Re: [PATCH v4 1/2] x86/unwind: add ORC unwinder

["Levin, Alexander (Sasha Levin)" <alexander.levin@verizon.com>]

On Mon, Jul 24, 2017 at 06:36:57PM -0500, Josh Poimboeuf wrote:
>Add a new ORC unwinder which is enabled by CONFIG_ORC_UNWINDER.  It
>plugs into the existing x86 unwinder framework.
>
>It relies on objtool to generate the needed .orc_unwind and
>.orc_unwind_ip sections.
>
>For more details on why ORC is used instead of DWARF, see
>Documentation/x86/orc-unwinder.txt.
>
>Thanks to Andy Lutomirski for the performance improvement ideas:
>splitting the ORC unwind table into two parallel arrays and creating a
>fast lookup table to search a subset of the unwind table.
>
>Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>

Hey Josh,

Syzkaller seems to trigger the following:

==================================================================
BUG: KASAN: stack-out-of-bounds in __read_once_size include/linux/compiler.h:253 [inline]
BUG: KASAN: stack-out-of-bounds in deref_stack_reg+0x123/0x140 arch/x86/kernel/unwind_orc.c:282
Read of size 8 at addr ffff8800374a7b28 by task syz-executor4/6474

CPU: 2 PID: 6474 Comm: syz-executor4 Not tainted 4.13.0-rc2-next-20170727 #232
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.1-1ubuntu1 04/01/2014
Call Trace:
 <IRQ>
 __dump_stack lib/dump_stack.c:16 [inline]
 dump_stack+0xab/0x105 lib/dump_stack.c:52
 print_address_description+0xc2/0x250 mm/kasan/report.c:252
 kasan_report_error mm/kasan/report.c:351 [inline]
 kasan_report+0x24f/0x360 mm/kasan/report.c:408
 __read_once_size include/linux/compiler.h:253 [inline]
 deref_stack_reg+0x123/0x140 arch/x86/kernel/unwind_orc.c:282
 unwind_next_frame+0xd9b/0x1b80 arch/x86/kernel/unwind_orc.c:426
 __save_stack_trace+0x7d/0xf0 arch/x86/kernel/stacktrace.c:44
 save_stack+0x33/0xa0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_slab_free+0x72/0xc0 mm/kasan/kasan.c:524
 slab_free_hook mm/slub.c:1357 [inline]
 slab_free_freelist_hook mm/slub.c:1379 [inline]
 slab_free mm/slub.c:2955 [inline]
 kmem_cache_free+0xae/0x310 mm/slub.c:2977
 put_pid+0xe2/0x120 kernel/pid.c:246
 __rcu_reclaim kernel/rcu/rcu.h:195 [inline]
 rcu_do_batch kernel/rcu/tree.c:2666 [inline]
 invoke_rcu_callbacks kernel/rcu/tree.c:2920 [inline]
 __rcu_process_callbacks kernel/rcu/tree.c:2887 [inline]
 rcu_process_callbacks+0x599/0x12b0 kernel/rcu/tree.c:2904
 __do_softirq+0x234/0x934 kernel/softirq.c:284
 invoke_softirq kernel/softirq.c:364 [inline]
 irq_exit+0x164/0x190 kernel/softirq.c:405
 exiting_irq arch/x86/include/asm/apic.h:638 [inline]
 smp_apic_timer_interrupt+0x71/0x90 arch/x86/kernel/apic/apic.c:1044
 apic_timer_interrupt+0xb9/0xc0 arch/x86/entry/entry_64.S:793
 </IRQ>
RIP: 0010:arch_local_irq_enable arch/x86/include/asm/paravirt.h:824 [inline]
RIP: 0010:preempt_schedule_irq+0x71/0xd0 kernel/sched/core.c:3579
RSP: 0018:ffff8800374a7958 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff10
RAX: 0000000000000007 RBX: ffffed0006d95808 RCX: 1ffffffff534d022
RDX: 0000000000000000 RSI: ffffffffa7065fe0 RDI: ffff880036cac9a4
RBP: 0000000000000000 R08: ffff88007ffd709c R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffff880036cac040
R13: 00000000000002eb R14: ffff880036cac040 R15: ffff88005fdc2728
 retint_kernel+0x1b/0x2d
RIP: 0010:arch_local_save_flags arch/x86/include/asm/paravirt.h:809 [inline]
RIP: 0010:___might_sleep+0x159/0x480 kernel/sched/core.c:5968
RSP: 0018:ffff8800374a7a28 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff02
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000001
RDX: 1ffff10006d95882 RSI: 00000000ffffffff RDI: ffff880036cac410
RBP: 0000000000000000 R08: ffffffffa3b1546e R09: dffffc0000000000
R10: ffff8800374a7c08 R11: 0000000000000001 R12: ffffffffa7065320
R13: 00000000000002eb R14: ffff880036cac040 R15: ffff88005fdc2728
 ext4_orphan_add+0x34e/0xd70 fs/ext4/namei.c:2801

The buggy address belongs to the page:
page:ffffea0000dd29c0 count:0 mapcount:0 mapping:          (null) index:0x0
flags: 0xfffe0000000000()
raw: 00fffe0000000000 0000000000000000 0000000000000000 00000000ffffffff
raw: 0000000000000000 dead000000000200 0000000000000000 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8800374a7a00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff8800374a7a80: 00 00 00 00 00 00 00 00 f1 f1 f1 f1 00 f4 f4 f4
>ffff8800374a7b00: f2 f2 f2 f2 00 f4 f4 f4 f2 f2 f2 f2 00 00 00 00
                                  ^
 ffff8800374a7b80: 00 f4 f4 f4 00 00 00 00 00 00 00 00 00 00 00 00
 ffff8800374a7c00: 00 00 00 00 00 00 00 00 00 f1 f1 f1 f1 00 00 00
==================================================================

-- 

Thanks,
Sasha