[RFC PATCH 16/21] objtool: Add support for CONFIG_CFI_CLANG

Sami Tolvanen
2022-04-29T20:37:26Z

With -fsanitize=kcfi, the compiler injects a type identifier before
each function. Teach objtool to recognize the identifier.

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
---
scripts/Makefile.build | 3 +-
scripts/link-vmlinux.sh | 3 +
tools/objtool/arch/x86/include/arch/elf.h | 2 +
tools/objtool/builtin-check.c | 3 +-
tools/objtool/check.c | 128 ++++++++++++++++++++--
tools/objtool/elf.c | 13 +++
tools/objtool/include/objtool/arch.h | 1 +
tools/objtool/include/objtool/builtin.h | 2 +-
tools/objtool/include/objtool/elf.h | 2 +
9 files changed, 145 insertions(+), 12 deletions(-)

diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 9717e6f6fb31..c850ac420b60 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -235,7 +235,8 @@ objtool_args = \
$(if $(CONFIG_RETPOLINE), --retpoline) \
$(if $(CONFIG_X86_SMAP), --uaccess) \
$(if $(CONFIG_FTRACE_MCOUNT_USE_OBJTOOL), --mcount) \
- $(if $(CONFIG_SLS), --sls)
+ $(if $(CONFIG_SLS), --sls) \
+ $(if $(CONFIG_CFI_CLANG), --kcfi)

cmd_objtool = $(if $(objtool-enabled), ; $(objtool) $(objtool_args) $@)
cmd_gen_objtooldep = $(if $(objtool-enabled), { echo ; echo '$@: $$(wildcard $(objtool))' ; } >> $(dot-target).cmd)
diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index 20f44504a644..d171f8507db2 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -152,6 +152,9 @@ objtool_link()
if is_enabled CONFIG_SLS; then
objtoolopt="${objtoolopt} --sls"
fi
+ if is_enabled CONFIG_CFI_CLANG; then
+ objtoolopt="${objtoolopt} --kcfi"
+ fi
info OBJTOOL ${1}
tools/objtool/objtool ${objtoolcmd} ${objtoolopt} ${1}
fi
diff --git a/tools/objtool/arch/x86/include/arch/elf.h b/tools/objtool/arch/x86/include/arch/elf.h
index 69cc4264b28a..8833d989eec7 100644
--- a/tools/objtool/arch/x86/include/arch/elf.h
+++ b/tools/objtool/arch/x86/include/arch/elf.h
@@ -3,4 +3,6 @@

#define R_NONE R_X86_64_NONE

+#define KCFI_TYPEID_LEN 6
+
#endif /* _OBJTOOL_ARCH_ELF */
diff --git a/tools/objtool/builtin-check.c b/tools/objtool/builtin-check.c
index fc6975ab8b06..8a662dcc21be 100644
--- a/tools/objtool/builtin-check.c
+++ b/tools/objtool/builtin-check.c
@@ -21,7 +21,7 @@

bool no_fp, no_unreachable, retpoline, module, backtrace, uaccess, stats,
lto, vmlinux, mcount, noinstr, backup, sls, dryrun,
- ibt;
+ ibt, kcfi;

static const char * const check_usage[] = {
"objtool check [<options>] file.o",
@@ -49,6 +49,7 @@ const struct option check_options[] = {
OPT_BOOLEAN('S', "sls", &sls, "validate straight-line-speculation"),
OPT_BOOLEAN(0, "dry-run", &dryrun, "don't write the modifications"),
OPT_BOOLEAN(0, "ibt", &ibt, "validate ENDBR placement"),
+ OPT_BOOLEAN('k', "kcfi", &kcfi, "detect control-flow integrity type identifiers"),
OPT_END(),
};

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index bd0c2c828940..e6bee2f2996a 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -27,6 +27,12 @@ struct alternative {
bool skip_orig;
};

+struct kcfi_type {
+ struct section *sec;
+ unsigned long offset;
+ struct hlist_node hash;
+};
+
static unsigned long nr_cfi, nr_cfi_reused, nr_cfi_cache;

static struct cfi_init_state initial_func_cfi;
@@ -143,6 +149,99 @@ static bool is_sibling_call(struct instruction *insn)
return (is_static_jump(insn) && insn->call_dest);
}

+static int kcfi_bits;
+static struct hlist_head *kcfi_hash;
+
+static void *kcfi_alloc_hash(unsigned long size)
+{
+ kcfi_bits = max(10, ilog2(size));
+ kcfi_hash = mmap(NULL, sizeof(struct hlist_head) << kcfi_bits,
+ PROT_READ|PROT_WRITE,
+ MAP_PRIVATE|MAP_ANON, -1, 0);
+ if (kcfi_hash == (void *)-1L) {
+ WARN("mmap fail kcfi_hash");
+ kcfi_hash = NULL;
+ } else if (stats) {
+ printf("kcfi_bits: %d\n", kcfi_bits);
+ }
+
+ return kcfi_hash;
+}
+
+static void add_kcfi_type(struct kcfi_type *type)
+{
+ hlist_add_head(&type->hash,
+ &kcfi_hash[hash_min(
+ sec_offset_hash(type->sec, type->offset),
+ kcfi_bits)]);
+}
+
+static bool add_kcfi_types(struct section *sec)
+{
+ struct reloc *reloc;
+
+ list_for_each_entry(reloc, &sec->reloc_list, list) {
+ struct kcfi_type *type;
+
+ if (reloc->sym->type != STT_SECTION) {
+ WARN("unexpected relocation symbol type in %s", sec->name);
+ return false;
+ }
+
+ type = malloc(sizeof(*type));
+ if (!type) {
+ perror("malloc");
+ return false;
+ }
+
+ type->sec = reloc->sym->sec;
+ type->offset = reloc->addend;
+
+ add_kcfi_type(type);
+ }
+
+ return true;
+}
+
+static int read_kcfi_types(struct objtool_file *file)
+{
+ if (!kcfi)
+ return 0;
+
+ if (!kcfi_alloc_hash(file->elf->text_size / 16))
+ return -1;
+
+ if (!for_each_section_by_name(file->elf, ".rela.kcfi_types", add_kcfi_types))
+ return -1;
+
+ return 0;
+}
+
+static bool is_kcfi_typeid(struct elf *elf, struct instruction *insn)
+{
+ struct hlist_head *head;
+ struct kcfi_type *type;
+ struct reloc *reloc;
+
+ if (!kcfi)
+ return false;
+
+ /* Compiler-generated annotation in .kcfi_types. */
+ head = &kcfi_hash[hash_min(sec_offset_hash(insn->sec, insn->offset), kcfi_bits)];
+
+ hlist_for_each_entry(type, head, hash)
+ if (type->sec == insn->sec && type->offset == insn->offset)
+ return true;
+
+ /* Manual annotation (in assembly code). */
+ reloc = find_reloc_by_dest(elf, insn->sec, insn->offset);
+
+ if (reloc && !strncmp(reloc->sym->name, "__kcfi_typeid_", 14))
+ return true;
+
+ return false;
+}
+
/*
* This checks to see if the given function is a "noreturn" function.
*
@@ -388,13 +487,18 @@ static int decode_instructions(struct objtool_file *file)
insn->sec = sec;
insn->offset = offset;

- ret = arch_decode_instruction(file, sec, offset,
- sec->sh.sh_size - offset,
- &insn->len, &insn->type,
- &insn->immediate,
- &insn->stack_ops);
- if (ret)
- goto err;
+ if (is_kcfi_typeid(file->elf, insn)) {
+ insn->type = INSN_KCFI_TYPEID;
+ insn->len = KCFI_TYPEID_LEN;
+ } else {
+ ret = arch_decode_instruction(file, sec, offset,
+ sec->sh.sh_size - offset,
+ &insn->len, &insn->type,
+ &insn->immediate,
+ &insn->stack_ops);
+ if (ret)
+ goto err;
+ }

/*
* By default, "ud2" is a dead end unless otherwise
@@ -420,7 +524,8 @@ static int decode_instructions(struct objtool_file *file)
}

sym_for_each_insn(file, func, insn) {
- insn->func = func;
+ if (insn->type != INSN_KCFI_TYPEID)
+ insn->func = func;
if (insn->type == INSN_ENDBR && list_empty(&insn->call_node)) {
if (insn->offset == insn->func->offset) {
list_add_tail(&insn->call_node, &file->endbr_list);
@@ -2219,6 +2324,10 @@ static int decode_sections(struct objtool_file *file)
if (ret)
return ret;

+ ret = read_kcfi_types(file);
+ if (ret)
+ return ret;
+
ret = decode_instructions(file);
if (ret)
return ret;
@@ -3595,7 +3704,8 @@ static bool ignore_unreachable_insn(struct objtool_file *file, struct instructio
int i;
struct instruction *prev_insn;

- if (insn->ignore || insn->type == INSN_NOP || insn->type == INSN_TRAP)
+ if (insn->ignore || insn->type == INSN_NOP || insn->type == INSN_TRAP ||
+ insn->type == INSN_KCFI_TYPEID)
return true;

/*
diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index d7b99a737496..c4e277d41fd2 100644
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -120,6 +120,19 @@ struct section *find_section_by_name(const struct elf *elf, const char *name)
return NULL;
}

+bool for_each_section_by_name(const struct elf *elf, const char *name,
+ bool (*callback)(struct section *))
+{
+ struct section *sec;
+
+ elf_hash_for_each_possible(section_name, sec, name_hash, str_hash(name)) {
+ if (!strcmp(sec->name, name) && !callback(sec))
+ return false;
+ }
+
+ return true;
+}
+
static struct section *find_section_by_index(struct elf *elf,
unsigned int idx)
{
diff --git a/tools/objtool/include/objtool/arch.h b/tools/objtool/include/objtool/arch.h
index 9b19cc304195..3db5951e7aa9 100644
--- a/tools/objtool/include/objtool/arch.h
+++ b/tools/objtool/include/objtool/arch.h
@@ -28,6 +28,7 @@ enum insn_type {
INSN_CLD,
INSN_TRAP,
INSN_ENDBR,
+ INSN_KCFI_TYPEID,
INSN_OTHER,
};

diff --git a/tools/objtool/include/objtool/builtin.h b/tools/objtool/include/objtool/builtin.h
index c39dbfaef6dc..68409070bca5 100644
--- a/tools/objtool/include/objtool/builtin.h
+++ b/tools/objtool/include/objtool/builtin.h
@@ -10,7 +10,7 @@
extern const struct option check_options[];
extern bool no_fp, no_unreachable, retpoline, module, backtrace, uaccess, stats,
lto, vmlinux, mcount, noinstr, backup, sls, dryrun,
- ibt;
+ ibt, kcfi;

extern int cmd_parse_options(int argc, const char **argv, const char * const usage[]);

diff --git a/tools/objtool/include/objtool/elf.h b/tools/objtool/include/objtool/elf.h
index 22ba7e2b816e..7fd3462ce32a 100644
--- a/tools/objtool/include/objtool/elf.h
+++ b/tools/objtool/include/objtool/elf.h
@@ -148,6 +148,8 @@ int elf_write(struct elf *elf);
void elf_close(struct elf *elf);

struct section *find_section_by_name(const struct elf *elf, const char *name);
+bool for_each_section_by_name(const struct elf *elf, const char *name,
+ bool (*callback)(struct section *));
struct symbol *find_func_by_offset(struct section *sec, unsigned long offset);
struct symbol *find_symbol_by_offset(struct section *sec, unsigned long offset);
struct symbol *find_symbol_by_name(const struct elf *elf, const char *name);
--
2.36.0.464.gb9c8b46e94-goog