[PATCH 07/17] kallsyms: cfi: strip hashes from static functions

Sami Tolvanen
2021-03-12T00:50:21Z

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: Jack Pham <jackp@codeaurora.org>
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
---
kernel/kallsyms.c | 54 ++++++++++++++++++++++++++++++++++++++++++-----
1 file changed, 49 insertions(+), 5 deletions(-)

diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index 8043a90aa50e..17d3a704bafa 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -161,6 +161,26 @@ 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, which causes confusion and potentially breaks user space
+ * tools, so we will strip the postfix from expanded symbol names.
+ */
+static inline char *cleanup_symbol_name(char *s)
+{
+ char *res = NULL;
+
+ res = strrchr(s, '$');
+ if (res)
+ *res = '\0';
+
+ return res;
+}
+#else
+static inline char *cleanup_symbol_name(char *s) { return NULL; }
+#endif
+
/* Lookup the address for this symbol. Returns 0 if not found. */
unsigned long kallsyms_lookup_name(const char *name)
{
@@ -173,6 +193,9 @@ 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 +326,9 @@ 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 +341,16 @@ 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 +361,23 @@ 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 +389,16 @@ 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. */
--
2.31.0.rc2.261.g7f71774620-goog