[PATCH v4 00/27] x86: PIE support and option to extend KASLR randomization

[PATCH v4 00/27] x86: PIE support and option to extend KASLR randomization

[Thomas Garnier via Virtualization]

Changes:
 - patch v4:
   - Simplify early boot by removing global variables.
   - Modify the mcount location script for __mcount_loc intead of the address
     read in the ftrace implementation.
   - Edit commit description to explain better where the kernel can be located.
   - Streamlined the testing done on each patch proposal. Always testing
     hibernation, suspend, ftrace and kprobe to ensure no regressions.
 - patch v3:
   - Update on message to describe longer term PIE goal.
   - Minor change on ftrace if condition.
   - Changed code using xchgq.
 - patch v2:
   - Adapt patch to work post KPTI and compiler changes
   - Redo all performance testing with latest configs and compilers
   - Simplify mov macro on PIE (MOVABS now)
   - Reduce GOT footprint
 - patch v1:
   - Simplify ftrace implementation.
   - Use gcc mstack-protector-guard-reg=%gs with PIE when possible.
 - rfc v3:
   - Use --emit-relocs instead of -pie to reduce dynamic relocation space on
     mapped memory. It also simplifies the relocation process.
   - Move the start the module section next to the kernel. Remove the need for
     -mcmodel=large on modules. Extends module space from 1 to 2G maximum.
   - Support for XEN PVH as 32-bit relocations can be ignored with
     --emit-relocs.
   - Support for GOT relocations previously done automatically with -pie.
   - Remove need for dynamic PLT in modules.
   - Support dymamic GOT for modules.
 - rfc v2:
   - Add support for global stack cookie while compiler default to fs without
     mcmodel=kernel
   - Change patch 7 to correctly jump out of the identity mapping on kexec load
     preserve.

These patches make the changes necessary to build the kernel as Position
Independent Executable (PIE) on x86_64. A PIE kernel can be relocated below
the top 2G of the virtual address space. It allows to optionally extend the
KASLR randomization range from 1G to 3G. The chosen range is the one currently
available, future changes will allow the kernel module to have a wider
randomization range.

Thanks a lot to Ard Biesheuvel & Kees Cook on their feedback on compiler
changes, PIE support and KASLR in general. Thanks to Roland McGrath on his
feedback for using -pie versus --emit-relocs and details on compiler code
generation.

The patches:
 - 1-3, 5-13, 18-19: Change in assembly code to be PIE compliant.
 - 4: Add a new _ASM_MOVABS macro to fetch a symbol address generically.
 - 14: Adapt percpu design to work correctly when PIE is enabled.
 - 15: Provide an option to default visibility to hidden except for key symbols.
       It removes errors between compilation units.
 - 16: Add PROVIDE_HIDDEN replacement on the linker script for weak symbols to
       reduce GOT footprint.
 - 17: Adapt relocation tool to handle PIE binary correctly.
 - 20: Add support for global cookie.
 - 21: Support ftrace with PIE (used on Ubuntu config).
 - 22: Add option to move the module section just after the kernel.
 - 23: Adapt module loading to support PIE with dynamic GOT.
 - 24: Make the GOT read-only.
 - 25: Add the CONFIG_X86_PIE option (off by default).
 - 26: Adapt relocation tool to generate a 64-bit relocation table.
 - 27: Add the CONFIG_RANDOMIZE_BASE_LARGE option to increase relocation range
       from 1G to 3G (off by default).

Performance/Size impact:

Size of vmlinux (Default configuration):
 File size:
 - PIE disabled: +0.18%
 - PIE enabled: -1.977% (less relocations)
 .text section:
 - PIE disabled: same
 - PIE enabled: same

Size of vmlinux (Ubuntu configuration):
 File size:
 - PIE disabled: +0.21%
 - PIE enabled: +10%
 .text section:
 - PIE disabled: same
 - PIE enabled: +0.001%

The size increase is mainly due to not having access to the 32-bit signed
relocation that can be used with mcmodel=kernel. A small part is due to reduced
optimization for PIE code. This bug [1] was opened with gcc to provide a better
code generation for kernel PIE.

Hackbench (50% and 1600% on thread/process for pipe/sockets):
 - PIE disabled: no significant change (avg -/+ 0.5% on latest test).
 - PIE enabled: between -1% to +1% in average (default and Ubuntu config).

Kernbench (average of 10 Half and Optimal runs):
 Elapsed Time:
 - PIE disabled: no significant change (avg -0.5%)
 - PIE enabled: average -0.5% to +0.5%
 System Time:
 - PIE disabled: no significant change (avg -0.1%)
 - PIE enabled: average -0.4% to +0.4%.

[1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82303

diffstat:
 Documentation/x86/x86_64/mm.txt              |    3 
 arch/x86/Kconfig                             |   45 ++++++
 arch/x86/Makefile                            |   58 ++++++++
 arch/x86/boot/boot.h                         |    2 
 arch/x86/boot/compressed/Makefile            |    5 
 arch/x86/boot/compressed/misc.c              |   10 +
 arch/x86/crypto/aes-x86_64-asm_64.S          |   45 ++++--
 arch/x86/crypto/aesni-intel_asm.S            |    8 -
 arch/x86/crypto/aesni-intel_avx-x86_64.S     |    6 
 arch/x86/crypto/camellia-aesni-avx-asm_64.S  |   42 +++---
 arch/x86/crypto/camellia-aesni-avx2-asm_64.S |   44 +++---
 arch/x86/crypto/camellia-x86_64-asm_64.S     |    8 -
 arch/x86/crypto/cast5-avx-x86_64-asm_64.S    |   50 ++++---
 arch/x86/crypto/cast6-avx-x86_64-asm_64.S    |   44 +++---
 arch/x86/crypto/des3_ede-asm_64.S            |   96 +++++++++-----
 arch/x86/crypto/ghash-clmulni-intel_asm.S    |    4 
 arch/x86/crypto/glue_helper-asm-avx.S        |    4 
 arch/x86/crypto/glue_helper-asm-avx2.S       |    6 
 arch/x86/crypto/sha256-avx2-asm.S            |   23 ++-
 arch/x86/entry/calling.h                     |    2 
 arch/x86/entry/entry_32.S                    |    3 
 arch/x86/entry/entry_64.S                    |   25 ++-
 arch/x86/include/asm/asm.h                   |    1 
 arch/x86/include/asm/bug.h                   |    2 
 arch/x86/include/asm/ftrace.h                |    4 
 arch/x86/include/asm/jump_label.h            |    8 -
 arch/x86/include/asm/kvm_host.h              |    8 -
 arch/x86/include/asm/module.h                |   11 +
 arch/x86/include/asm/page_64_types.h         |    9 +
 arch/x86/include/asm/paravirt_types.h        |   12 +
 arch/x86/include/asm/percpu.h                |   25 ++-
 arch/x86/include/asm/pgtable_64_types.h      |    6 
 arch/x86/include/asm/pm-trace.h              |    2 
 arch/x86/include/asm/processor.h             |   16 +-
 arch/x86/include/asm/sections.h              |    8 +
 arch/x86/include/asm/setup.h                 |    2 
 arch/x86/include/asm/stackprotector.h        |   19 ++
 arch/x86/kernel/Makefile                     |    6 
 arch/x86/kernel/acpi/wakeup_64.S             |   31 ++--
 arch/x86/kernel/asm-offsets.c                |    3 
 arch/x86/kernel/asm-offsets_32.c             |    3 
 arch/x86/kernel/asm-offsets_64.c             |    3 
 arch/x86/kernel/cpu/common.c                 |    3 
 arch/x86/kernel/cpu/microcode/core.c         |    4 
 arch/x86/kernel/ftrace.c                     |   42 +++++-
 arch/x86/kernel/head64.c                     |   23 ++-
 arch/x86/kernel/head_32.S                    |    3 
 arch/x86/kernel/head_64.S                    |   31 +++-
 arch/x86/kernel/kvm.c                        |    6 
 arch/x86/kernel/module.c                     |  181 ++++++++++++++++++++++++++-
 arch/x86/kernel/module.lds                   |    3 
 arch/x86/kernel/process.c                    |    5 
 arch/x86/kernel/relocate_kernel_64.S         |   16 +-
 arch/x86/kernel/setup_percpu.c               |    5 
 arch/x86/kernel/vmlinux.lds.S                |   13 +
 arch/x86/kvm/svm.c                           |    4 
 arch/x86/lib/cmpxchg16b_emu.S                |    8 -
 arch/x86/mm/dump_pagetables.c                |    3 
 arch/x86/power/hibernate_asm_64.S            |    4 
 arch/x86/tools/relocs.c                      |  169 +++++++++++++++++++++++--
 arch/x86/tools/relocs.h                      |    4 
 arch/x86/tools/relocs_common.c               |   15 +-
 arch/x86/xen/xen-asm.S                       |   12 -
 arch/x86/xen/xen-head.S                      |   11 -
 arch/x86/xen/xen-pvh.S                       |   13 +
 drivers/base/firmware_loader/main.c          |    4 
 include/asm-generic/sections.h               |    6 
 include/asm-generic/vmlinux.lds.h            |   12 +
 include/linux/compiler.h                     |    7 +
 init/Kconfig                                 |   16 ++
 kernel/kallsyms.c                            |   16 +-
 kernel/trace/trace.h                         |    4 
 lib/dynamic_debug.c                          |    4 
 scripts/link-vmlinux.sh                      |   14 ++
 scripts/recordmcount.c                       |   79 +++++++----
 75 files changed, 1109 insertions(+), 343 deletions(-)

[PATCH v4 15/27] compiler: Option to default to hidden symbols

[Thomas Garnier]

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 <thgarnie@google.com>
---
 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 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 ae13bc974416..083a6e99b884 100644
--- a/arch/x86/include/asm/setup.h
+++ b/arch/x86/include/asm/setup.h
@@ -68,7 +68,7 @@ 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 77e201301528..6a4f5d9d7eb6 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 0943e7065e0e..2ffd019af2d4 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 849cd8eb5ca0..0a0e23405ddd 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
+#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
+#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 ab4711c63601..a9ac84e37af9 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -278,6 +278,13 @@ unsigned long read_word_at_a_time(const void *addr)
 	__u.__val;					\
 })
 
+#ifdef CONFIG_DEFAULT_HIDDEN
+#pragma GCC visibility push(hidden)
+#define __default_visibility  __attribute__((visibility ("default")))
+#else
+#define __default_visibility
+#endif
+
 #endif /* __KERNEL__ */
 
 #endif /* __ASSEMBLY__ */
diff --git a/init/Kconfig b/init/Kconfig
index e4acab9f9fd1..f16247675f84 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1694,6 +1694,13 @@ 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 a23e21ada81b..f4e58b7a6daf 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 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;
 
 /*
  * Expand a compressed symbol data into the resulting uncompressed string,
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 6fb46a06c9dc..e659f452cf8c 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -1746,8 +1746,8 @@ 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 c7c96bc7654a..40b752b53627 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -37,8 +37,8 @@
 #include <linux/device.h>
 #include <linux/netdevice.h>
 
-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;
-- 
2.17.0.921.gf22659ad46-goog

[PATCH v4 15/27] compiler: Option to default to hidden symbols

[Thomas Garnier]

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 <thgarnie@google.com>
---
 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 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 ae13bc974416..083a6e99b884 100644
--- a/arch/x86/include/asm/setup.h
+++ b/arch/x86/include/asm/setup.h
@@ -68,7 +68,7 @@ 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 77e201301528..6a4f5d9d7eb6 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 0943e7065e0e..2ffd019af2d4 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 849cd8eb5ca0..0a0e23405ddd 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
+#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
+#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 ab4711c63601..a9ac84e37af9 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -278,6 +278,13 @@ unsigned long read_word_at_a_time(const void *addr)
 	__u.__val;					\
 })
 
+#ifdef CONFIG_DEFAULT_HIDDEN
+#pragma GCC visibility push(hidden)
+#define __default_visibility  __attribute__((visibility ("default")))
+#else
+#define __default_visibility
+#endif
+
 #endif /* __KERNEL__ */
 
 #endif /* __ASSEMBLY__ */
diff --git a/init/Kconfig b/init/Kconfig
index e4acab9f9fd1..f16247675f84 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1694,6 +1694,13 @@ 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 a23e21ada81b..f4e58b7a6daf 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 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;
 
 /*
  * Expand a compressed symbol data into the resulting uncompressed string,
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 6fb46a06c9dc..e659f452cf8c 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -1746,8 +1746,8 @@ 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 c7c96bc7654a..40b752b53627 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -37,8 +37,8 @@
 #include <linux/device.h>
 #include <linux/netdevice.h>
 
-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;
-- 
2.17.0.921.gf22659ad46-goog

[PATCH v4 24/27] x86/mm: Make the x86 GOT read-only

[Thomas Garnier]

The GOT is changed during early boot when relocations are applied. Make
it read-only directly. This table exists only for PIE binary.

Position Independent Executable (PIE) support will allow to extend the
KASLR randomization range 0xffffffff80000000.

Signed-off-by: Thomas Garnier <thgarnie@google.com>
---
 include/asm-generic/vmlinux.lds.h | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index e373e2e10f6a..e5b0710fe693 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -314,6 +314,17 @@
 	__end_ro_after_init = .;
 #endif
 
+#ifdef CONFIG_X86_PIE
+#define RO_GOT_X86							\
+	.got        : AT(ADDR(.got) - LOAD_OFFSET) {			\
+		VMLINUX_SYMBOL(__start_got) = .;			\
+		*(.got);						\
+		VMLINUX_SYMBOL(__end_got) = .;				\
+	}
+#else
+#define RO_GOT_X86
+#endif
+
 /*
  * Read only Data
  */
@@ -370,6 +381,7 @@
 		__end_builtin_fw = .;					\
 	}								\
 									\
+	RO_GOT_X86							\
 	TRACEDATA							\
 									\
 	/* Kernel symbol table: Normal symbols */			\
-- 
2.17.0.921.gf22659ad46-goog

[PATCH v4 24/27] x86/mm: Make the x86 GOT read-only

[Thomas Garnier]

The GOT is changed during early boot when relocations are applied. Make
it read-only directly. This table exists only for PIE binary.

Position Independent Executable (PIE) support will allow to extend the
KASLR randomization range 0xffffffff80000000.

Signed-off-by: Thomas Garnier <thgarnie@google.com>
---
 include/asm-generic/vmlinux.lds.h | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index e373e2e10f6a..e5b0710fe693 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -314,6 +314,17 @@
 	__end_ro_after_init = .;
 #endif
 
+#ifdef CONFIG_X86_PIE
+#define RO_GOT_X86							\
+	.got        : AT(ADDR(.got) - LOAD_OFFSET) {			\
+		VMLINUX_SYMBOL(__start_got) = .;			\
+		*(.got);						\
+		VMLINUX_SYMBOL(__end_got) = .;				\
+	}
+#else
+#define RO_GOT_X86
+#endif
+
 /*
  * Read only Data
  */
@@ -370,6 +381,7 @@
 		__end_builtin_fw = .;					\
 	}								\
 									\
+	RO_GOT_X86							\
 	TRACEDATA							\
 									\
 	/* Kernel symbol table: Normal symbols */			\
-- 
2.17.0.921.gf22659ad46-goog