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Subject: Re: [PATCH] PCI: fix using __initdata memory after free in
 disable_acs_redir parameter
To:     Logan Gunthorpe <logang@deltatee.com>, linux-pci@vger.kernel.org,
        linux-kernel@vger.kernel.org, Bjorn Helgaas <bhelgaas@google.com>
Cc:     Stephen Bates <sbates@raithlin.com>
References: <20190115173203.14850-1-logang@deltatee.com>
From:   Jarkko Nikula <jarkko.nikula@linux.intel.com>
Message-ID: <48a93172-25a2-d6a6-e908-7d27249f1bc2@linux.intel.com>
Date:   Wed, 16 Jan 2019 11:37:46 +0200
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Hi

On 1/15/19 7:32 PM, Logan Gunthorpe wrote:
> The disable_acs_redir parameter stores a pointer to the string passed to
> pci_setup(). However, the string passed to PCI setup is actually a
> temporary copy allocated in static __initdata memory. After init, once
> the memory is freed, it is no longer valid to reference this pointer.
> 
> This bug was noticed in v5.0-rc1 after a change in commit c5eb1190074c
> ("PCI / PM: Allow runtime PM without callback functions") caused
> pci_disable_acs_redir() to be called during shutdown which manifested
> as an unable to handle kernel paging request at:
> 
> RIP: 0010:pci_enable_acs+0x3f/0x1e0
> Call Trace:
>     pci_restore_state.part.44+0x159/0x3c0
>     pci_restore_standard_config+0x33/0x40
>     pci_pm_runtime_resume+0x2b/0xd0
>     ? pci_restore_standard_config+0x40/0x40
>     __rpm_callback+0xbc/0x1b0
>     rpm_callback+0x1f/0x70
>     ? pci_restore_standard_config+0x40/0x40
>      rpm_resume+0x4f9/0x710
>     ? pci_conf1_read+0xb6/0xf0
>     ? pci_conf1_write+0xb2/0xe0
>     __pm_runtime_resume+0x47/0x70
>     pci_device_shutdown+0x1e/0x60

So this doesn't happen if you revert c5eb1190074c?

I guess this is due dev->state_saved being true set by 
pci_pm_runtime_suspend() -> pci_save_state() after my patch and now 
pci_pm_runtime_resume() -> pci_restore_standard_config() -> 
pci_restore_state() reach the pci_enable_acs(). I think this is possible 
to trigger also before my patch if device has the runtime PM callback 
defined?

> It was also likely possible to trigger this bug when hotplugging PCI
> devices.
> 
> To fix this, instead of storing a pointer, we use kstrdup to copy the
> disable_acs_redir_param to its own buffer which will never be freed.
> 
I wasn't able to trigger this but I saw
"PCI: Can't parse disable_acs_redir parameter: " followed by a few lines 
of junk during boot when I defined pci=disable_acs_redir=0000:00:xy.z 
which disappear after your patch.

Tested-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Reviewed-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>