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kallsyms: Match symbols exactly with CONFIG_LTO_CLANG

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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: Song Liu <song@kernel.org>
Fixes: 8cc32a9bbf ("kallsyms: strip LTO-only suffixes from promoted global functions")
Tested-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Acked-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
Link: https://lore.kernel.org/r/20240807220513.3100483-3-song@kernel.org
Signed-off-by: Kees Cook <kees@kernel.org>
This commit is contained in:
Song Liu 2024-08-07 15:05:13 -07:00 committed by Kees Cook
parent 020925ce92
commit fb6a421fb6
2 changed files with 7 additions and 70 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

55
kernel/kallsyms.c
View File

@ -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. */

22
kernel/kallsyms_selftest.c
View File

@ -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;