kallsyms: strip LTO suffixes from static functions

Similar to:
commit 8b8e6b5 ("kallsyms: strip ThinLTO hashes from static
functions")

It's very common for compilers to modify the symbol name for static
functions as part of optimizing transformations. That makes hooking
static functions (that weren't inlined or DCE'd) with kprobes difficult.

LLVM has yet another name mangling scheme used by thin LTO.

Combine handling of the various schemes by truncating after the first
'.'.  Strip off these suffixes so that we can continue to hook such
static functions.  Clang releases prior to clang-13 would use '$'
instead of '.'

Link: https://reviews.llvm.org/rGc6e5c4654bd5045fe22a1a52779e48e2038a404c
Reported-by: KE.LI(Lieke) <[email protected]>
Suggested-by: Nathan Chancellor <[email protected]>
Suggested-by: Padmanabha Srinivasaiah <[email protected]>
Suggested-by: Sami Tolvanen <[email protected]>
Reviewed-by: Nathan Chancellor <[email protected]>
Reviewed-by: Fangrui Song <[email protected]>
Reviewed-by: Sami Tolvanen <[email protected]>
Signed-off-by: Nick Desaulniers <[email protected]>
Signed-off-by: Kees Cook <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

Author: nickdesaulniers

kernel/kallsyms.c

@@ -164,26 +164,46 @@ 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)
+static bool cleanup_symbol_name(char *s)
 {
 	char *res;
 
+	if (!IS_ENABLED(CONFIG_LTO_CLANG))
+		return false;
+
+	/*
+	 * 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 observed:
+	 * - foo.llvm.[0-9a-f]+
+	 * - foo.[0-9a-f]+
+	 * - foo.[0-9a-f]+.cfi_jt
+	 */
+	res = strchr(s, '.');
+	if (res) {
+		*res = '\0';
+		return true;
+	}
+
+	if (!IS_ENABLED(CONFIG_CFI_CLANG) ||
+	    !IS_ENABLED(CONFIG_LTO_CLANG_THIN) ||
+	    CONFIG_CLANG_VERSION >= 130000)
+		return false;
+
+	/*
+	 * Prior to LLVM 13, the following suffixes were observed when thinLTO
+	 * and CFI are both enabled:
+	 * - foo$[0-9]+
+	 */
 	res = strrchr(s, '$');
-	if (res)
+	if (res) {
 		*res = '\0';
+		return true;
+	}
 
-	return res != NULL;
+	return false;
 }
-#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)