Dmitry Vyukov wrote: > On Tue, Dec 19, 2017 at 2:22 PM, Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote: > >> > >> This BUG is reporting > >> > >> > >> > >> [ 26.089789] usercopy: kernel memory overwrite attempt detected to 0000000022a5b430 (kmalloc-1024) (1024 bytes) > >> > >> > >> > >> line. But isn't 0000000022a5b430 strange for kmalloc(1024, GFP_KERNEL)ed kernel address? > >> > > > >> > > The address is hashed (see the %p threads for 4.15). > >> > > >> > > >> > +Tobin, is there a way to disable hashing entirely? The only > >> > designation of syzbot is providing crash reports to kernel developers > >> > with as much info as possible. It's fine for it to leak whatever. > >> > >> We have new specifier %px to print addresses in hex if leaking info is > >> not a worry. > > > > Could we have a way to know that the printed address is hashed and not just > > a pointer getting completely scrogged? Perhaps prefix it with ... a hash! > > So this line would look like: > > > > [ 26.089789] usercopy: kernel memory overwrite attempt detected to #0000000022a5b430 (kmalloc-1024) (1024 bytes) > > > > Or does that miss the point of hashing the address, so the attacker > > thinks its a real address? > > If we do something with this, I would suggest that we just disable > hashing. Any of the concerns that lead to hashed pointers are not > applicable in this context, moreover they are harmful, cause confusion > and make it harder to debug these bugs. That perfectly can be an > opt-in CONFIG_DEBUG_INSECURE_BLA_BLA_BLA. > Why not a kernel command line option? Hashing by default. -- 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>
