On Tue, 27 Jul 2021 at 10:32, Kuan-Ying Lee <Kuan-Ying.Lee@xxxxxxxxxxxx> wrote: > > On Tue, 2021-07-27 at 09:10 +0200, Marco Elver wrote: > > +Cc Catalin > > > > On Tue, 27 Jul 2021 at 06:00, Kuan-Ying Lee < > > Kuan-Ying.Lee@xxxxxxxxxxxx> wrote: > > > > > > Hardware tag-based KASAN doesn't use compiler instrumentation, we > > > can not use kasan_disable_current() to ignore tag check. > > > > > > Thus, we need to reset tags when accessing metadata. > > > > > > Signed-off-by: Kuan-Ying Lee <Kuan-Ying.Lee@xxxxxxxxxxxx> > > > > This looks reasonable, but the patch title is not saying this is > > kmemleak, nor does the description say what the problem is. What > > problem did you encounter? Was it a false positive? > > kmemleak would scan kernel memory to check memory leak. > When it scans on the invalid slab and dereference, the issue > will occur like below. Please also add this info to commit message. > So I think we should reset the tag before scanning. > > # echo scan > /sys/kernel/debug/kmemleak > [ 151.905804] > ================================================================== > [ 151.907120] BUG: KASAN: out-of-bounds in scan_block+0x58/0x170 > [ 151.908773] Read at addr f7ff0000c0074eb0 by task kmemleak/138 > [ 151.909656] Pointer tag: [f7], memory tag: [fe] > [ 151.910195] > [ 151.910876] CPU: 7 PID: 138 Comm: kmemleak Not tainted 5.14.0-rc2- > 00001-g8cae8cd89f05-dirty #134 > [ 151.912085] Hardware name: linux,dummy-virt (DT) > [ 151.912868] Call trace: > [ 151.913211] dump_backtrace+0x0/0x1b0 > [ 151.913796] show_stack+0x1c/0x30 > [ 151.914248] dump_stack_lvl+0x68/0x84 > [ 151.914778] print_address_description+0x7c/0x2b4 > [ 151.915340] kasan_report+0x138/0x38c > [ 151.915804] __do_kernel_fault+0x190/0x1c4 > [ 151.916386] do_tag_check_fault+0x78/0x90 > [ 151.916856] do_mem_abort+0x44/0xb4 > [ 151.917308] el1_abort+0x40/0x60 > [ 151.917754] el1h_64_sync_handler+0xb4/0xd0 > [ 151.918270] el1h_64_sync+0x78/0x7c > [ 151.918714] scan_block+0x58/0x170 > [ 151.919157] scan_gray_list+0xdc/0x1a0 > [ 151.919626] kmemleak_scan+0x2ac/0x560 > [ 151.920129] kmemleak_scan_thread+0xb0/0xe0 > [ 151.920635] kthread+0x154/0x160 > [ 151.921115] ret_from_fork+0x10/0x18 > [ 151.921717] > [ 151.922077] Allocated by task 0: > [ 151.922523] kasan_save_stack+0x2c/0x60 > [ 151.923099] __kasan_kmalloc+0xec/0x104 > [ 151.923502] __kmalloc+0x224/0x3c4 > [ 151.924172] __register_sysctl_paths+0x200/0x290 > [ 151.924709] register_sysctl_table+0x2c/0x40 > [ 151.925175] sysctl_init+0x20/0x34 > [ 151.925665] proc_sys_init+0x3c/0x48 > [ 151.926136] proc_root_init+0x80/0x9c > [ 151.926547] start_kernel+0x648/0x6a4 > [ 151.926987] __primary_switched+0xc0/0xc8 > [ 151.927557] > [ 151.927994] Freed by task 0: > [ 151.928340] kasan_save_stack+0x2c/0x60 > [ 151.928766] kasan_set_track+0x2c/0x40 > [ 151.929173] kasan_set_free_info+0x44/0x54 > [ 151.929568] ____kasan_slab_free.constprop.0+0x150/0x1b0 > [ 151.930063] __kasan_slab_free+0x14/0x20 > [ 151.930449] slab_free_freelist_hook+0xa4/0x1fc > [ 151.930924] kfree+0x1e8/0x30c > [ 151.931285] put_fs_context+0x124/0x220 > [ 151.931731] vfs_kern_mount.part.0+0x60/0xd4 > [ 151.932280] kern_mount+0x24/0x4c > [ 151.932686] bdev_cache_init+0x70/0x9c > [ 151.933122] vfs_caches_init+0xdc/0xf4 > [ 151.933578] start_kernel+0x638/0x6a4 > [ 151.934014] __primary_switched+0xc0/0xc8 > [ 151.934478] > [ 151.934757] The buggy address belongs to the object at > ffff0000c0074e00 > [ 151.934757] which belongs to the cache kmalloc-256 of size 256 > [ 151.935744] The buggy address is located 176 bytes inside of > [ 151.935744] 256-byte region [ffff0000c0074e00, ffff0000c0074f00) > [ 151.936702] The buggy address belongs to the page: > [ 151.937378] page:(____ptrval____) refcount:1 mapcount:0 > mapping:0000000000000000 index:0x0 pfn:0x100074 > [ 151.938682] head:(____ptrval____) order:2 compound_mapcount:0 > compound_pincount:0 > [ 151.939440] flags: > 0xbfffc0000010200(slab|head|node=0|zone=2|lastcpupid=0xffff|kasantag=0x > 0) > [ 151.940886] raw: 0bfffc0000010200 0000000000000000 dead000000000122 > f5ff0000c0002300 > [ 151.941634] raw: 0000000000000000 0000000000200020 00000001ffffffff > 0000000000000000 > [ 151.942353] page dumped because: kasan: bad access detected > [ 151.942923] > [ 151.943214] Memory state around the buggy address: > [ 151.943896] ffff0000c0074c00: f0 f0 f0 f0 f0 f0 f0 f0 f0 fe fe fe > fe fe fe fe > [ 151.944857] ffff0000c0074d00: fe fe fe fe fe fe fe fe fe fe fe fe > fe fe fe fe > [ 151.945892] >ffff0000c0074e00: f7 f7 f7 f7 f7 f7 f7 f7 f7 f7 f7 fe > fe fe fe fe > [ 151.946407] ^ > [ 151.946939] ffff0000c0074f00: fe fe fe fe fe fe fe fe fe fe fe fe > fe fe fe fe > [ 151.947445] ffff0000c0075000: fb fb fb fb fb fb fb fb fb fb fb fb > fb fb fb fb > [ 151.947999] > ================================================================== > [ 151.948524] Disabling lock debugging due to kernel taint > [ 156.434569] kmemleak: 181 new suspected memory leaks (see > /sys/kernel/debug/kmemleak) > > > > > Perhaps this should have been "kmemleak, kasan: reset pointer tags to > > avoid false positives" ? > > Thanks for the suggestions. > But I think it doesn't belong to false > positive becuase scan block > touched invalid metadata certainly. It's how kmemleak works, so we knowingly access invalid memory, and for all intents and purposes it's a false positive. > Maybe "kmemleak, kasan: reset tags when scanning block"? That's fine. Thanks, -- Marco
