Messages in this thread Patch in this message | | | From | Avi Kivity <> | Subject | [PATCH] Make LIST_POISON less deadly (v2) | Date | Tue, 20 May 2008 10:10:46 +0300 |
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The list macros use LIST_POISON1 and LIST_POISON2 as undereferencable pointers in order to trap erronous use of freed list_heads. Unfortunately userspace can arrange for those pointers to actually be dereferencable, potentially turning an oops to an expolit.
To avoid this allow architectures (currently x86_64 only) to override the default values for these pointers with truly-undereferncable values. This is easy on x86_64 as the virtual address space is smaller than the range spanned by pointer values.
Signed-off-by: Avi Kivity <avi@qumranet.com> ---
Changes since v1: - add CONFIG_ILLEGAL_POINTER_VALUE instead of new header <asm/poison.h>
arch/x86/Kconfig | 5 +++++ include/linux/poison.h | 10 ++++++++-- 2 files changed, 13 insertions(+), 2 deletions(-)
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index fe361ae..54d4e36 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -1021,6 +1021,11 @@ config ARCH_MEMORY_PROBE def_bool X86_64 depends on MEMORY_HOTPLUG +config ILLEGAL_POINTER_VALUE + hex + default 0 if X86_32 + default 0x8888888800000000 if X86_64 + source "mm/Kconfig" config HIGHPTE diff --git a/include/linux/poison.h b/include/linux/poison.h index 9f31683..0d105a5 100644 --- a/include/linux/poison.h +++ b/include/linux/poison.h @@ -1,14 +1,20 @@ #ifndef _LINUX_POISON_H #define _LINUX_POISON_H +#ifdef CONFIG_ILLEGAL_POINTER_VALUE +#define POISON_POINTER_DELTA CONFIG_ILLEGAL_POINTER_VALUE +#else +#define POISON_POINTER_DELTA 0L +#endif + /********** include/linux/list.h **********/ /* * These are non-NULL pointers that will result in page faults * under normal circumstances, used to verify that nobody uses * non-initialized list entries. */ -#define LIST_POISON1 ((void *) 0x00100100) -#define LIST_POISON2 ((void *) 0x00200200) +#define LIST_POISON1 ((void *) 0x00100100 + POISON_POINTER_DELTA) +#define LIST_POISON2 ((void *) 0x00200200 + POISON_POINTER_DELTA) /********** include/linux/timer.h **********/ /* -- 1.5.5.1
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