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Date: Thu, 21 Jul 2022 10:51:47 -0700
From: Song Liu <song@...nel.org>
To: <live-patching@...r.kernel.org>, <linux-kernel@...r.kernel.org>
CC: <jpoimboe@...nel.org>, <jikos@...nel.org>, <mbenes@...e.cz>,
<pmladek@...e.com>, <joe.lawrence@...hat.com>, <x86@...nel.org>,
Josh Poimboeuf <jpoimboe@...hat.com>,
Song Liu <song@...nel.org>
Subject: [PATCH v3] livepatch: Clear relocation targets on a module removal
From: Miroslav Benes <mbenes@...e.cz>
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@...hat.com>
Signed-off-by: Miroslav Benes <mbenes@...e.cz>
Signed-off-by: Song Liu <song@...nel.org>
---
Changes from v2:
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@suse.cz/T/#u
---
arch/powerpc/kernel/module_64.c | 10 ++++
arch/s390/kernel/module.c | 8 ++++
arch/x86/kernel/module.c | 85 +++++++++++++++++++++++++++++++++
include/linux/moduleloader.h | 7 +++
kernel/livepatch/core.c | 41 +++++++++++++++-
5 files changed, 150 insertions(+), 1 deletion(-)
diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c
index 7e45dc98df8a..9125f0aff5d4 100644
--- a/arch/powerpc/kernel/module_64.c
+++ b/arch/powerpc/kernel/module_64.c
@@ -739,6 +739,16 @@ 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)
+{
+}
+#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 26125a9c436d..abbf45715354 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 67828d973389..2e4f219ea98b 100644
--- a/arch/x86/kernel/module.c
+++ b/arch/x86/kernel/module.c
@@ -245,6 +245,91 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
return ret;
}
+#ifdef CONFIG_LIVEPATCH
+
+static void __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))
+{
+ unsigned int i;
+ Elf64_Rela *rel = (void *)sechdrs[relsec].sh_addr;
+ Elf64_Sym *sym;
+ void *loc;
+ u64 zero_u64 = 0ULL;
+ u32 zero_u32 = 0;
+
+ DEBUGP("Clearing relocate section %u to %u\n",
+ relsec, sechdrs[relsec].sh_info);
+ for (i = 0; i < sechdrs[relsec].sh_size / sizeof(*rel); i++) {
+ /* This is where to make the change */
+ loc = (void *)sechdrs[sechdrs[relsec].sh_info].sh_addr
+ + rel[i].r_offset;
+
+ /*
+ * This is the symbol it is referring to. Note that all
+ * undefined symbols have been resolved.
+ */
+ sym = (Elf64_Sym *)sechdrs[symindex].sh_addr
+ + ELF64_R_SYM(rel[i].r_info);
+
+ DEBUGP("type %d st_value %Lx r_addend %Lx loc %Lx\n",
+ (int)ELF64_R_TYPE(rel[i].r_info),
+ sym->st_value, rel[i].r_addend, (u64)loc);
+
+ switch (ELF64_R_TYPE(rel[i].r_info)) {
+ case R_X86_64_NONE:
+ break;
+ case R_X86_64_64:
+ write(loc, &zero_u64, 8);
+ break;
+ case R_X86_64_32:
+ write(loc, &zero_u32, 4);
+ break;
+ case R_X86_64_32S:
+ write(loc, &zero_u32, 4);
+ break;
+ case R_X86_64_PC32:
+ case R_X86_64_PLT32:
+ write(loc, &zero_u32, 4);
+ break;
+ case R_X86_64_PC64:
+ write(loc, &zero_u64, 8);
+ break;
+ default:
+ pr_err("%s: Unknown rela relocation: %llu\n",
+ me->name, ELF64_R_TYPE(rel[i].r_info));
+ break;
+ }
+ }
+}
+
+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);
+ }
+
+ __clear_relocate_add(sechdrs, strtab, symindex, relsec, me,
+ write);
+
+ 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
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