[PATCH v2] kasan: account for destructor sections

[PATCH v2] kasan: account for destructor sections

[Dmitry Vyukov]

If CONFIG_KASAN is enabled and gcc is configured with
--disable-initfini-array, gcc emits .ctors/.dtors and
.text.startup/.text.exit sections instead of
.init_array/.fini_array.
.dtors section is not explicitly accounted in the linker
script and messes vvar/percpu layout. Want:

ffffffff822bfd80 D _edata
ffffffff822c0000 D __vvar_beginning_hack
ffffffff822c0000 A __vvar_page
ffffffff822c0080 0000000000000098 D vsyscall_gtod_data
ffffffff822c1000 A __init_begin
ffffffff822c1000 D init_per_cpu__irq_stack_union
ffffffff822c1000 A __per_cpu_load
ffffffff822d3000 D init_per_cpu__gdt_page

Got:

ffffffff8279a600 D _edata
ffffffff8279b000 A __vvar_page
ffffffff8279c000 A __init_begin
ffffffff8279c000 D init_per_cpu__irq_stack_union
ffffffff8279c000 A __per_cpu_load
ffffffff8279e000 D __vvar_beginning_hack
ffffffff8279e080 0000000000000098 D vsyscall_gtod_data
ffffffff827ae000 D init_per_cpu__gdt_page

This happens because __vvar_page and .vvar get different
addresses in arch/x86/kernel/vmlinux.lds.S:

	. = ALIGN(PAGE_SIZE);
	__vvar_page = .;

	.vvar : AT(ADDR(.vvar) - LOAD_OFFSET) {
		/* work around gold bug 13023 */
		__vvar_beginning_hack = .;

Discard .dtors/.fini_array/.text.exit, since we don't call dtors.
Merge .text.startup into init text.

Signed-off-by: Dmitry Vyukov <dvyukov@google.com>

---

Changes since v1:
 - discard .dtors
 - don't define .mem sections
---
 include/asm-generic/vmlinux.lds.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 6a67ab9..081d0f2 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -542,15 +542,19 @@
 
 #define INIT_TEXT							\
 	*(.init.text)							\
+	*(.text.startup)						\
 	MEM_DISCARD(init.text)
 
 #define EXIT_DATA							\
 	*(.exit.data)							\
+	*(.fini_array)							\
+	*(.dtors)							\
 	MEM_DISCARD(exit.data)						\
 	MEM_DISCARD(exit.rodata)
 
 #define EXIT_TEXT							\
 	*(.exit.text)							\
+	*(.text.exit)							\
 	MEM_DISCARD(exit.text)
 
 #define EXIT_CALL							\
-- 
2.8.0.rc3.226.g39d4020

Re: [PATCH v2] kasan: account for destructor sections

[Andrey Ryabinin]

2016-06-23 19:06 GMT+03:00 Dmitry Vyukov <dvyukov@google.com>:

Subsystem prefix in subject is wrong. Change it to vmlinux.lds

> If CONFIG_KASAN is enabled and gcc is configured with
> --disable-initfini-array, gcc emits .ctors/.dtors and
> .text.startup/.text.exit sections instead of
> .init_array/.fini_array.
> .dtors section is not explicitly accounted in the linker
> script and messes vvar/percpu layout. Want:

As far as I found out this happens if gold linker has been used.
Gcc configuration is irrelevant here.


> ffffffff822bfd80 D _edata
> ffffffff822c0000 D __vvar_beginning_hack
> ffffffff822c0000 A __vvar_page
> ffffffff822c0080 0000000000000098 D vsyscall_gtod_data
> ffffffff822c1000 A __init_begin
> ffffffff822c1000 D init_per_cpu__irq_stack_union
> ffffffff822c1000 A __per_cpu_load
> ffffffff822d3000 D init_per_cpu__gdt_page
>
> Got:
>
> ffffffff8279a600 D _edata
> ffffffff8279b000 A __vvar_page
> ffffffff8279c000 A __init_begin
> ffffffff8279c000 D init_per_cpu__irq_stack_union
> ffffffff8279c000 A __per_cpu_load
> ffffffff8279e000 D __vvar_beginning_hack
> ffffffff8279e080 0000000000000098 D vsyscall_gtod_data
> ffffffff827ae000 D init_per_cpu__gdt_page
>
> This happens because __vvar_page and .vvar get different
> addresses in arch/x86/kernel/vmlinux.lds.S:
>
>         . = ALIGN(PAGE_SIZE);
>         __vvar_page = .;
>
>         .vvar : AT(ADDR(.vvar) - LOAD_OFFSET) {
>                 /* work around gold bug 13023 */
>                 __vvar_beginning_hack = .;
>
> Discard .dtors/.fini_array/.text.exit, since we don't call dtors.
> Merge .text.startup into init text.
>
> Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
>
> ---
>
> Changes since v1:
>  - discard .dtors
>  - don't define .mem sections
> ---
>  include/asm-generic/vmlinux.lds.h | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> index 6a67ab9..081d0f2 100644
> --- a/include/asm-generic/vmlinux.lds.h
> +++ b/include/asm-generic/vmlinux.lds.h
> @@ -542,15 +542,19 @@
>
>  #define INIT_TEXT                                                      \
>         *(.init.text)                                                   \
> +       *(.text.startup)                                                \
>         MEM_DISCARD(init.text)
>
>  #define EXIT_DATA                                                      \
>         *(.exit.data)                                                   \
> +       *(.fini_array)                                                  \
> +       *(.dtors)                                                       \
>         MEM_DISCARD(exit.data)                                          \
>         MEM_DISCARD(exit.rodata)
>
>  #define EXIT_TEXT                                                      \
>         *(.exit.text)                                                   \
> +       *(.text.exit)                                                   \
>         MEM_DISCARD(exit.text)
>
>  #define EXIT_CALL                                                      \
> --
> 2.8.0.rc3.226.g39d4020
>