On Thu, Sep 29, 2011 at 20:18 +0400, Vasiliy Kulikov wrote: > On Tue, Sep 27, 2011 at 13:33 -0700, David Rientjes wrote: > > I'd much rather just convert everything to use MB rather than KB so you > > can't determine things at a page level. I think that gets us much closer > > to what the patch is intending to restrict. But I also expect some > > breakage from things that just expect meminfo to be in KB units without > > parsing what the kernel is exporting. > > I'm not convinced with rounding the information to MBs. The attacker > still may fill slabs with new objects to trigger new slab pages > allocations. He will be able to see when this MB-granularity barrier is > overrun thus seeing how many kbs there were before: > > old = new - filled_obj_size_sum > > As `new' is just increased, it means it is known with KB granularity, > not MB. By counting used slab objects he learns filled_obj_size_sum. s/filled_obj_size_sum/old/ of course. > So, rounding gives us nothing, but obscurity. > > Thanks, -- Vasiliy Kulikov http://www.openwall.com - bringing security into open computing environments -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>