Messages in this thread Patch in this message | | | Date | Wed, 11 Apr 2012 02:37:58 +0400 | From | Cyrill Gorcunov <> | Subject | Re: + syscalls-x86-add-__nr_kcmp-syscall-v8.patch added to -mm tree |
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On Mon, Apr 09, 2012 at 04:22:38PM -0700, H. Peter Anvin wrote: > > The obfuscation logic was done with great help from hpa@. And the main > > idea was to have ordered results after obfuscation. Per-type noise increase > > randomization of results. So Andrew, I actually dont know what to add > > here. We don't want to provide kernel order back to user-space in > > naked manner. > > > > The obfuscation logic is to provide a 1:1 mapping but which doesn't > preserve ordering, thereby avoid leaking information of kernel pointers > to user space. >
OK, Peter, would the following comment bring light on the obfuscation procedure? --- Add a comment on kcmp obfuscation method
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org> --- kernel/kcmp.c | 11 +++++++++++ 1 file changed, 11 insertions(+)
Index: linux-2.6.git/kernel/kcmp.c =================================================================== --- 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;
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