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Commit a29815a3 authored by Avi Kivity's avatar Avi Kivity Committed by Linus Torvalds
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core, x86: make LIST_POISON less deadly 



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-undereferencable values.
This is easy on x86_64 as the virtual address space is large and contains
areas that cannot be mapped.

Other 64-bit architectures will likely find similar unmapped ranges.

[ingo: switch to 0xdead000000000000 as the unmapped area]
[ingo: add comments, cleanup]
[jaswinder: eliminate sparse warnings]

Acked-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: default avatarJaswinder Singh Rajput <jaswinderrajput@gmail.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
Signed-off-by: default avatarAvi Kivity <avi@redhat.com>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent c0f607c6

arch/x86/Kconfig

+5 −0
Original line number Diff line number Diff line
@@ -1247,6 +1247,11 @@ config ARCH_MEMORY_PROBE 
	def_bool X86_64

	depends on MEMORY_HOTPLUG



config ILLEGAL_POINTER_VALUE

       hex

       default 0 if X86_32

       default 0xdead000000000000 if X86_64



source "mm/Kconfig"



config HIGHPTE

include/linux/poison.h

+14 −2
Original line number Diff line number Diff line
@@ -2,13 +2,25 @@ 
#define _LINUX_POISON_H



/********** include/linux/list.h **********/



/*

 * Architectures might want to move the poison pointer offset

 * into some well-recognized area such as 0xdead000000000000,

 * that is also not mappable by user-space exploits:

 */

#ifdef CONFIG_ILLEGAL_POINTER_VALUE

# define POISON_POINTER_DELTA _AC(CONFIG_ILLEGAL_POINTER_VALUE, UL)

#else

# define POISON_POINTER_DELTA 0

#endif



/*

 * 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 **********/

/*