From: Yonghong Song yhs@fb.com
[ Upstream commit 8cc32a9bbf2934d90762d9de0187adcb5ad46a11 ]
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.o...
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 Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/kallsyms.c | 5 ++--- scripts/kallsyms.c | 6 +++--- 2 files changed, 5 insertions(+), 6 deletions(-)
diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c index 77747391f49b6..4874508bb950e 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 0d2db41177b23..13af6d0ff845d 100644 --- a/scripts/kallsyms.c +++ b/scripts/kallsyms.c @@ -346,10 +346,10 @@ 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'; }