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: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Jaswinder Singh Rajput <jaswinderrajput@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 6bf1f1a..cbcbfde 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1247,6 +1247,11 @@
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