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objtool: Improve call destination function detection 

A recent clang change, combined with a binutils bug, can trigger a
situation where a ".Lprintk$local" STT_NOTYPE symbol gets created at the
same offset as the "printk" STT_FUNC symbol.  This confuses objtool:

  kernel/printk/printk.o: warning: objtool: ignore_loglevel_setup()+0x10: can't find call dest symbol at .text+0xc67

Improve the call destination detection by looking specifically for an
STT_FUNC symbol.

Reported-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Tested-by: Nathan Chancellor <natechancellor@gmail.com>
Link: https://github.com/ClangBuiltLinux/linux/issues/872
Link: https://sourceware.org/bugzilla/show_bug.cgi?id=25551
Link: https://lkml.kernel.org/r/0a7ee320bc0ea4469bd3dc450a7b4725669e0ea9.1581997059.git.jpoimboe@redhat.com
This commit is contained in:
Josh Poimboeuf 2020-02-17 21:41:54 -06:00 committed by Borislav Petkov
parent 113d4bc904
commit 7acfe53153
3 changed files with 31 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

27
tools/objtool/check.c
View File

@ -420,8 +420,8 @@ static void add_ignores(struct objtool_file *file)
break;
case STT_SECTION:
func = find_symbol_by_offset(rela->sym->sec, rela->addend);
if (!func || func->type != STT_FUNC)
func = find_func_by_offset(rela->sym->sec, rela->addend);
if (!func)
continue;
break;
@ -665,10 +665,14 @@ static int add_call_destinations(struct objtool_file *file)
insn->len);
if (!rela) {
dest_off = insn->offset + insn->len + insn->immediate;
insn->call_dest = find_symbol_by_offset(insn->sec,
dest_off);
insn->call_dest = find_func_by_offset(insn->sec, dest_off);
if (!insn->call_dest)
insn->call_dest = find_symbol_by_offset(insn->sec, dest_off);
if (!insn->call_dest && !insn->ignore) {
if (insn->ignore)
continue;
if (!insn->call_dest) {
WARN_FUNC("unsupported intra-function call",
insn->sec, insn->offset);
if (retpoline)
@ -676,11 +680,16 @@ static int add_call_destinations(struct objtool_file *file)
return -1;
}
if (insn->func && insn->call_dest->type != STT_FUNC) {
WARN_FUNC("unsupported call to non-function",
insn->sec, insn->offset);
return -1;
}
} else if (rela->sym->type == STT_SECTION) {
insn->call_dest = find_symbol_by_offset(rela->sym->sec,
rela->addend+4);
if (!insn->call_dest ||
insn->call_dest->type != STT_FUNC) {
insn->call_dest = find_func_by_offset(rela->sym->sec,
rela->addend+4);
if (!insn->call_dest) {
WARN_FUNC("can't find call dest symbol at %s+0x%x",
insn->sec, insn->offset,
rela->sym->sec->name,

14
tools/objtool/elf.c
View File

@ -62,8 +62,18 @@ struct symbol *find_symbol_by_offset(struct section *sec, unsigned long offset)
struct symbol *sym;
list_for_each_entry(sym, &sec->symbol_list, list)
if (sym->type != STT_SECTION &&
sym->offset == offset)
if (sym->type != STT_SECTION && sym->offset == offset)
return sym;
return NULL;
}
struct symbol *find_func_by_offset(struct section *sec, unsigned long offset)
{
struct symbol *sym;
list_for_each_entry(sym, &sec->symbol_list, list)
if (sym->type == STT_FUNC && sym->offset == offset)
return sym;
return NULL;

1
tools/objtool/elf.h
View File

@ -77,6 +77,7 @@ struct elf {
struct elf *elf_read(const char *name, int flags);
struct section *find_section_by_name(struct elf *elf, const char *name);
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(struct elf *elf, const char *name);
struct symbol *find_symbol_containing(struct section *sec, unsigned long offset);