[PATCH v4 07/17] kallsyms: strip ThinLTO hashes from static functions

[Sami Tolvanen]

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 <ja...@codeaurora.org>
Signed-off-by: Sami Tolvanen <samitolva...@google.com>
Reviewed-by: Kees Cook <keesc...@chromium.org>
---
 kernel/kallsyms.c | 55 ++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 50 insertions(+), 5 deletions(-)

diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index 8043a90aa50e..c851ca0ed357 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -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. */
-- 
2.31.0.291.g576ba9dcdaf-goog