linux-kernel - Re: NULL pointer dereference in msi_set_mask

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Message-ID: <fcc2d1b4-8a10-bc8c-9a9c-2b33e6745b04@arm.com>
Date:   Wed, 18 Jul 2018 16:27:57 +0100
From:   Marc Zyngier <marc.zyngier@....com>
To:     Paul Menzel <pmenzel+linux-pci@...gen.mpg.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Bjorn Helgaas <helgaas@...nel.org>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Hiraku Toyooka <hiraku.toyooka@...ertrust.co.jp>,
        Zou Cao <cao.zou@...driver.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Subject: Re: NULL pointer dereference in msi_set_mask_bit

On 18/07/18 16:12, Paul Menzel wrote:
> Dear Thomas, dear Bjorn,
> 
> 
> Thank you for your quick responses.
> 
> 
> On 07/18/18 17:02, Thomas Gleixner wrote:
>> On Wed, 18 Jul 2018, Bjorn Helgaas wrote:
>>> [+cc Marc, Thomas]
>>
>> Uurgh. That's definitely what I need right now ... :)
>>
>>> On Wed, Jul 18, 2018 at 03:28:15PM +0200, Paul Menzel wrote:
>>>>
>>>> 93.885: [   23.020572] BUG: unable to handle kernel NULL pointer dereference at 000000000000003c
>>>> 93.885: [   23.029011] PGD 0 P4D 0 
>>>> 93.885: [   23.031670] Oops: 0000 [#1] SMP NOPTI
>>>> 93.885: [   23.035455] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.18.0-rc5+ #1
>>>> 93.885: [   23.042079] Hardware name: MSI MS-7A37/B350M MORTAR (MS-7A37), BIOS 1.G1 05/17/2018
>>>> 93.886: [   23.049868] RIP: 0010:msi_set_mask_bit+0xe/0x70
>>
>>>> 93.913: [   23.049868] Code: 00 53 48 89 fb e8 12 f8 ff ff 48 89 df 5b e9 c9 fe ff ff 66 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 53 48 8b 47 10 48 8b 58 10 <f6> 43 3c 01 74 3c 8b 15 2e 85 21 01 31 c0 85 d2 75 25 8b 43 38 48
>>
>>   f6 43 3c 01          	testb  $0x1,0x3c(%rbx)
>>
>> That's:
>>
>> 	if (desc->msi_attrib.is_msix)
> 
> Is there a tool to translate that?
> 
>>>> 93.957: [   23.049880] RSP: 0018:ffff9e8e5e803f78 EFLAGS: 00010046
>>>> 93.957: [   23.049881] RAX: ffff9e8e45919000 RBX: 0000000000000000 RCX: 0000000000000000
>>>> 93.958: [   23.049882] RDX: ffff9e8e45919000 RSI: 0000000000000001 RDI: ffff9e8e45919098
>>>> 93.958: [   23.049882] RBP: ffff9e8e45919098 R08: 0000000000000000 R09: 0000000000000000
>>>> 93.958: [   23.049882] R10: 0000000000000000 R11: 0000000000000000 R12: ffff9e8e45919000
>>>> 93.958: [   23.049883] R13: 0000000000000027 R14: 0000000000000000 R15: 0000000000000000
>>>> 93.959: [   23.049884] FS:  0000000000000000(0000) GS:ffff9e8e5e800000(0000) knlGS:0000000000000000
>>>> 93.959: [   23.049884] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>>> 93.959: [   23.049885] CR2: 000000000000003c CR3: 00000003fc5a4000 CR4: 00000000003406f0
>>>> 93.959: [   23.049885] Call Trace:
>>>> 93.959: [   23.049887]  <IRQ>
>>>> 93.960: [   23.049889]  __irq_move_irq+0x3c/0x70
>>>> 93.960: [   23.049892]  apic_ack_irq+0x2b/0x30
>>>> 93.960: [   23.049893]  handle_edge_irq+0x7d/0x1d0
>>>> 93.960: [   23.049895]  handle_irq+0x1f/0x30
>>>> 93.960: [   23.049898]  do_IRQ+0x41/0xc0
>>>> 93.960: [   23.049899]  common_interrupt+0xf/0xf
>>>> 93.961: [   23.049900]  </IRQ>
>>
>> and desc comes from irq_data->common->msi_desc
>>
>> I have no idea how that can happen for an MSI interrupt.
>>
>> Paul, is this reproducible?
> 
> No, unfortunately not. I only hit this once, since I attached the serial
> console.
> 
> But I found others having the same(?) problem [1][2].
> 
> 
> Kind regards,
> 
> Paul
> 
> 
> [1]: https://lkml.org/lkml/2018/1/16/122
>      "[PATCH 0/1] PCI/MSI: add NULL check before use of msi_desc"
> [2]: https://marc.info/?l=linux-kernel&m=151321815226439&w=2
>      "[PATCH] PCI: designware: add a check of msi_desc in irqchip"
> 

This seems to be a very different issue.

These PCI host controllers pre-allocate a bunch of irqdescs which are
not bound to any MSI yet (this occurs much later, when the interrupt is
actually allocated to a device). But the kexec code tries to mask all
interrupts, including some of these half baked interrupts, and bad
things happen. This is very much a case of "don't do that".

Unless I'm grossly mistaken, this isn't what happens in your case (the
interrupt is very much active, but the msi_desc pointer has vanished).

	M.
-- 
Jazz is not dead. It just smells funny...