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Date: Tue, 18 Jul 2017 15:33:28 -0700
From: Thomas Garnier <thgarnie@...gle.com>
To: Herbert Xu <herbert@...dor.apana.org.au>,
"David S . Miller" <davem@...emloft.net>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>,
"H . Peter Anvin" <hpa@...or.com>,
Peter Zijlstra <peterz@...radead.org>,
Josh Poimboeuf <jpoimboe@...hat.com>,
Thomas Garnier <thgarnie@...gle.com>,
Arnd Bergmann <arnd@...db.de>,
Matthias Kaehlcke <mka@...omium.org>,
Boris Ostrovsky <boris.ostrovsky@...cle.com>,
Juergen Gross <jgross@...e.com>,
Paolo Bonzini <pbonzini@...hat.com>,
Radim Krčmář <rkrcmar@...hat.com>,
Joerg Roedel <joro@...tes.org>,
Andy Lutomirski <luto@...nel.org>,
Borislav Petkov <bp@...en8.de>,
"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
Brian Gerst <brgerst@...il.com>,
Borislav Petkov <bp@...e.de>,
Christian Borntraeger <borntraeger@...ibm.com>,
"Rafael J . Wysocki" <rjw@...ysocki.net>,
Len Brown <len.brown@...el.com>,
Pavel Machek <pavel@....cz>,
Tejun Heo <tj@...nel.org>,
Christoph Lameter <cl@...ux.com>,
Kees Cook <keescook@...omium.org>,
Paul Gortmaker <paul.gortmaker@...driver.com>,
Chris Metcalf <cmetcalf@...lanox.com>,
"Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Christopher Li <sparse@...isli.org>,
Dou Liyang <douly.fnst@...fujitsu.com>,
Masahiro Yamada <yamada.masahiro@...ionext.com>,
Daniel Borkmann <daniel@...earbox.net>,
Markus Trippelsdorf <markus@...ppelsdorf.de>,
Peter Foley <pefoley2@...oley.com>,
Steven Rostedt <rostedt@...dmis.org>,
Tim Chen <tim.c.chen@...ux.intel.com>,
Ard Biesheuvel <ard.biesheuvel@...aro.org>,
Catalin Marinas <catalin.marinas@....com>,
Matthew Wilcox <mawilcox@...rosoft.com>,
Michal Hocko <mhocko@...e.com>,
Rob Landley <rob@...dley.net>,
Jiri Kosina <jkosina@...e.cz>,
"H . J . Lu" <hjl.tools@...il.com>,
Paul Bolle <pebolle@...cali.nl>,
Baoquan He <bhe@...hat.com>,
Daniel Micay <danielmicay@...il.com>
Cc: x86@...nel.org,
linux-crypto@...r.kernel.org,
linux-kernel@...r.kernel.org,
xen-devel@...ts.xenproject.org,
kvm@...r.kernel.org,
linux-pm@...r.kernel.org,
linux-arch@...r.kernel.org,
linux-sparse@...r.kernel.org,
kernel-hardening@...ts.openwall.com
Subject: [RFC 17/22] compiler: Option to default to hidden symbols
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.
Signed-off-by: Thomas Garnier <thgarnie@...gle.com>
---
arch/x86/boot/boot.h | 2 +-
arch/x86/include/asm/setup.h | 2 +-
include/asm-generic/sections.h | 6 ++++++
include/linux/compiler.h | 8 ++++++++
init/Kconfig | 7 +++++++
kernel/kallsyms.c | 16 ++++++++--------
6 files changed, 31 insertions(+), 10 deletions(-)
diff --git a/arch/x86/boot/boot.h b/arch/x86/boot/boot.h
index ef5a9cc66fb8..d726c35bdd96 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 e4585a393965..f3ffad82bdc0 100644
--- a/arch/x86/include/asm/setup.h
+++ b/arch/x86/include/asm/setup.h
@@ -66,7 +66,7 @@ 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/include/asm-generic/sections.h b/include/asm-generic/sections.h
index 532372c6cf15..27c12f6dd6e2 100644
--- a/include/asm-generic/sections.h
+++ b/include/asm-generic/sections.h
@@ -28,6 +28,9 @@
* __entry_text_start, __entry_text_end
* __ctors_start, __ctors_end
*/
+#ifdef CONFIG_DEFAULT_HIDDEN
+#pragma GCC visibility push(default)
+#endif
extern char _text[], _stext[], _etext[];
extern char _data[], _sdata[], _edata[];
extern char __bss_start[], __bss_stop[];
@@ -42,6 +45,9 @@ extern char __start_rodata[], __end_rodata[];
/* Start and end of .ctors section - used for constructor calls. */
extern char __ctors_start[], __ctors_end[];
+#ifdef CONFIG_DEFAULT_HIDDEN
+#pragma GCC visibility pop
+#endif
extern __visible const void __nosave_begin, __nosave_end;
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index eca8ad75e28b..876b827fe4a7 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -78,6 +78,14 @@ extern void __chk_io_ptr(const volatile void __iomem *);
#include <linux/compiler-clang.h>
#endif
+/* Useful for Position Independent Code to reduce global references */
+#ifdef CONFIG_DEFAULT_HIDDEN
+#pragma GCC visibility push(hidden)
+#define __default_visibility __attribute__((visibility ("default")))
+#else
+#define __default_visibility
+#endif
+
/*
* Generic compiler-dependent macros required for kernel
* build go below this comment. Actual compiler/compiler version
diff --git a/init/Kconfig b/init/Kconfig
index 4fb5d6fc2c4f..a93626d40355 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1635,6 +1635,13 @@ config PROFILING
config TRACEPOINTS
bool
+#
+# Default to hidden visibility for all symbols.
+# Useful for Position Independent Code to reduce global references.
+#
+config DEFAULT_HIDDEN
+ bool
+
source "arch/Kconfig"
endmenu # General setup
diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index 127e7cfafa55..252019c8c3a9 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -32,24 +32,24 @@
* 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 long 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 long kallsyms_markers[] __weak;
+extern const unsigned long kallsyms_markers[] __weak __default_visibility;
static inline int is_kernel_inittext(unsigned long addr)
{
--
2.13.2.932.g7449e964c-goog
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