linux-kernel - Re: [PATCH] driver core: auxiliary bus: Fix calling stage for auxiliary bus init

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Date:   Tue, 9 Feb 2021 20:55:25 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Dave Jiang <dave.jiang@...el.com>
Cc:     Jacob Pan <jacob.jun.pan@...el.com>,
        Dave Ertman <david.m.ertman@...el.com>,
        Dan Williams <dan.j.williams@...el.com>, rafael@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] driver core: auxiliary bus: Fix calling stage for
 auxiliary bus init

On Tue, Feb 09, 2021 at 12:38:06PM -0700, Dave Jiang wrote:
> 
> On 2/9/2021 12:14 PM, Greg KH wrote:
> > On Tue, Feb 09, 2021 at 12:05:05PM -0700, Dave Jiang wrote:
> > > When the auxiliary device code is built into the kernel, it can be executed
> > > before the auxiliary bus is registered. This causes bus->p to be not
> > > allocated and triggers a NULL pointer dereference when the auxiliary bus
> > > device gets added with bus_add_device(). Change the init of auxiliary bus
> > > to subsys_initcall() from module_init() to ensure the bus is registered
> > > before devices.
> > > 
> > > Below is the kernel splat for the bug:
> > > [ 1.948215] BUG: kernel NULL pointer dereference, address: 0000000000000060
> > > [ 1.950670] #PF: supervisor read access in kernel mode
> > > [ 1.950670] #PF: error_code(0x0000) - not-present page
> > > [ 1.950670] PGD 0
> > > [ 1.950670] Oops: 0000 1 SMP NOPTI
> > > [ 1.950670] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.10.0-intel-nextsvmtest+ #2205
> > > [ 1.950670] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014
> > > [ 1.950670] RIP: 0010:bus_add_device+0x64/0x140
> > > [ 1.950670] Code: 00 49 8b 75 20 48 89 df e8 59 a1 ff ff 41 89 c4 85 c0 75 7b 48 8b 53 50 48 85 d2 75 03 48 8b 13 49 8b 85 a0 00 00 00 48 89 de <48> 8
> > > 78 60 48 83 c7 18 e8 ef d9 a9 ff 41 89 c4 85 c0 75 45 48 8b
> > > [ 1.950670] RSP: 0000:ff46032ac001baf8 EFLAGS: 00010246
> > > [ 1.950670] RAX: 0000000000000000 RBX: ff4597f7414aa680 RCX: 0000000000000000
> > > [ 1.950670] RDX: ff4597f74142bbc0 RSI: ff4597f7414aa680 RDI: ff4597f7414aa680
> > > [ 1.950670] RBP: ff46032ac001bb10 R08: 0000000000000044 R09: 0000000000000228
> > > [ 1.950670] R10: ff4597f741141b30 R11: ff4597f740182a90 R12: 0000000000000000
> > > [ 1.950670] R13: ffffffffa5e936c0 R14: 0000000000000000 R15: 0000000000000000
> > > [ 1.950670] FS: 0000000000000000(0000) GS:ff4597f7bba00000(0000) knlGS:0000000000000000
> > > [ 1.950670] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > > [ 1.950670] CR2: 0000000000000060 CR3: 000000002140c001 CR4: 0000000000f71ef0
> > > [ 1.950670] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > > [ 1.950670] DR3: 0000000000000000 DR6: 00000000fffe07f0 DR7: 0000000000000400
> > > [ 1.950670] PKRU: 55555554
> > > [ 1.950670] Call Trace:
> > > [ 1.950670] device_add+0x3ee/0x850
> > > [ 1.950670] __auxiliary_device_add+0x47/0x60
> > > [ 1.950670] idxd_pci_probe+0xf77/0x1180
> > > [ 1.950670] local_pci_probe+0x4a/0x90
> > > [ 1.950670] pci_device_probe+0xff/0x1b0
> > > [ 1.950670] really_probe+0x1cf/0x440
> > > [ 1.950670] ? rdinit_setup+0x31/0x31
> > > [ 1.950670] driver_probe_device+0xe8/0x150
> > > [ 1.950670] device_driver_attach+0x58/0x60
> > > [ 1.950670] __driver_attach+0x8f/0x150
> > > [ 1.950670] ? device_driver_attach+0x60/0x60
> > > [ 1.950670] ? device_driver_attach+0x60/0x60
> > > [ 1.950670] bus_for_each_dev+0x79/0xc0
> > > [ 1.950670] ? kmem_cache_alloc_trace+0x323/0x430
> > > [ 1.950670] driver_attach+0x1e/0x20
> > > [ 1.950670] bus_add_driver+0x154/0x1f0
> > > [ 1.950670] driver_register+0x70/0xc0
> > > [ 1.950670] __pci_register_driver+0x54/0x60
> > > [ 1.950670] idxd_init_module+0xe2/0xfc
> > > [ 1.950670] ? idma64_platform_driver_init+0x19/0x19
> > > [ 1.950670] do_one_initcall+0x4a/0x1e0
> > > [ 1.950670] kernel_init_freeable+0x1fc/0x25c
> > > [ 1.950670] ? rest_init+0xba/0xba
> > > [ 1.950670] kernel_init+0xe/0x116
> > > [ 1.950670] ret_from_fork+0x1f/0x30
> > > [ 1.950670] Modules linked in:
> > > [ 1.950670] CR2: 0000000000000060
> > > [ 1.950670] --[ end trace cd7d1b226d3ca901 ]--
> > > 
> > > Fixes: 7de3697e9cbd ("Add auxiliary bus support")
> > > Reported-by: Jacob Pan <jacob.jun.pan@...el.com>
> > > Acked-by: Dave Ertman <david.m.ertman@...el.com>
> > > Reviewed-by: Dan Williams <dan.j.williams@...el.com>
> > > Signed-off-by: Dave Jiang <dave.jiang@...el.com>
> > > ---
> > >   drivers/base/auxiliary.c |    2 +-
> > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/base/auxiliary.c b/drivers/base/auxiliary.c
> > > index 8336535f1e11..53f93a506626 100644
> > > --- a/drivers/base/auxiliary.c
> > > +++ b/drivers/base/auxiliary.c
> > > @@ -270,7 +270,7 @@ static void __exit auxiliary_bus_exit(void)
> > >   	bus_unregister(&auxiliary_bus_type);
> > >   }
> > > -module_init(auxiliary_bus_init);
> > > +subsys_initcall(auxiliary_bus_init);
> > Ah, the linker priority dance.  Are you _SURE_ this will solve this?
> > 
> > Why not just call this explicitly in driver_init() so that you know it
> > will be ok?  Just like we do for the platform bus?
> 
> It would require making auxiliary_bus part of the base just like platform
> instead of a module.

The auxiliary_bus code is not a module today, so I have no idea what
you are talking about, sorry.

> Is that ok?

No it is not.

greg k-h