Re: [PATCH] phy: tegra: xusb: Fix dangling pointer on probe failure

[Thierry Reding <thierry.reding@gmail.com>]

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On Tue, Oct 13, 2020 at 10:58:20AM +0100, Marc Zyngier wrote:
> If, for some reason, the xusb PHY fails to probe, it leaves
> a dangling pointer attached to the platform device structure.
> 
> This would normally be harmless, but the Tegra XHCI driver then
> goes and extract that pointer from the PHY device. Things go
> downhill from there:
> 
>     8.752082] [004d554e5145533c] address between user and kernel address ranges
> [    8.752085] Internal error: Oops: 96000004 [#1] PREEMPT SMP
> [    8.752088] Modules linked in: max77620_regulator(E+) xhci_tegra(E+) sdhci_tegra(E+) xhci_hcd(E) sdhci_pltfm(E) cqhci(E) fixed(E) usbcore(E) scsi_mod(E) sdhci(E) host1x(E+)
> [    8.752103] CPU: 4 PID: 158 Comm: systemd-udevd Tainted: G S      W   E     5.9.0-rc7-00298-gf6337624c4fe #1980
> [    8.752105] Hardware name: NVIDIA Jetson TX2 Developer Kit (DT)
> [    8.752108] pstate: 20000005 (nzCv daif -PAN -UAO BTYPE=--)
> [    8.752115] pc : kobject_put+0x1c/0x21c
> [    8.752120] lr : put_device+0x20/0x30
> [    8.752121] sp : ffffffc012eb3840
> [    8.752122] x29: ffffffc012eb3840 x28: ffffffc010e82638
> [    8.752125] x27: ffffffc008d56440 x26: 0000000000000000
> [    8.752128] x25: ffffff81eb508200 x24: 0000000000000000
> [    8.752130] x23: ffffff81eb538800 x22: 0000000000000000
> [    8.752132] x21: 00000000fffffdfb x20: ffffff81eb538810
> [    8.752134] x19: 3d4d554e51455300 x18: 0000000000000020
> [    8.752136] x17: ffffffc008d00270 x16: ffffffc008d00c94
> [    8.752138] x15: 0000000000000004 x14: ffffff81ebd4ae90
> [    8.752140] x13: 0000000000000000 x12: ffffff81eb86a4e8
> [    8.752142] x11: ffffff81eb86a480 x10: ffffff81eb862fea
> [    8.752144] x9 : ffffffc01055fb28 x8 : ffffff81eb86a4a8
> [    8.752146] x7 : 0000000000000001 x6 : 0000000000000001
> [    8.752148] x5 : ffffff81dff8bc38 x4 : 0000000000000000
> [    8.752150] x3 : 0000000000000001 x2 : 0000000000000001
> [    8.752152] x1 : 0000000000000002 x0 : 3d4d554e51455300
> [    8.752155] Call trace:
> [    8.752157]  kobject_put+0x1c/0x21c
> [    8.752160]  put_device+0x20/0x30
> [    8.752164]  tegra_xusb_padctl_put+0x24/0x3c
> [    8.752170]  tegra_xusb_probe+0x8b0/0xd10 [xhci_tegra]
> [    8.752174]  platform_drv_probe+0x60/0xb4
> [    8.752176]  really_probe+0xf0/0x504
> [    8.752179]  driver_probe_device+0x100/0x170
> [    8.752181]  device_driver_attach+0xcc/0xd4
> [    8.752183]  __driver_attach+0xb0/0x17c
> [    8.752185]  bus_for_each_dev+0x7c/0xd4
> [    8.752187]  driver_attach+0x30/0x3c
> [    8.752189]  bus_add_driver+0x154/0x250
> [    8.752191]  driver_register+0x84/0x140
> [    8.752193]  __platform_driver_register+0x54/0x60
> [    8.752197]  tegra_xusb_init+0x40/0x1000 [xhci_tegra]
> [    8.752201]  do_one_initcall+0x54/0x2d0
> [    8.752205]  do_init_module+0x68/0x29c
> [    8.752207]  load_module+0x2178/0x26c0
> [    8.752209]  __do_sys_finit_module+0xb0/0x120
> [    8.752211]  __arm64_sys_finit_module+0x2c/0x40
> [    8.752215]  el0_svc_common.constprop.0+0x80/0x240
> [    8.752218]  do_el0_svc+0x30/0xa0
> [    8.752220]  el0_svc+0x18/0x50
> [    8.752223]  el0_sync_handler+0x90/0x318
> [    8.752225]  el0_sync+0x158/0x180
> [    8.752230] Code: a9bd7bfd 910003fd a90153f3 aa0003f3 (3940f000)
> [    8.752232] ---[ end trace 90f6c89d62d85ff5 ]---
> 
> Reset the pointer on probe failure fixes the issue.
> 
> Fixes: 53d2a715c2403 ("phy: Add Tegra XUSB pad controller support")
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
>  drivers/phy/tegra/xusb.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/phy/tegra/xusb.c b/drivers/phy/tegra/xusb.c
> index de4a46fe1763..ad88d74c1884 100644
> --- a/drivers/phy/tegra/xusb.c
> +++ b/drivers/phy/tegra/xusb.c
> @@ -1242,6 +1242,7 @@ static int tegra_xusb_padctl_probe(struct platform_device *pdev)
>  reset:
>  	reset_control_assert(padctl->rst);
>  remove:
> +	platform_set_drvdata(pdev, NULL);
>  	soc->ops->remove(padctl);
>  	return err;
>  }

Sorry, I had missed this before. Why is this necessary? The driver core
already does dev_set_drvdata(dev, NULL) on failure, which is the same as
your platform_set_drvdata() here.

I suppose one possible explanation would be if for some reason we end up
here in the error cleanup path but with err == 0.

Do you have more information on when this happens so that I can repro
and investigate? Alternatively, if you've still got this set up, can you
do a quick test to see if "err" is indeed a negative error code when we
get here?

Thierry

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