Commit 8b8e6b5d authored by Sami Tolvanen's avatar Sami Tolvanen Committed by Kees Cook
Browse files

kallsyms: strip ThinLTO hashes from static functions 



With CONFIG_CFI_CLANG and ThinLTO, Clang appends a hash to the names
of all static functions not marked __used. This can break userspace
tools that don't expect the function name to change, so strip out the
hash from the output.

Suggested-by: default avatarJack Pham <jackp@codeaurora.org>
Signed-off-by: default avatarSami Tolvanen <samitolvanen@google.com>
Reviewed-by: default avatarKees Cook <keescook@chromium.org>
Tested-by: default avatarNathan Chancellor <nathan@kernel.org>
Signed-off-by: default avatarKees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20210408182843.1754385-8-samitolvanen@google.com
parent 0a5b4128

kernel/kallsyms.c

+50 −5
Original line number Diff line number Diff line
@@ -161,6 +161,27 @@ static unsigned long kallsyms_sym_address(int idx) 
	return kallsyms_relative_base - 1 - kallsyms_offsets[idx];

}



#if defined(CONFIG_CFI_CLANG) && defined(CONFIG_LTO_CLANG_THIN)

/*

 * LLVM appends a hash to static function names when ThinLTO and CFI are

 * both enabled, i.e. foo() becomes foo$707af9a22804d33c81801f27dcfe489b.

 * This causes confusion and potentially breaks user space tools, so we

 * strip the suffix from expanded symbol names.

 */

static inline bool cleanup_symbol_name(char *s)

{

	char *res;



	res = strrchr(s, '$');

	if (res)

		*res = '\0';



	return res != NULL;

}

#else

static inline bool cleanup_symbol_name(char *s) { return false; }

#endif



/* Lookup the address for this symbol. Returns 0 if not found. */

unsigned long kallsyms_lookup_name(const char *name)

{
@@ -173,6 +194,9 @@ unsigned long kallsyms_lookup_name(const char *name) 


		if (strcmp(namebuf, name) == 0)

			return kallsyms_sym_address(i);



		if (cleanup_symbol_name(namebuf) && strcmp(namebuf, name) == 0)

			return kallsyms_sym_address(i);

	}

	return module_kallsyms_lookup_name(name);

}
@@ -303,7 +327,9 @@ const char *kallsyms_lookup(unsigned long addr, 
				       namebuf, KSYM_NAME_LEN);

		if (modname)

			*modname = NULL;

		return namebuf;



		ret = namebuf;

		goto found;

	}



	/* See if it's in a module or a BPF JITed image. */
@@ -316,11 +342,16 @@ const char *kallsyms_lookup(unsigned long addr, 
	if (!ret)

		ret = ftrace_mod_address_lookup(addr, symbolsize,

						offset, modname, namebuf);



found:

	cleanup_symbol_name(namebuf);

	return ret;

}



int lookup_symbol_name(unsigned long addr, char *symname)

{

	int res;



	symname[0] = '\0';

	symname[KSYM_NAME_LEN - 1] = '\0';
@@ -331,15 +362,23 @@ int lookup_symbol_name(unsigned long addr, char *symname) 
		/* Grab name */

		kallsyms_expand_symbol(get_symbol_offset(pos),

				       symname, KSYM_NAME_LEN);

		return 0;

		goto found;

	}

	/* See if it's in a module. */

	return lookup_module_symbol_name(addr, symname);

	res = lookup_module_symbol_name(addr, symname);

	if (res)

		return res;



found:

	cleanup_symbol_name(symname);

	return 0;

}



int lookup_symbol_attrs(unsigned long addr, unsigned long *size,

			unsigned long *offset, char *modname, char *name)

{

	int res;



	name[0] = '\0';

	name[KSYM_NAME_LEN - 1] = '\0';
@@ -351,10 +390,16 @@ int lookup_symbol_attrs(unsigned long addr, unsigned long *size, 
		kallsyms_expand_symbol(get_symbol_offset(pos),

				       name, KSYM_NAME_LEN);

		modname[0] = '\0';

		return 0;

		goto found;

	}

	/* See if it's in a module. */

	return lookup_module_symbol_attrs(addr, size, offset, modname, name);

	res = lookup_module_symbol_attrs(addr, size, offset, modname, name);

	if (res)

		return res;



found:

	cleanup_symbol_name(name);

	return 0;

}



/* Look up a kernel symbol and return it in a text buffer. */