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. 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. Maybe "kmemleak, kasan: reset tags when scanning block"? > > > --- > > mm/kmemleak.c | 6 +++--- > > 1 file changed, 3 insertions(+), 3 deletions(-) > > > > diff --git a/mm/kmemleak.c b/mm/kmemleak.c > > index 228a2fbe0657..73d46d16d575 100644 > > --- a/mm/kmemleak.c > > +++ b/mm/kmemleak.c > > @@ -290,7 +290,7 @@ static void hex_dump_object(struct seq_file > > *seq, > > warn_or_seq_printf(seq, " hex dump (first %zu bytes):\n", > > len); > > kasan_disable_current(); > > warn_or_seq_hex_dump(seq, DUMP_PREFIX_NONE, HEX_ROW_SIZE, > > - HEX_GROUP_SIZE, ptr, len, HEX_ASCII); > > + HEX_GROUP_SIZE, kasan_reset_tag((void > > *)ptr), len, HEX_ASCII); > > kasan_enable_current(); > > } > > > > @@ -1171,7 +1171,7 @@ static bool update_checksum(struct > > kmemleak_object *object) > > > > kasan_disable_current(); > > kcsan_disable_current(); > > - object->checksum = crc32(0, (void *)object->pointer, > > object->size); > > + object->checksum = crc32(0, kasan_reset_tag((void *)object- > > >pointer), object->size); > > kasan_enable_current(); > > kcsan_enable_current(); > > > > @@ -1246,7 +1246,7 @@ static void scan_block(void *_start, void > > *_end, > > break; > > > > kasan_disable_current(); > > - pointer = *ptr; > > + pointer = *(unsigned long *)kasan_reset_tag((void > > *)ptr); > > kasan_enable_current(); > > > > untagged_ptr = (unsigned long)kasan_reset_tag((void > > *)pointer); > > -- > > 2.18.0 > > > > -- > > You received this message because you are subscribed to the Google > > Groups "kasan-dev" group. > > To unsubscribe from this group and stop receiving emails from it, > > send an email to kasan-dev+unsubscribe@xxxxxxxxxxxxxxxx. > > To view this discussion on the web visit > > https://urldefense.com/v3/__https://groups.google.com/d/msgid/kasan-dev/20210727040021.21371-2-Kuan-Ying.Lee*40mediatek.com__;JQ!!CTRNKA9wMg0ARbw!wNP4ZkYDM7Xvs9xfzKwYuG1X2h9zFqST8_Vm2jSvZUl9BiS8SPFMTvMp3VAPKCnuWELL7Q$ > > .
