linux-kernel - [PATCH] kallsyms: strip LTO suffixes from static functions

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Date:   Tue, 22 Jun 2021 11:38:55 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        "KE . LI" <like1@...o.com>, Nathan Chancellor <nathan@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Miroslav Benes <mbenes@...e.cz>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Joe Perches <joe@...ches.com>, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com
Subject: [PATCH] kallsyms: strip LTO suffixes from static functions

Similar to:
commit 8b8e6b5d3b01 ("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.

Full LTO uses a different mangling scheme than thin LTO; full LTO
imports all code into effectively one big translation unit. It must
rename static functions to prevent collisions. Strip off these suffixes
so that we can continue to hook such static functions.

Reported-by: KE.LI(Lieke) <like1@...o.com>
Tested-by: KE.LI(Lieke) <like1@...o.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
---
 kernel/kallsyms.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index 4067564ec59f..14cf3a6474de 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -188,6 +188,24 @@ static inline bool cleanup_symbol_name(char *s)
 
 	return res != NULL;
 }
+#elif defined(CONFIG_LTO_CLANG_FULL)
+/*
+ * LLVM mangles static functions for full LTO so that two static functions with
+ * the same identifier do not collide when all code is combined into one
+ * module. The scheme used converts references to foo into
+ * foo.llvm.974640843467629774, for example. This can break hooking of static
+ * functions with kprobes.
+ */
+static inline bool cleanup_symbol_name(char *s)
+{
+	char *res;
+
+	res = strstr(s, ".llvm.");
+	if (res)
+		*res = '\0';
+
+	return res != NULL;
+}
 #else
 static inline bool cleanup_symbol_name(char *s) { return false; }
 #endif
-- 
2.32.0.288.g62a8d224e6-goog