement
+ * function(s). Any leftover relocations from the previous loading of the
+ * patched module might trigger the sanity checks.
+ *
+ * To prevent that, when unloading a patched module, clear out any relocations
+ * that might trigger arch-specific sanity checks on a future module reload.
+ */
+void clear_relocate_add(Elf_Shdr *sechdrs,
+ const char *strtab,
+ unsigned int symindex,
+ unsigned int relsec,
+ struct module *me);
+#endif
#else
static inline int apply_relocate_add(Elf_Shdr *sechdrs,
const char *strtab,
diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index 9ada0bc..0168c38 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -261,6 +261,14 @@
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 @@
* 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 @@
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 @@
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 @@
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 @@
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 @@
klp_unpatch_object(obj);
klp_post_unpatch_callback(obj);
-
+ klp_clear_object_relocs(patch, obj);
klp_free_object_loaded(obj);
break;
}
