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Date:   Wed, 12 Aug 2020 10:18:32 +0200
From:   peterz@infradead.org
To:     Marco Elver <elver@google.com>
Cc:     =?iso-8859-1?Q?J=FCrgen_Gro=DF?= <jgross@suse.com>,
        Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        fenghua.yu@intel.com, "H. Peter Anvin" <hpa@zytor.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@redhat.com>,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        "Luck, Tony" <tony.luck@intel.com>,
        the arch/x86 maintainers <x86@kernel.org>,
        yu-cheng.yu@intel.com, sdeep@vmware.com,
        virtualization@lists.linux-foundation.org,
        kasan-dev <kasan-dev@googlegroups.com>,
        syzbot <syzbot+8db9e1ecde74e590a657@syzkaller.appspotmail.com>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        Wei Liu <wei.liu@kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH] x86/paravirt: Add missing noinstr to arch_local*()
 helpers
Message-ID: <20200812081832.GK2674@hirez.programming.kicks-ass.net>
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On Wed, Aug 12, 2020 at 10:06:50AM +0200, Marco Elver wrote:
> On Tue, Aug 11, 2020 at 10:17PM +0200, peterz@infradead.org wrote:
> > On Tue, Aug 11, 2020 at 11:46:51AM +0200, peterz@infradead.org wrote:
> > 
> > > So let me once again see if I can't find a better solution for this all.
> > > Clearly it needs one :/
> > 
> > So the below boots without triggering the debug code from Marco -- it
> > should allow nesting local_irq_save/restore under raw_local_irq_*().
> > 
> > I tried unconditional counting, but there's some _reallly_ wonky /
> > asymmetric code that wrecks that and I've not been able to come up with
> > anything useful.
> > 
> > This one starts counting when local_irq_save() finds it didn't disable
> > IRQs while lockdep though it did. At that point, local_irq_restore()
> > will decrement and enable things again when it reaches 0.
> > 
> > This assumes local_irq_save()/local_irq_restore() are nested sane, which
> > is mostly true.
> > 
> > This leaves #PF, which I fixed in these other patches, but I realized it
> > needs fixing for all architectures :-( No bright ideas there yet.
> > 
> > ---
> >  arch/x86/entry/thunk_32.S       |  5 ----
> >  include/linux/irqflags.h        | 45 +++++++++++++++++++-------------
> >  init/main.c                     | 16 ++++++++++++
> >  kernel/locking/lockdep.c        | 58 +++++++++++++++++++++++++++++++++++++++++
> >  kernel/trace/trace_preemptirq.c | 33 +++++++++++++++++++++++
> >  5 files changed, 134 insertions(+), 23 deletions(-)
> 
> Testing this again with syzkaller produced some new reports:
> 
> 	BUG: stack guard page was hit in error_entry
> 	BUG: stack guard page was hit in exc_int3
> 	PANIC: double fault in error_entry
> 	PANIC: double fault in exc_int3
> 
> Most of them have corrupted reports, but this one might be useful:
> 
> 	BUG: stack guard page was hit at 000000001fab0982 (stack is 00000000063f33dc..00000000bf04b0d8)
> 	BUG: stack guard page was hit at 00000000ca97ac69 (stack is 00000000af3e6c84..000000001597e1bf)
> 	kernel stack overflow (double-fault): 0000 [#1] PREEMPT SMP
> 	CPU: 1 PID: 4709 Comm: kworker/1:1H Not tainted 5.8.0+ #5
> 	Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1 04/01/2014
> 	Workqueue: events_highpri snd_vmidi_output_work
> 	RIP: 0010:exc_int3+0x5/0xf0 arch/x86/kernel/traps.c:636
> 	Code: c9 85 4d 89 e8 31 c0 e8 a9 7d 68 fd e9 90 fe ff ff e8 0f 35 00 00 66 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 55 53 48 89 fb <e8> 76 0e 00 00 85 c0 74 03 5b 5d c3 f6 83 88 00 00 00 03 74 7e 48
> 	RSP: 0018:ffffc90008114000 EFLAGS: 00010083
> 	RAX: 0000000084e00e17 RBX: ffffc90008114018 RCX: ffffffff84e00e17
> 	RDX: 0000000000000000 RSI: ffffffff84e00a39 RDI: ffffc90008114018
> 	RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
> 	R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
> 	R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
> 	FS:  0000000000000000(0000) GS:ffff88807dc80000(0000) knlGS:0000000000000000
> 	CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> 	CR2: ffffc90008113ff8 CR3: 000000002dae4006 CR4: 0000000000770ee0
> 	DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> 	DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> 	PKRU: 00000000
> 	Call Trace:
> 	 asm_exc_int3+0x31/0x40 arch/x86/include/asm/idtentry.h:537
> 	RIP: 0010:arch_static_branch include/trace/events/preemptirq.h:40 [inline]
> 	RIP: 0010:static_key_false include/linux/jump_label.h:200 [inline]
> 	RIP: 0010:trace_irq_enable_rcuidle+0xd/0x120 include/trace/events/preemptirq.h:40
> 	Code: 24 08 48 89 df e8 43 8d ef ff 48 89 df 5b e9 4a 2e 99 03 66 2e 0f 1f 84 00 00 00 00 00 55 41 56 53 48 89 fb e8 84 1a fd ff cc <1f> 44 00 00 5b 41 5e 5d c3 65 8b 05 ab 74 c3 7e 89 c0 31 f6 48 0f
> 	RSP: 0018:ffffc900081140f8 EFLAGS: 00000093
> 	RAX: ffffffff813d9e8c RBX: ffffffff81314dd3 RCX: ffff888076ce6000
> 	RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffffff81314dd3
> 	RBP: 0000000000000000 R08: ffffffff813da3d4 R09: 0000000000000001
> 	R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
> 	R13: 0000000000000082 R14: 0000000000000000 R15: ffff888076ce6000
> 	 trace_hardirqs_restore+0x59/0x80 kernel/trace/trace_preemptirq.c:106
> 	 rcu_irq_enter_irqson+0x43/0x70 kernel/rcu/tree.c:1074
> 	 trace_irq_enable_rcuidle+0x87/0x120 include/trace/events/preemptirq.h:40
> 	 trace_hardirqs_restore+0x59/0x80 kernel/trace/trace_preemptirq.c:106
> 	 rcu_irq_enter_irqson+0x43/0x70 kernel/rcu/tree.c:1074
> 	 trace_irq_enable_rcuidle+0x87/0x120 include/trace/events/preemptirq.h:40
> 	 trace_hardirqs_restore+0x59/0x80 kernel/trace/trace_preemptirq.c:106
> 	 rcu_irq_enter_irqson+0x43/0x70 kernel/rcu/tree.c:1074
> 	 trace_irq_enable_rcuidle+0x87/0x120 include/trace/events/preemptirq.h:40
> 	 trace_hardirqs_restore+0x59/0x80 kernel/trace/trace_preemptirq.c:106
> 	 rcu_irq_enter_irqson+0x43/0x70 kernel/rcu/tree.c:1074
> 
> 	<... repeated many many times ...>
> 
> 	 trace_irq_enable_rcuidle+0x87/0x120 include/trace/events/preemptirq.h:40
> 	 trace_hardirqs_restore+0x59/0x80 kernel/trace/trace_preemptirq.c:106
> 	 rcu_irq_enter_irqson+0x43/0x70 kernel/rcu/tree.c:1074
> 	Lost 500 message(s)!
> 	BUG: stack guard page was hit at 00000000cab483ba (stack is 00000000b1442365..00000000c26f9ad3)
> 	BUG: stack guard page was hit at 00000000318ff8d8 (stack is 00000000fd87d656..0000000058100136)
> 	---[ end trace 4157e0bb4a65941a ]---

Wheee... recursion! Let me try and see if I can make something of that.