From: Miroslav Benes <mbenes@xxxxxxx>
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.
On ppc64le, we have a similar issue:
module_64: livepatch_nfsd: Expected nop after call, got e8410018 at e_show+0x60/0x548 [livepatch_nfsd]
livepatch: failed to initialize patch 'livepatch_nfsd' for module 'nfsd' (-8)
livepatch: patch 'livepatch_nfsd' failed for module 'nfsd', refusing to load module 'nfsd'
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@xxxxxxxxxx>
Signed-off-by: Miroslav Benes <mbenes@xxxxxxx>
Signed-off-by: Song Liu <song@xxxxxxxxxx>
---
NOTE: powerpc code has not be tested.
Changes v3 = v4:
1. Reuse __apply_relocate_add to make it more reliable in long term.
(Josh Poimboeuf)
2. Add back ppc64 logic from v2, with changes to match current code.
(Josh Poimboeuf)
Changes v2 => v3:
1. Rewrite x86 changes to match current code style.
2. Remove powerpc changes as there is no test coverage in v3.
3. Only keep 1/3 of v2.
v2: https://lore.kernel.org/all/20190905124514.8944-1-mbenes@xxxxxxx/T/#u
---
arch/powerpc/kernel/module_64.c | 49 +++++++++++++++
arch/s390/kernel/module.c | 8 +++
arch/x86/kernel/module.c | 102 +++++++++++++++++++++++---------
include/linux/moduleloader.h | 7 +++
kernel/livepatch/core.c | 41 ++++++++++++-
5 files changed, 179 insertions(+), 28 deletions(-)
diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c
index 7e45dc98df8a..1834dffc6795 100644
--- a/arch/powerpc/kernel/module_64.c
+++ b/arch/powerpc/kernel/module_64.c
@@ -739,6 +739,55 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
return 0;
}
+#ifdef CONFIG_LIVEPATCH
+void clear_relocate_add(Elf64_Shdr *sechdrs,
+ const char *strtab,
+ unsigned int symindex,
+ unsigned int relsec,
+ struct module *me)
+{
+ unsigned int i;
+ Elf64_Rela *rela = (void *)sechdrs[relsec].sh_addr;
+ Elf64_Sym *sym;
+ unsigned long *location;
+ const char *symname;
+ u32 *instruction;
+
+ pr_debug("Clearing ADD relocate section %u to %u\n", relsec,
+ sechdrs[relsec].sh_info);
+
+ for (i = 0; i < sechdrs[relsec].sh_size / sizeof(*rela); i++) {
+ location = (void *)sechdrs[sechdrs[relsec].sh_info].sh_addr
+ + rela[i].r_offset;
+ sym = (Elf64_Sym *)sechdrs[symindex].sh_addr
+ + ELF64_R_SYM(rela[i].r_info);
+ symname = me->core_kallsyms.strtab
+ + sym->st_name;
+
+ if (ELF64_R_TYPE(rela[i].r_info) != R_PPC_REL24)
+ continue;
+ /*
+ * reverse the operations in apply_relocate_add() for case
+ * R_PPC_REL24.
+ */
+ if (sym->st_shndx != SHN_UNDEF &&
+ sym->st_shndx != SHN_LIVEPATCH)
+ continue;
+
+ instruction = (u32 *)location;
+ if (is_mprofile_ftrace_call(symname))
+ continue;
+
+ if (!instr_is_relative_link_branch(*instruction))
+ continue;
+
+ instruction += 1;
+ *instruction = PPC_INST_NOP;
+ }
+
+}
+#endif
+
#ifdef CONFIG_DYNAMIC_FTRACE
int module_trampoline_target(struct module *mod, unsigned long addr,
unsigned long *target)
diff --git a/arch/s390/kernel/module.c b/arch/s390/kernel/module.c
index 2d159b32885b..cc6784fbc1ac 100644
--- a/arch/s390/kernel/module.c
+++ b/arch/s390/kernel/module.c
@@ -500,6 +500,14 @@ static int module_alloc_ftrace_hotpatch_trampolines(struct module *me,
}
#endif /* CONFIG_FUNCTION_TRACER */
+#ifdef CONFIG_LIVEPATCH
+void clear_relocate_add(Elf64_Shdr *sechdrs, const char *strtab,
+ unsigned int symindex, unsigned int relsec,
+ struct module *me)
+{
+}
+#endif
+
int module_finalize(const Elf_Ehdr *hdr,
const Elf_Shdr *sechdrs,
struct module *me)
diff --git a/arch/x86/kernel/module.c b/arch/x86/kernel/module.c
index b1abf663417c..f9632afbb84c 100644
--- a/arch/x86/kernel/module.c
+++ b/arch/x86/kernel/module.c
@@ -128,18 +128,20 @@ int apply_relocate(Elf32_Shdr *sechdrs,
return 0;
}
#else /*X86_64*/
-static int __apply_relocate_add(Elf64_Shdr *sechdrs,
+static int __apply_clear_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 clear)
{
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",
relsec, sechdrs[relsec].sh_info);
@@ -163,40 +165,60 @@ static int __apply_relocate_add(Elf64_Shdr *sechdrs,
case R_X86_64_NONE:
break;
case R_X86_64_64:
- if (*(u64 *)loc != 0)
- goto invalid_relocation;
- write(loc, &val, 8);
+ if (!clear) {
+ if (*(u64 *)loc != 0)
+ goto invalid_relocation;
+ write(loc, &val, 8);
+ } else {
+ write(loc, &zero, 8);
+ }
break;
case R_X86_64_32:
- if (*(u32 *)loc != 0)
- goto invalid_relocation;
- write(loc, &val, 4);
- if (val != *(u32 *)loc)
- goto overflow;
+ if (!clear) {
+ if (*(u32 *)loc != 0)
+ goto invalid_relocation;
+ write(loc, &val, 4);
+ if (val != *(u32 *)loc)
+ goto overflow;
+ } else {
+ write(loc, &zero, 4);
+ }
break;
case R_X86_64_32S:
- if (*(s32 *)loc != 0)
- goto invalid_relocation;
- write(loc, &val, 4);
- if ((s64)val != *(s32 *)loc)
- goto overflow;
+ if (!clear) {
+ if (*(s32 *)loc != 0)
+ goto invalid_relocation;
+ write(loc, &val, 4);
+ if ((s64)val != *(s32 *)loc)
+ goto overflow;
+ } else {
+ write(loc, &zero, 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);
+ if (!clear) {
+ if (*(u32 *)loc != 0)
+ goto invalid_relocation;
+ val -= (u64)loc;
+ write(loc, &val, 4);
#if 0
- if ((s64)val != *(s32 *)loc)
- goto overflow;
+ if ((s64)val != *(s32 *)loc)
+ goto overflow;
#endif
+ } else {
+ write(loc, &zero, 4);
+ }
break;
case R_X86_64_PC64:
- if (*(u64 *)loc != 0)
- goto invalid_relocation;
- val -= (u64)loc;
- write(loc, &val, 8);
+ if (!clear) {
+ if (*(u64 *)loc != 0)
+ goto invalid_relocation;
+ val -= (u64)loc;
+ write(loc, &val, 8);
+ } else {
+ write(loc, &zero, 8);
+ }
break;
default:
pr_err("%s: Unknown rela relocation: %llu\n",
@@ -234,8 +256,8 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
mutex_lock(&text_mutex);
}
- ret = __apply_relocate_add(sechdrs, strtab, symindex, relsec, me,
- write);
+ ret = __apply_clear_relocate_add(sechdrs, strtab, symindex, relsec, me,
+ write, false /* clear */);
if (!early) {
text_poke_sync();
@@ -245,6 +267,32 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
return ret;
}
+#ifdef CONFIG_LIVEPATCH
+
+void clear_relocate_add(Elf64_Shdr *sechdrs,
+ const char *strtab,
+ unsigned int symindex,
+ unsigned int relsec,
+ struct module *me)
+{
+ bool early = me->state == MODULE_STATE_UNFORMED;
+ void *(*write)(void *, const void *, size_t) = memcpy;
+
+ if (!early) {
+ write = text_poke;
+ mutex_lock(&text_mutex);
+ }
+
+ __apply_clear_relocate_add(sechdrs, strtab, symindex, relsec, me,
+ write, true /* clear */);
+
+ if (!early) {
+ text_poke_sync();
+ mutex_unlock(&text_mutex);
+ }
+}
+#endif
+
#endif
int module_finalize(const Elf_Ehdr *hdr,
diff --git a/include/linux/moduleloader.h b/include/linux/moduleloader.h
index 9e09d11ffe5b..d22b36b84b4b 100644
--- a/include/linux/moduleloader.h
+++ b/include/linux/moduleloader.h
@@ -72,6 +72,13 @@ int apply_relocate_add(Elf_Shdr *sechdrs,
unsigned int symindex,
unsigned int relsec,
struct module *mod);
+#ifdef CONFIG_LIVEPATCH
+void clear_relocate_add(Elf64_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 bc475e62279d..5c0d8a4eba13 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -316,6 +316,45 @@ int klp_apply_section_relocs(struct module *pmod, Elf_Shdr *sechdrs,
return apply_relocate_add(sechdrs, strtab, symndx, secndx, pmod);
}
+static void klp_clear_object_relocations(struct module *pmod,
+ struct klp_object *obj)
+{
+ int i, cnt;
+ const char *objname, *secname;
+ char sec_objname[MODULE_NAME_LEN];
+ Elf_Shdr *sec;
+
+ objname = klp_is_module(obj) ? obj->name : "vmlinux";
+
+ /* For each klp relocation section */
+ for (i = 1; i < pmod->klp_info->hdr.e_shnum; i++) {
+ sec = pmod->klp_info->sechdrs + i;
+ secname = pmod->klp_info->secstrings + sec->sh_name;
+ if (!(sec->sh_flags & SHF_RELA_LIVEPATCH))
+ continue;
+
+ /*
+ * Format: .klp.rela.sec_objname.section_name
+ * See comment in klp_resolve_symbols() for an explanation
+ * of the selected field width value.
+ */
+ secname = pmod->klp_info->secstrings + sec->sh_name;
+ cnt = sscanf(secname, ".klp.rela.%55[^.]", sec_objname);
+ if (cnt != 1) {
+ pr_err("section %s has an incorrectly formatted name\n",
+ secname);
+ continue;
+ }
+
+ if (strcmp(objname, sec_objname))
+ continue;
+
+ clear_relocate_add(pmod->klp_info->sechdrs,
+ pmod->core_kallsyms.strtab,
+ pmod->klp_info->symndx, i, pmod);
+ }
+}
+
/*
* Sysfs Interface
*
@@ -1154,7 +1193,7 @@ static void klp_cleanup_module_patches_limited(struct module *mod,
klp_unpatch_object(obj);
klp_post_unpatch_callback(obj);
-
+ klp_clear_object_relocations(patch->mod, obj);
klp_free_object_loaded(obj);
break;
}
--
2.30.2
