Re: [2/2] x86/unwind: Make CONFIG_UNWINDER_ORC=y the default in kconfig for 64-bit
From: Andrei Vagin
Date: Thu Oct 19 2017 - 18:35:46 EST
On Thu, Oct 19, 2017 at 01:16:55PM -0500, Josh Poimboeuf wrote:
> On Thu, Oct 19, 2017 at 09:51:04AM -0700, Andrei Vagin wrote:
> > Hi,
> >
> > We run CRIU tests for tip/auto-latest regularly, and a few days ago our
> > test job started to detect this warning in a kernel log:
> >
> > [ 44.235786] WARNING: can't dereference iret registers at ffff8801c5f17fe0 for ip ffffffff95f0d94b
> >
> > What does it mean? How critical is it?
> >
> > Our test job fails if it detects any warning in a kernel log. Maybe we
> > need to investigate reasons of this warning and try to eliminate it?
> >
> > Here are logs:
> > https://travis-ci.org/avagin/linux/jobs/289676634
>
> I think it means the unwinder found some bad ORC unwinder metadata. Any
> chance you have access to the kernel binary? I need to know what code
> corresponds to that ffffffff95f0d94b address.
>
> Or if you can reproduce with the following patch, that should help:
>
>
> diff --git a/arch/x86/kernel/unwind_orc.c b/arch/x86/kernel/unwind_orc.c
> index 570b70d3f604..95b633f0ce51 100644
> --- a/arch/x86/kernel/unwind_orc.c
> +++ b/arch/x86/kernel/unwind_orc.c
> @@ -448,7 +448,7 @@ bool unwind_next_frame(struct unwind_state *state)
>
> case ORC_TYPE_REGS_IRET:
> if (!deref_stack_regs(state, sp, &state->ip, &state->sp, false)) {
> - orc_warn("can't dereference iret registers at %p for ip %p\n",
> + orc_warn("can't dereference iret registers at %p for ip %pB\n",
> (void *)sp, (void *)orig_ip);
> goto done;
> }
I applied your patch and rerun tests.
[ 44.947699] WARNING: can't dereference iret registers at ffff880178f5ffe0 for ip int3+0x5b/0x60
and now here is a warning from kasan:
[ 477.775676] ==================================================================
[ 477.775845] BUG: KASAN: stack-out-of-bounds in deref_stack_reg+0x11d/0x150
[ 477.775952] Read of size 8 at addr ffff880166b7fe90 by task make/16028
[ 477.776055]
[ 477.776149] CPU: 0 PID: 16028 Comm: make Not tainted 4.14.0-rc5+ #1
[ 477.776152] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
[ 477.776155] Call Trace:
[ 477.776159] <IRQ>
[ 477.776167] dump_stack+0x5c/0x7e
[ 477.776175] print_address_description+0x6b/0x290
[ 477.776182] ? deref_stack_reg+0x11d/0x150
[ 477.776186] kasan_report+0x25d/0x340
[ 477.776194] deref_stack_reg+0x11d/0x150
[ 477.776201] ? __read_once_size_nocheck.constprop.6+0x10/0x10
[ 477.776206] ? get_stack_info+0x37/0x170
[ 477.776212] ? stack_access_ok+0xdc/0x150
[ 477.776221] unwind_next_frame+0xe35/0x1c10
[ 477.776230] ? do_execveat_common.isra.34+0x78e/0x1890
[ 477.776238] ? deref_stack_reg+0x150/0x150
[ 477.776247] ? is_bpf_text_address+0x54/0x60
[ 477.776253] ? kernel_text_address+0xf4/0x100
[ 477.776257] ? do_execveat_common.isra.34+0x78e/0x1890
[ 477.776266] __save_stack_trace+0x73/0xd0
[ 477.776277] ? do_execveat_common.isra.34+0x78e/0x1890
[ 477.776285] save_stack+0x33/0xb0
[ 477.776291] ? kasan_slab_free+0x70/0xc0
[ 477.776298] ? kmem_cache_free+0x9f/0x230
[ 477.776303] ? rcu_process_callbacks+0x451/0xd60
[ 477.776307] ? __do_softirq+0x1d3/0x5e0
[ 477.776312] ? irq_exit+0x146/0x170
[ 477.776322] ? smp_apic_timer_interrupt+0x13e/0x3b0
[ 477.776326] ? apic_timer_interrupt+0x8c/0xa0
[ 477.776331] ? lock_acquire+0x6b/0x260
[ 477.776336] ? do_execveat_common.isra.34+0x78e/0x1890
[ 477.776347] ? update_curr+0x2d6/0x600
[ 477.776354] ? posix_cpu_timers_exit_group+0x50/0x50
[ 477.776365] ? trigger_load_balance+0x1fd/0x8a0
[ 477.776374] ? note_gp_changes+0x14e/0x1b0
[ 477.776384] ? lock_downgrade+0x590/0x590
[ 477.776389] ? rcu_accelerate_cbs+0x106/0x5e0
[ 477.776398] ? lock_acquire+0x113/0x260
[ 477.776402] ? rcu_process_callbacks+0x407/0xd60
[ 477.776407] kasan_slab_free+0x70/0xc0
[ 477.776414] ? rcu_process_callbacks+0x451/0xd60
[ 477.776418] kmem_cache_free+0x9f/0x230
[ 477.776425] ? free_inode_nonrcu+0x20/0x20
[ 477.776430] rcu_process_callbacks+0x451/0xd60
[ 477.776443] ? note_gp_changes+0x1b0/0x1b0
[ 477.776451] ? native_apic_msr_write+0x27/0x30
[ 477.776456] ? lapic_next_event+0x55/0x80
[ 477.776465] __do_softirq+0x1d3/0x5e0
[ 477.776479] ? do_execveat_common.isra.34+0x78e/0x1890
[ 477.776483] irq_exit+0x146/0x170
[ 477.776487] smp_apic_timer_interrupt+0x13e/0x3b0
[ 477.776494] apic_timer_interrupt+0x8c/0xa0
[ 477.776497] </IRQ>
[ 477.776502] RIP: 0010:lock_acquire+0x6b/0x260
[ 477.776505] RSP: 0018:ffff880166b7fd48 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff11
[ 477.776512] RAX: 0000000000000007 RBX: ffff8801c91cb080 RCX: 0000000000000000
[ 477.776515] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff8801c91cb8b4
[ 477.776518] RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000000
[ 477.776521] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
[ 477.776524] R13: 0000000000000000 R14: 0000000000000000 R15: ffffffff9f651fce
[ 477.776528] ? do_execveat_common.isra.34+0x78e/0x1890
[ 477.776552] do_execveat_common.isra.34+0x78e/0x1890
[ 477.776559] ? fs_reclaim_acquire.part.71+0x29/0x30
[ 477.776564] ? fs_reclaim_acquire.part.71+0x5/0x30
[ 477.776569] ? kmem_cache_alloc+0x29/0x1f0
[ 477.776577] ? do_execveat_common.isra.34+0x78e/0x1890
[ 477.776589] ? strncpy_from_user+0x74/0x260
[ 477.776595] ? prepare_bprm_creds+0x100/0x100
[ 477.776599] ? kmem_cache_alloc+0x18d/0x1f0
[ 477.776607] ? getname_flags+0xff/0x500
[ 477.776615] ? SyS_execve+0x2c/0x40
[ 477.776623] ? ptregs_sys_vfork+0x10/0x10
[ 477.776628] ? do_syscall_64+0x181/0x450
[ 477.776638] ? entry_SYSCALL64_slow_path+0x25/0x25
[ 477.776653]
[ 477.776747] The buggy address belongs to the page:
[ 477.776849] page:ffffea00059adfc0 count:0 mapcount:0 mapping: (null) index:0x0
[ 477.776968] flags: 0x17fff8000000000()
[ 477.777067] raw: 017fff8000000000 0000000000000000 0000000000000000 00000000ffffffff
[ 477.777184] raw: 0000000000000000 dead000000000200 0000000000000000 0000000000000000
[ 477.777298] page dumped because: kasan: bad access detected
[ 477.777404]
[ 477.777494] Memory state around the buggy address:
[ 477.777594] ffff880166b7fd80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[ 477.777709] ffff880166b7fe00: 00 00 00 00 00 00 00 00 00 00 00 f1 f1 f1 f1 00
[ 477.777823] >ffff880166b7fe80: f4 f4 f4 f3 f3 f3 f3 00 00 00 00 00 00 00 00 00
[ 477.777937] ^
[ 477.778034] ffff880166b7ff00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[ 477.778147] ffff880166b7ff80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[ 477.778260] ==================================================================
[ 477.778376] Disabling lock debugging due to kernel taint
All logs are here https://travis-ci.org/avagin/linux/jobs/290190646
Unfortunately vmlinux was not saved for this run. Thanks.