Messages in this thread Patch in this message | | | Date | Mon, 28 Jun 2021 14:19:52 -0700 | From | Nathan Chancellor <> | Subject | Re: [PATCH v3] kallsyms: strip LTO suffixes from static functions |
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On Mon, Jun 28, 2021 at 01:31:06PM -0700, Nick Desaulniers wrote: > 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. > > LLVM has yet another name mangling scheme used by thin LTO. Strip off > these suffixes so that we can continue to hook such static functions. > > Reported-by: KE.LI(Lieke) <like1@oppo.com> > Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> > --- > Changes v2 -> V3: > * Un-nest preprocessor checks, as per Nathan. > > Changes v1 -> v2: > * Both mangling schemes can occur for thinLTO + CFI, this new scheme can > also occur for thinLTO without CFI. Split cleanup_symbol_name() into > two function calls. > * Drop KE.LI's tested by tag. > * Do not carry Fangrui's Reviewed by tag. > * Drop the inline keyword; it is meaningless. > kernel/kallsyms.c | 32 +++++++++++++++++++++++++++++--- > 1 file changed, 29 insertions(+), 3 deletions(-) > > diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c > index 4067564ec59f..143c69e7e75d 100644 > --- a/kernel/kallsyms.c > +++ b/kernel/kallsyms.c > @@ -171,6 +171,26 @@ static unsigned long kallsyms_sym_address(int idx) > return kallsyms_relative_base - 1 - kallsyms_offsets[idx]; > } > > +#ifdef CONFIG_LTO_CLANG_THIN > +/* > + * LLVM appends a suffix for local variables that must be promoted to global > + * scope as part of thin LTO. foo() becomes foo.llvm.974640843467629774. This > + * can break hooking of static functions with kprobes. > + */ > +static bool cleanup_symbol_name_thinlto(char *s) > +{ > + char *res; > + > + res = strstr(s, ".llvm."); > + if (res) > + *res = '\0'; > + > + return res != NULL; > +} > +#else > +static bool cleanup_symbol_name_thinlto(char *s) { return false; } > +#endif /* CONFIG_LTO_CLANG_THIN */ > + > #if defined(CONFIG_CFI_CLANG) && defined(CONFIG_LTO_CLANG_THIN) > /* > * LLVM appends a hash to static function names when ThinLTO and CFI are > @@ -178,7 +198,7 @@ static unsigned long kallsyms_sym_address(int idx) > * 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_thinlto_cfi(char *s) > { > char *res; > > @@ -189,8 +209,14 @@ static inline bool cleanup_symbol_name(char *s) > return res != NULL; > } > #else > -static inline bool cleanup_symbol_name(char *s) { return false; } > -#endif > +static bool cleanup_symbol_name_thinlto_cfi(char *s) { return false; } > +#endif /* CONFIG_CFI_CLANG && CONFIG_LTO_CLANG_THIN */ > + > +static bool cleanup_symbol_name(char *s) > +{ > + return cleanup_symbol_name_thinlto(s) && > + cleanup_symbol_name_thinlto_cfi(s); > +} > > /* Lookup the address for this symbol. Returns 0 if not found. */ > unsigned long kallsyms_lookup_name(const char *name) > -- > 2.32.0.93.g670b81a890-goog >
Is there any reason that we cannot eliminate the stubs and combine the functions, or am I missing something? Completely untested diff.
diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c index c851ca0ed357..014b59ad68a3 100644 --- a/kernel/kallsyms.c +++ b/kernel/kallsyms.c @@ -161,26 +161,36 @@ 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$707af9a22804d33c81801f27dcfe489b. - * This causes confusion and potentially breaks user space tools, so we - * strip the suffix from expanded symbol names. - */ -static inline bool cleanup_symbol_name(char *s) +static inline bool cleanup_symbol_name_thinlto(char *s) { char *res; - res = strrchr(s, '$'); + if (!IS_ENABLED(CONFIG_LTO_CLANG_THIN)) + return false; + + /* + * LLVM appends a suffix for local variables that must be promoted to global + * scope as part of ThinLTO. foo() becomes foo.llvm.974640843467629774. This + * can break hooking of static functions with kprobes. + */ + res = strstr(s, ".llvm."); if (res) *res = '\0'; + /* + * LLVM appends a hash to static function names when ThinLTO and CFI are + * both enabled, i.e. foo() becomes foo$707af9a22804d33c81801f27dcfe489b. + * This causes confusion and potentially breaks user space tools, so we + * strip the suffix from expanded symbol names. + */ + if (IS_ENABLED(CONFIG_CFI_CLANG)) { + res = strrchr(s, '$'); + 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) @@ -195,7 +205,7 @@ 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) + if (cleanup_symbol_name_thinlto(namebuf) && strcmp(namebuf, name) == 0) return kallsyms_sym_address(i); } return module_kallsyms_lookup_name(name);
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