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authorYonghong Song <yhs@fb.com>2023-06-28 11:19:26 -0700
committerKees Cook <keescook@chromium.org>2023-07-12 15:39:34 -0700
commit8cc32a9bbf2934d90762d9de0187adcb5ad46a11 (patch)
tree3cd33822bdd02e39c736b89063566a4807dfdfd8
parent5fc52248559802f0f1ac10b3c8729a1568216715 (diff)
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kallsyms: strip LTO-only suffixes from promoted global functions
Commit 6eb4bd92c1ce ("kallsyms: strip LTO suffixes from static functions") stripped all function/variable suffixes started with '.' regardless of whether those suffixes are generated at LTO mode or not. In fact, as far as I know, in LTO mode, when a static function/variable is promoted to the global scope, '.llvm.<...>' suffix is added. The existing mechanism breaks live patch for a LTO kernel even if no <symbol>.llvm.<...> symbols are involved. For example, for the following kernel symbols: $ grep bpf_verifier_vlog /proc/kallsyms ffffffff81549f60 t bpf_verifier_vlog ffffffff8268b430 d bpf_verifier_vlog._entry ffffffff8282a958 d bpf_verifier_vlog._entry_ptr ffffffff82e12a1f d bpf_verifier_vlog.__already_done 'bpf_verifier_vlog' is a static function. '_entry', '_entry_ptr' and '__already_done' are static variables used inside 'bpf_verifier_vlog', so llvm promotes them to file-level static with prefix 'bpf_verifier_vlog.'. Note that the func-level to file-level static function promotion also happens without LTO. Given a symbol name 'bpf_verifier_vlog', with LTO kernel, current mechanism will return 4 symbols to live patch subsystem which current live patching subsystem cannot handle it. With non-LTO kernel, only one symbol is returned. In [1], we have a lengthy discussion, the suggestion is to separate two cases: (1). new symbols with suffix which are generated regardless of whether LTO is enabled or not, and (2). new symbols with suffix generated only when LTO is enabled. The cleanup_symbol_name() should only remove suffixes for case (2). Case (1) should not be changed so it can work uniformly with or without LTO. This patch removed LTO-only suffix '.llvm.<...>' so live patching and tracing should work the same way for non-LTO kernel. The cleanup_symbol_name() in scripts/kallsyms.c is also changed to have the same filtering pattern so both kernel and kallsyms tool have the same expectation on the order of symbols. [1] https://lore.kernel.org/live-patching/20230615170048.2382735-1-song@kernel.org/T/#u Fixes: 6eb4bd92c1ce ("kallsyms: strip LTO suffixes from static functions") Reported-by: Song Liu <song@kernel.org> Signed-off-by: Yonghong Song <yhs@fb.com> Reviewed-by: Zhen Lei <thunder.leizhen@huawei.com> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com> Acked-by: Song Liu <song@kernel.org> Link: https://lore.kernel.org/r/20230628181926.4102448-1-yhs@fb.com Signed-off-by: Kees Cook <keescook@chromium.org>
-rw-r--r--kernel/kallsyms.c5
-rw-r--r--scripts/kallsyms.c6
2 files changed, 5 insertions, 6 deletions
diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index 7982cc9d497c..016d997131d4 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -174,11 +174,10 @@ static bool cleanup_symbol_name(char *s)
* 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:
+ * character in an identifier in C. Suffixes only in LLVM LTO observed:
* - foo.llvm.[0-9a-f]+
- * - foo.[0-9a-f]+
*/
- res = strchr(s, '.');
+ res = strstr(s, ".llvm.");
if (res) {
*res = '\0';
return true;
diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c
index d387c9381650..16c87938b316 100644
--- a/scripts/kallsyms.c
+++ b/scripts/kallsyms.c
@@ -349,10 +349,10 @@ static void cleanup_symbol_name(char *s)
* ASCII[_] = 5f
* ASCII[a-z] = 61,7a
*
- * As above, replacing '.' with '\0' does not affect the main sorting,
- * but it helps us with subsorting.
+ * As above, replacing the first '.' in ".llvm." with '\0' does not
+ * affect the main sorting, but it helps us with subsorting.
*/
- p = strchr(s, '.');
+ p = strstr(s, ".llvm.");
if (p)
*p = '\0';
}