Messages in this thread | | | Date | Wed, 11 Apr 2012 01:08:33 +0200 | From | Oleg Nesterov <> | Subject | Re: + syscalls-x86-add-__nr_kcmp-syscall-v8.patch added to -mm tree |
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On 04/11, Cyrill Gorcunov wrote: > > --- linux-2.6.git.orig/kernel/kcmp.c > +++ linux-2.6.git/kernel/kcmp.c > @@ -17,6 +17,17 @@ > * reasons, still the comparison results should be suitable for > * sorting. Thus, we obfuscate kernel pointers values and compare > * the production instead. > + * > + * The obfuscation is done in two steps. First -- we use xor on > + * kernel pointer with random value, which puts pointer into > + * a new position in reordered space. Second -- we multiply > + * the xor production with big odd random number to permute > + * bits even more (the oddity is important here, it allow > + * us to have meaningful production even if multiplicants > + * are big numbers). > + * > + * Note also the obfuscation itself is invisible to user-space > + * and if needed it can be changed to any suitable scheme. > */ > static unsigned long cookies[KCMP_TYPES][2] __read_mostly;
OK, since this is discussed again...
Can this comment can also explain why do we obfuscate the pointers by type? I mean, I don't really understand why the one-dimensional cookies[2] is "not enough" from security pov.
Oleg.
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