From mboxrd@z Thu Jan 1 00:00:00 1970 From: Thomas Garnier Subject: [PATCH v6 15/27] compiler: Option to default to hidden symbols Date: Thu, 31 Jan 2019 11:24:22 -0800 Message-Id: <20190131192533.34130-16-thgarnie@chromium.org> In-Reply-To: <20190131192533.34130-1-thgarnie@chromium.org> References: <20190131192533.34130-1-thgarnie@chromium.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit To: kernel-hardening@lists.openwall.com Cc: kristen@linux.intel.com, Thomas Garnier , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , x86@kernel.org, Luis Chamberlain , Greg Kroah-Hartman , "Rafael J. Wysocki" , Arnd Bergmann , Luc Van Oostenryck , Steven Rostedt , Jason Baron , Thomas Garnier , Jordan Borgner , Masami Hiramatsu , Masahiro Yamada , "Peter Zijlstra (Intel)" , Andrew Morton , Kees Cook , Mathieu Desnoyers , Arnaldo Carvalho de Melo , Andi Kleen , Jan Beulich , Song Liu , Adrian Hunter , Alexander Shishkin , linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, linux-sparse@vger.kernel.org List-ID: Provide an option to default visibility to hidden except for key symbols. This option is disabled by default and will be used by x86_64 PIE support to remove errors between compilation units. The default visibility is also enabled for external symbols that are compared as they maybe equals (start/end of sections). In this case, older versions of GCC will remove the comparison if the symbols are hidden. This issue exists at least on gcc 4.9 and before. Signed-off-by: Thomas Garnier --- arch/x86/boot/boot.h | 2 +- arch/x86/include/asm/setup.h | 2 +- arch/x86/kernel/cpu/microcode/core.c | 4 ++-- drivers/base/firmware_loader/main.c | 4 ++-- include/asm-generic/sections.h | 6 ++++++ include/linux/compiler.h | 7 +++++++ init/Kconfig | 7 +++++++ kernel/kallsyms.c | 16 ++++++++-------- kernel/trace/trace.h | 4 ++-- lib/dynamic_debug.c | 4 ++-- 10 files changed, 38 insertions(+), 18 deletions(-) diff --git a/arch/x86/boot/boot.h b/arch/x86/boot/boot.h index 32a09eb5c101..c4afcfecc817 100644 --- a/arch/x86/boot/boot.h +++ b/arch/x86/boot/boot.h @@ -193,7 +193,7 @@ static inline bool memcmp_gs(const void *s1, addr_t s2, size_t len) } /* Heap -- available for dynamic lists. */ -extern char _end[]; +extern char _end[] __default_visibility; extern char *HEAP; extern char *heap_end; #define RESET_HEAP() ((void *)( HEAP = _end )) diff --git a/arch/x86/include/asm/setup.h b/arch/x86/include/asm/setup.h index ed8ec011a9fd..74f0a8d87986 100644 --- a/arch/x86/include/asm/setup.h +++ b/arch/x86/include/asm/setup.h @@ -71,7 +71,7 @@ static inline void x86_ce4100_early_setup(void) { } * This is set up by the setup-routine at boot-time */ extern struct boot_params boot_params; -extern char _text[]; +extern char _text[] __default_visibility; static inline bool kaslr_enabled(void) { diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c index 97f9ada9ceda..04ca89e65f79 100644 --- a/arch/x86/kernel/cpu/microcode/core.c +++ b/arch/x86/kernel/cpu/microcode/core.c @@ -149,8 +149,8 @@ static bool __init check_loader_disabled_bsp(void) return *res; } -extern struct builtin_fw __start_builtin_fw[]; -extern struct builtin_fw __end_builtin_fw[]; +extern struct builtin_fw __start_builtin_fw[] __default_visibility; +extern struct builtin_fw __end_builtin_fw[] __default_visibility; bool get_builtin_firmware(struct cpio_data *cd, const char *name) { diff --git a/drivers/base/firmware_loader/main.c b/drivers/base/firmware_loader/main.c index 8e9213b36e31..f04096161a52 100644 --- a/drivers/base/firmware_loader/main.c +++ b/drivers/base/firmware_loader/main.c @@ -94,8 +94,8 @@ static struct firmware_cache fw_cache; #ifdef CONFIG_FW_LOADER -extern struct builtin_fw __start_builtin_fw[]; -extern struct builtin_fw __end_builtin_fw[]; +extern struct builtin_fw __start_builtin_fw[] __default_visibility; +extern struct builtin_fw __end_builtin_fw[] __default_visibility; static void fw_copy_to_prealloc_buf(struct firmware *fw, void *buf, size_t size) diff --git a/include/asm-generic/sections.h b/include/asm-generic/sections.h index d79abca81a52..94f072f3a48d 100644 --- a/include/asm-generic/sections.h +++ b/include/asm-generic/sections.h @@ -32,6 +32,9 @@ * __softirqentry_text_start, __softirqentry_text_end * __start_opd, __end_opd */ +#ifdef CONFIG_DEFAULT_HIDDEN_SYMS +#pragma GCC visibility push(default) +#endif extern char _text[], _stext[], _etext[]; extern char _data[], _sdata[], _edata[]; extern char __bss_start[], __bss_stop[]; @@ -49,6 +52,9 @@ extern char __start_once[], __end_once[]; /* Start and end of .ctors section - used for constructor calls. */ extern char __ctors_start[], __ctors_end[]; +#ifdef CONFIG_DEFAULT_HIDDEN_SYMS +#pragma GCC visibility pop +#endif /* Start and end of .opd section - used for function descriptors. */ extern char __start_opd[], __end_opd[]; diff --git a/include/linux/compiler.h b/include/linux/compiler.h index 87692fdae97a..5c0723604a52 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -287,6 +287,13 @@ unsigned long read_word_at_a_time(const void *addr) __u.__val; \ }) +#ifdef CONFIG_DEFAULT_HIDDEN_SYMS +#pragma GCC visibility push(hidden) +#define __default_visibility __attribute__((visibility ("default"))) +#else +#define __default_visibility +#endif + #endif /* __KERNEL__ */ /* diff --git a/init/Kconfig b/init/Kconfig index bb383615823a..116e0de4817f 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -1848,6 +1848,13 @@ config CMDLINE_OVERRIDE endif +# +# Default to hidden visibility for all symbols. +# Useful for Position Independent Code to reduce global references. +# +config DEFAULT_HIDDEN_SYMS + bool + endmenu # General setup source "arch/Kconfig" diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c index 14934afa9e68..547affc40b68 100644 --- a/kernel/kallsyms.c +++ b/kernel/kallsyms.c @@ -29,24 +29,24 @@ * These will be re-linked against their real values * during the second link stage. */ -extern const unsigned long kallsyms_addresses[] __weak; -extern const int kallsyms_offsets[] __weak; -extern const u8 kallsyms_names[] __weak; +extern const unsigned long kallsyms_addresses[] __weak __default_visibility; +extern const int kallsyms_offsets[] __weak __default_visibility; +extern const u8 kallsyms_names[] __weak __default_visibility; /* * Tell the compiler that the count isn't in the small data section if the arch * has one (eg: FRV). */ extern const unsigned int kallsyms_num_syms -__attribute__((weak, section(".rodata"))); +__attribute__((weak, section(".rodata"))) __default_visibility; extern const unsigned long kallsyms_relative_base -__attribute__((weak, section(".rodata"))); +__attribute__((weak, section(".rodata"))) __default_visibility; -extern const u8 kallsyms_token_table[] __weak; -extern const u16 kallsyms_token_index[] __weak; +extern const u8 kallsyms_token_table[] __weak __default_visibility; +extern const u16 kallsyms_token_index[] __weak __default_visibility; -extern const unsigned int kallsyms_markers[] __weak; +extern const unsigned int kallsyms_markers[] __weak __default_visibility; /* * Expand a compressed symbol data into the resulting uncompressed string, diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h index 08900828d282..5246977a2db7 100644 --- a/kernel/trace/trace.h +++ b/kernel/trace/trace.h @@ -1809,8 +1809,8 @@ extern int trace_event_enable_disable(struct trace_event_file *file, int enable, int soft_disable); extern int tracing_alloc_snapshot(void); -extern const char *__start___trace_bprintk_fmt[]; -extern const char *__stop___trace_bprintk_fmt[]; +extern const char *__start___trace_bprintk_fmt[] __default_visibility; +extern const char *__stop___trace_bprintk_fmt[] __default_visibility; extern const char *__start___tracepoint_str[]; extern const char *__stop___tracepoint_str[]; diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c index dbf2b457e47e..05482e65ae7d 100644 --- a/lib/dynamic_debug.c +++ b/lib/dynamic_debug.c @@ -37,8 +37,8 @@ #include #include -extern struct _ddebug __start___verbose[]; -extern struct _ddebug __stop___verbose[]; +extern struct _ddebug __start___verbose[] __default_visibility; +extern struct _ddebug __stop___verbose[] __default_visibility; struct ddebug_table { struct list_head link; -- 2.20.1.495.gaa96b0ce6b-goog