Commit fb6a421f authored by Song Liu's avatar Song Liu Committed by Kees Cook
Browse files

kallsyms: Match symbols exactly with CONFIG_LTO_CLANG 



With CONFIG_LTO_CLANG=y, the compiler may add .llvm.<hash> suffix to
function names to avoid duplication. APIs like kallsyms_lookup_name()
and kallsyms_on_each_match_symbol() tries to match these symbol names
without the .llvm.<hash> suffix, e.g., match "c_stop" with symbol
c_stop.llvm.17132674095431275852. This turned out to be problematic
for use cases that require exact match, for example, livepatch.

Fix this by making the APIs to match symbols exactly.

Also cleanup kallsyms_selftests accordingly.

Signed-off-by: default avatarSong Liu <song@kernel.org>
Fixes: 8cc32a9b ("kallsyms: strip LTO-only suffixes from promoted global functions")
Tested-by: default avatarMasami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: default avatarMasami Hiramatsu (Google) <mhiramat@kernel.org>
Acked-by: default avatarPetr Mladek <pmladek@suse.com>
Reviewed-by: default avatarSami Tolvanen <samitolvanen@google.com>
Reviewed-by: default avatarLuis Chamberlain <mcgrof@kernel.org>
Link: https://lore.kernel.org/r/20240807220513.3100483-3-song@kernel.org


Signed-off-by: default avatarKees Cook <kees@kernel.org>
parent 020925ce

kernel/kallsyms.c

+6 −49
Original line number Diff line number Diff line
@@ -160,38 +160,6 @@ unsigned long kallsyms_sym_address(int idx) 
	return kallsyms_relative_base - 1 - kallsyms_offsets[idx];

}



static void cleanup_symbol_name(char *s)

{

	char *res;



	if (!IS_ENABLED(CONFIG_LTO_CLANG))

		return;



	/*

	 * LLVM appends various suffixes for local functions and variables that

	 * must be promoted to global scope as part of LTO.  This can break

	 * hooking of static functions with kprobes. '.' is not a valid

	 * character in an identifier in C. Suffixes only in LLVM LTO observed:

	 * - foo.llvm.[0-9a-f]+

	 */

	res = strstr(s, ".llvm.");

	if (res)

		*res = '\0';



	return;

}



static int compare_symbol_name(const char *name, char *namebuf)

{

	/* The kallsyms_seqs_of_names is sorted based on names after

	 * cleanup_symbol_name() (see scripts/kallsyms.c) if clang lto is enabled.

	 * To ensure correct bisection in kallsyms_lookup_names(), do

	 * cleanup_symbol_name(namebuf) before comparing name and namebuf.

	 */

	cleanup_symbol_name(namebuf);

	return strcmp(name, namebuf);

}



static unsigned int get_symbol_seq(int index)

{

	unsigned int i, seq = 0;
@@ -219,7 +187,7 @@ static int kallsyms_lookup_names(const char *name, 
		seq = get_symbol_seq(mid);

		off = get_symbol_offset(seq);

		kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf));

		ret = compare_symbol_name(name, namebuf);

		ret = strcmp(name, namebuf);

		if (ret > 0)

			low = mid + 1;

		else if (ret < 0)
@@ -236,7 +204,7 @@ static int kallsyms_lookup_names(const char *name, 
		seq = get_symbol_seq(low - 1);

		off = get_symbol_offset(seq);

		kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf));

		if (compare_symbol_name(name, namebuf))

		if (strcmp(name, namebuf))

			break;

		low--;

	}
@@ -248,7 +216,7 @@ static int kallsyms_lookup_names(const char *name, 
			seq = get_symbol_seq(high + 1);

			off = get_symbol_offset(seq);

			kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf));

			if (compare_symbol_name(name, namebuf))

			if (strcmp(name, namebuf))

				break;

			high++;

		}
@@ -407,8 +375,7 @@ static int kallsyms_lookup_buildid(unsigned long addr, 
		if (modbuildid)

			*modbuildid = NULL;



		ret = strlen(namebuf);

		goto found;

		return strlen(namebuf);

	}



	/* See if it's in a module or a BPF JITed image. */
@@ -422,8 +389,6 @@ static int kallsyms_lookup_buildid(unsigned long addr, 
		ret = ftrace_mod_address_lookup(addr, symbolsize,

						offset, modname, namebuf);



found:

	cleanup_symbol_name(namebuf);

	return ret;

}
@@ -450,8 +415,6 @@ const char *kallsyms_lookup(unsigned long addr, 


int lookup_symbol_name(unsigned long addr, char *symname)

{

	int res;



	symname[0] = '\0';

	symname[KSYM_NAME_LEN - 1] = '\0';
@@ -462,16 +425,10 @@ int lookup_symbol_name(unsigned long addr, char *symname) 
		/* Grab name */

		kallsyms_expand_symbol(get_symbol_offset(pos),

				       symname, KSYM_NAME_LEN);

		goto found;

		return 0;

	}

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

	res = lookup_module_symbol_name(addr, symname);

	if (res)

		return res;



found:

	cleanup_symbol_name(symname);

	return 0;

	return lookup_module_symbol_name(addr, symname);

}



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

kernel/kallsyms_selftest.c

+1 −21
Original line number Diff line number Diff line
@@ -187,31 +187,11 @@ static void test_perf_kallsyms_lookup_name(void) 
		stat.min, stat.max, div_u64(stat.sum, stat.real_cnt));

}



static bool match_cleanup_name(const char *s, const char *name)

{

	char *p;

	int len;



	if (!IS_ENABLED(CONFIG_LTO_CLANG))

		return false;



	p = strstr(s, ".llvm.");

	if (!p)

		return false;



	len = strlen(name);

	if (p - s != len)

		return false;



	return !strncmp(s, name, len);

}



static int find_symbol(void *data, const char *name, unsigned long addr)

{

	struct test_stat *stat = (struct test_stat *)data;



	if (strcmp(name, stat->name) == 0 ||

	    (!stat->perf && match_cleanup_name(name, stat->name))) {

	if (!strcmp(name, stat->name)) {

		stat->real_cnt++;

		stat->addr = addr;