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, or return back nops on powerpc). 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>
---
arch/powerpc/kernel/Makefile | 1 +
arch/powerpc/kernel/livepatch.c | 75 +++++++++++++++++++++++++++++++++
arch/powerpc/kernel/module.h | 15 +++++++
arch/powerpc/kernel/module_64.c | 7 +--
arch/x86/kernel/livepatch.c | 67 +++++++++++++++++++++++++++++
include/linux/livepatch.h | 5 +++
kernel/livepatch/core.c | 17 +++++---
7 files changed, 176 insertions(+), 11 deletions(-)
create mode 100644 arch/powerpc/kernel/livepatch.c
create mode 100644 arch/powerpc/kernel/module.h
diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
index 0ea6c4aa3a20..639000f78dc3 100644
--- a/arch/powerpc/kernel/Makefile
+++ b/arch/powerpc/kernel/Makefile
@@ -154,6 +154,7 @@ endif
obj-$(CONFIG_EPAPR_PARAVIRT) += epapr_paravirt.o epapr_hcalls.o
obj-$(CONFIG_KVM_GUEST) += kvm.o kvm_emul.o
+obj-$(CONFIG_LIVEPATCH) += livepatch.o
# Disable GCOV, KCOV & sanitizers in odd or sensitive code
GCOV_PROFILE_prom_init.o := n
diff --git a/arch/powerpc/kernel/livepatch.c b/arch/powerpc/kernel/livepatch.c
new file mode 100644
index 000000000000..6f2468c60695
--- /dev/null
+++ b/arch/powerpc/kernel/livepatch.c
@@ -0,0 +1,75 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * livepatch.c - powerpc-specific Kernel Live Patching Core
+ */
+
+#include <linux/livepatch.h>
+#include <asm/code-patching.h>
+#include "module.h"
+
+void arch_klp_free_object_loaded(struct klp_patch *patch,
+ struct klp_object *obj)
+{
+ const char *objname, *secname, *symname;
+ char sec_objname[MODULE_NAME_LEN];
+ struct klp_modinfo *info;
+ Elf64_Shdr *s;
+ Elf64_Rela *rel;
+ Elf64_Sym *sym;
+ void *loc;
+ u32 *instruction;
+ int i, cnt;
+
+ info = patch->mod->klp_info;
+ objname = klp_is_module(obj) ? obj->name : "vmlinux";
+
+ /* See livepatch core code for BUILD_BUG_ON() explanation */
+ BUILD_BUG_ON(MODULE_NAME_LEN < 56 || KSYM_NAME_LEN != 128);
+
+ /* For each klp relocation section */
+ for (s = info->sechdrs; s < info->sechdrs + info->hdr.e_shnum; s++) {
+ if (!(s->sh_flags & SHF_RELA_LIVEPATCH))
+ continue;
+
+ /*
+ * Format: .klp.rela.sec_objname.section_name
+ */
+ secname = info->secstrings + s->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;
+
+ rel = (void *)s->sh_addr;
+ for (i = 0; i < s->sh_size / sizeof(*rel); i++) {
+ loc = (void *)info->sechdrs[s->sh_info].sh_addr
+ + rel[i].r_offset;
+ sym = (Elf64_Sym *)info->sechdrs[info->symndx].sh_addr
+ + ELF64_R_SYM(rel[i].r_info);
+ symname = patch->mod->core_kallsyms.strtab
+ + sym->st_name;
+
+ if (ELF64_R_TYPE(rel[i].r_info) != R_PPC_REL24)
+ continue;
+
+ if (sym->st_shndx != SHN_UNDEF &&
+ sym->st_shndx != SHN_LIVEPATCH)
+ continue;
+
+ instruction = (u32 *)loc;
+ if (is_mprofile_mcount_callsite(symname, instruction))
+ continue;
+
+ if (!instr_is_relative_link_branch(*instruction))
+ continue;
+
+ instruction += 1;
+ *instruction = PPC_INST_NOP;
+ }
+ }
+}
diff --git a/arch/powerpc/kernel/module.h b/arch/powerpc/kernel/module.h
new file mode 100644
index 000000000000..748c38addf53
--- /dev/null
+++ b/arch/powerpc/kernel/module.h
@@ -0,0 +1,15 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+#ifndef _POWERPC_ARCH_MODULE_H
+#define _POWERPC_ARCH_MODULE_H
+
+#ifdef CONFIG_MPROFILE_KERNEL
+bool is_mprofile_mcount_callsite(const char *name, u32 *instruction);
+#else
+static inline bool is_mprofile_mcount_callsite(const char *name, u32 *instruction)
+{
+ return false;
+}
+#endif
+
+#endif
diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c
index a93b10c48000..5f34fbc3f1b8 100644
--- a/arch/powerpc/kernel/module_64.c
+++ b/arch/powerpc/kernel/module_64.c
@@ -450,7 +450,7 @@ static unsigned long stub_for_addr(const Elf64_Shdr *sechdrs,
}
#ifdef CONFIG_MPROFILE_KERNEL
-static bool is_mprofile_mcount_callsite(const char *name, u32 *instruction)
+bool is_mprofile_mcount_callsite(const char *name, u32 *instruction)
{
if (strcmp("_mcount", name))
return false;
@@ -485,11 +485,6 @@ static void squash_toc_save_inst(const char *name, unsigned long addr)
}
#else
static void squash_toc_save_inst(const char *name, unsigned long addr) { }
-
-static bool is_mprofile_mcount_callsite(const char *name, u32 *instruction)
-{
- return false;
-}
#endif
/* We expect a noop next: if it is, replace it with instruction to
diff --git a/arch/x86/kernel/livepatch.c b/arch/x86/kernel/livepatch.c
index 6a68e41206e7..e99bc8dbf4a7 100644
--- a/arch/x86/kernel/livepatch.c
+++ b/arch/x86/kernel/livepatch.c
@@ -51,3 +51,70 @@ void arch_klp_init_object_loaded(struct klp_patch *patch,
apply_paravirt(pseg, pseg + para->sh_size);
}
}
+
+void arch_klp_free_object_loaded(struct klp_patch *patch,
+ struct klp_object *obj)
+{
+ const char *objname, *secname;
+ char sec_objname[MODULE_NAME_LEN];
+ struct klp_modinfo *info;
+ Elf64_Shdr *s;
+ Elf64_Rela *rel;
+ void *loc;
+ int i, cnt;
+
+ info = patch->mod->klp_info;
+ objname = klp_is_module(obj) ? obj->name : "vmlinux";
+
+ /* See livepatch core code for BUILD_BUG_ON() explanation */
+ BUILD_BUG_ON(MODULE_NAME_LEN < 56 || KSYM_NAME_LEN != 128);
+
+ /* For each klp relocation section */
+ for (s = info->sechdrs; s < info->sechdrs + info->hdr.e_shnum; s++) {
+ if (!(s->sh_flags & SHF_RELA_LIVEPATCH))
+ continue;
+
+ /*
+ * Format: .klp.rela.sec_objname.section_name
+ */
+ secname = info->secstrings + s->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;
+
+ rel = (void *)s->sh_addr;
+ for (i = 0; i < s->sh_size / sizeof(*rel); i++) {
+ loc = (void *)info->sechdrs[s->sh_info].sh_addr
+ + rel[i].r_offset;
+
+ switch (ELF64_R_TYPE(rel[i].r_info)) {
+ case R_X86_64_NONE:
+ break;
+ case R_X86_64_64:
+ *(u64 *)loc = 0;
+ break;
+ case R_X86_64_32:
+ *(u32 *)loc = 0;
+ break;
+ case R_X86_64_32S:
+ *(s32 *)loc = 0;
+ break;
+ case R_X86_64_PC32:
+ case R_X86_64_PLT32:
+ *(u32 *)loc = 0;
+ break;
+ case R_X86_64_PC64:
+ *(u64 *)loc = 0;
+ break;
+ default:
+ break;
+ }
+ }
+ }
+}
diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h
index 273400814020..a227f473d5e5 100644
--- a/include/linux/livepatch.h
+++ b/include/linux/livepatch.h
@@ -202,6 +202,11 @@ static inline bool klp_have_reliable_stack(void)
IS_ENABLED(CONFIG_HAVE_RELIABLE_STACKTRACE);
}
+static inline bool klp_is_module(struct klp_object *obj)
+{
+ return obj->name;
+}
+
typedef int (*klp_shadow_ctor_t)(void *obj,
void *shadow_data,
void *ctor_data);
diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index ab4a4606d19b..7a5d0cd59ec1 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -43,11 +43,6 @@ LIST_HEAD(klp_patches);
static struct kobject *klp_root_kobj;
-static bool klp_is_module(struct klp_object *obj)
-{
- return obj->name;
-}
-
/* sets obj->mod if object is not vmlinux and module is found */
static void klp_find_object_module(struct klp_object *obj)
{
@@ -712,6 +707,12 @@ void __weak arch_klp_init_object_loaded(struct klp_patch *patch,
{
}
+/* Arches may override this to finish any remaining arch-specific tasks */
+void __weak arch_klp_free_object_loaded(struct klp_patch *patch,
+ struct klp_object *obj)
+{
+}
+
/* 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)
@@ -1100,6 +1101,12 @@ static void klp_cleanup_module_patches_limited(struct module *mod,
klp_post_unpatch_callback(obj);
+ mutex_lock(&text_mutex);
+ module_disable_ro(patch->mod);
+ arch_klp_free_object_loaded(patch, obj);
+ module_enable_ro(patch->mod, true);
+ mutex_unlock(&text_mutex);
+
klp_free_object_loaded(obj);
break;
}
--
2.22.0
