On Mon, Aug 7, 2017 at 3:00 PM, Laura Abbott <labbott@xxxxxxxxxx> wrote: > On 08/07/2017 11:03 AM, Christopher Lameter wrote: >> On Mon, 7 Aug 2017, Laura Abbott wrote: >> >>>> Ok I see that the objects are initialized with poisoning and redzoning but >>>> I do not see that there is fastpath code to actually check the values >>>> before the object is reinitialized. Is that intentional or am >>>> I missing something? >>> >>> Yes, that's intentional here. I see the validation as a separate more >>> expensive feature. I had a crude patch to do some checks for testing >>> and I know Daniel Micay had an out of tree patch to do some checks >>> as well. >> >> Ok then this patch does nothing? How does this help? > > The purpose of this patch is to ensure the poisoning can happen without > too much penalty. Even if there aren't checks to abort/warn when there > is a problem, there's still value in ensuring objects are always poisoned. To clarify, this is desirable to kill exploitation of exposure-after-free flaws and some classes of use-after-free flaws, since the contents will have be wiped out after a free. (Verification of poison is nice, but is expensive compared to the benefit against these exploits -- and notably doesn't protect against the other use-after-free attacks where the contents are changed after the next allocation, which would have passed the poison verification.) -Kees -- Kees Cook Pixel Security -- 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/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
