Removing [email protected] from the CC list. On Wed, Oct 11, 2017 at 01:48:58PM -0400, Theodore Ts'o wrote: > On Wed, Oct 11, 2017 at 02:48:16PM +1100, Tobin C. Harding wrote: > > +/* > > + * Obfuscates pointer (algorithm taken from kptr_obfuscate(). See > > kernel/kcmp.c) > > + * v is the pointer value, randval is some random value, oddval is some > > random > > + * odd value. > > + * > > + * The obfuscation is done in two steps. First we xor the kernel pointer > > with > > + * a random value, which puts pointer into a new position in a reordered > > space. > > + * Secondly we multiply the xor production with a large odd random number > > to > > + * permute its bits even more (the odd multiplier guarantees that the > > product > > + * is unique ever after the high bits are truncated, since any odd number > > is > > + * relative prime to 2^n). > > + */ > > Why not just expose kptr_obfusecate() and use it, instead of copying > code? > > Also, I'm nervous about the obfuscation. If the attacker can get a > handful of known "real kernel pointer" and "obfuscated kernel pointer" > values, it wouldn't be that hard for them to be able to reverse > engineer the two secret values. > > Perhaps the argument is "if the attacker can get a _single_ real > kernel address, it's all over anyway", which is probably true for > KASLR, but which might not be true for all attacks. > > Anyway, if you use kptr_obfuscate in kernel/kcmp.c, then if we later > decide that we should change the obfuscation algorithm to something > stronger, we only need to do it in one place. > > - Ted
Thanks Ted, others have misgivings about this method also. The email threads are all a bit mixed up (thansk to my ineptness at posting patches :). FYI, in the other threads Jason A. Donenfel and Linus Torvalds have discussed SipHash as a solution. thanks, Tobin.
