On 8/9/19 4:46 AM, Matthew Wilcox wrote: > On Fri, Aug 09, 2019 at 09:08:37AM +0800, miles.chen@xxxxxxxxxxxx wrote: >> Possible approaches are: >> 1. stop printing kernel addresses >> 2. print with %pK, >> 3. print with %px. > > No. The point of obscuring kernel addresses is that if the attacker manages to find a way to get the kernel to spit out some debug messages that we shouldn't > leak all this extra information. On the other hand, while CONFIG_SLUB_DEBUG=y is common, the actual checks and printing happens when the (relatively expensive) checks are actually enabled during boot, i.e. during a debugging session, not production defaults. I can see how knowing the exact address might be useful when e.g. a crash dump is also taken. I would say %pK would be a good fit, if kptr_restrict also had a setting that makes %pK behave like %px (looks like it doesn't), so that setting would be enabled in such a debugging session. >> 4. do nothing > > 5. Find something more useful to print. > >> INFO: Slab 0x(____ptrval____) objects=25 used=10 fp=0x(____ptrval____) > > ... you don't have any randomness on your platform? > >> INFO: Object 0x(____ptrval____) @offset=1408 fp=0x(____ptrval____) >> Redzone (____ptrval____): bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb >> Redzone (____ptrval____): bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb >> Redzone (____ptrval____): bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb >> Redzone (____ptrval____): bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb >> Redzone (____ptrval____): bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb >> Redzone (____ptrval____): bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb >> Redzone (____ptrval____): bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb >> Redzone (____ptrval____): bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb >> Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b >> Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b >> Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b >> Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b >> Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b >> Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b >> Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b >> Object (____ptrval____): 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b a5 >> Redzone (____ptrval____): bb bb bb bb bb bb bb bb >> Padding (____ptrval____): 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a >> Padding (____ptrval____): 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a >> Padding (____ptrval____): 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a >> Padding (____ptrval____): 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a >> ... >> FIX kmalloc-128: Object at 0x(____ptrval____) not freed > > But if you have randomness, at least some of these "pointers" are valuable > because you can compare them against "pointers" printed by other parts > of the kernel. > >> After this patch: >> >> INFO: Slab 0xffffffbf00f57000 objects=25 used=23 fp=0xffffffc03d5c3500 >> INFO: Object 0xffffffc03d5c3500 @offset=13568 fp=0xffffffc03d5c0800 >> Redzone 00000000: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb >> Redzone 00000010: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb >> Redzone 00000020: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb >> Redzone 00000030: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb >> Redzone 00000040: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb >> Redzone 00000050: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb >> Redzone 00000060: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb >> Redzone 00000070: bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb bb >> Object 00000000: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b >> Object 00000010: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b >> Object 00000020: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b >> Object 00000030: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b >> Object 00000040: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b >> Object 00000050: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b >> Object 00000060: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b >> Object 00000070: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b a5 >> Redzone 00000000: bb bb bb bb bb bb bb bb >> Padding 00000000: 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a >> Padding 00000010: 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a >> Padding 00000020: 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a >> Padding 00000030: 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a 5a >> ... >> FIX kmalloc-128: Object at 0xffffffc03d5c3500 not freed > > It looks prettier, but I'm not convinced it's more useful. Unless your > platform lacks randomness ... >
