[<prev] [next>] [<thread-prev] [day] [month] [year] [list]
Message-ID: <306e8a8b-e411-102c-3ebb-a226dcb5adc8@sangfor.com.cn>
Date: Sat, 6 May 2023 08:44:19 +0800
From: Ding Hui <dinghui@...gfor.com.cn>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: bhelgaas@...gle.com, sathyanarayanan.kuppuswamy@...ux.intel.com,
vidyas@...dia.com, david.e.box@...ux.intel.com,
kai.heng.feng@...onical.com, michael.a.bottini@...ux.intel.com,
rajatja@...gle.com, qinzongquan@...gfor.com.cn,
linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PCI/ASPM: fix UAF by disable ASPM for link when child
function is removed
On 2023/5/6 4:58, Bjorn Helgaas wrote:
> On Thu, May 04, 2023 at 08:34:18PM +0800, Ding Hui wrote:
>> If the Function 0 of a Multi-Function device is software removed,
>> a freed downstream pointer will be left in struct pcie_link_state,
>> and then when pcie_config_aspm_link() be invoked from any path,
>> we will trigger use-after-free.
>>
>> Based on the PCIe spec about ASPM Control (PCIe r6.0, sec 7.5.3.7),
>> for Multi-Function Devices (including ARI Devices), it is recommended
>> that software program the same value in all Functions. For ARI
>> Devices, ASPM Control is determined solely by the setting in Function 0.
>>
>> So we can just disable ASPM of the whole component if any child
>> function is removed, the downstream pointer will be avoided from
>> use-after-free, that will also avoid other potential corner cases.
>>
>> Fixes: b5a0a9b59c81 ("PCI/ASPM: Read and set up L1 substate capabilities")
>> Debugged-by: Zongquan Qin <qinzongquan@...gfor.com.cn>
>> Suggestion-by: Bjorn Helgaas <bhelgaas@...gle.com>
>> Signed-off-by: Ding Hui <dinghui@...gfor.com.cn>
>> ---
>> drivers/pci/pcie/aspm.c | 15 +++++++--------
>> 1 file changed, 7 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
>> index 66d7514ca111..1bf8306141aa 100644
>> --- a/drivers/pci/pcie/aspm.c
>> +++ b/drivers/pci/pcie/aspm.c
>> @@ -1010,18 +1010,17 @@ void pcie_aspm_exit_link_state(struct pci_dev *pdev)
>
> Not directly related to your patch, but this looks racy to me:
>
> void pcie_aspm_exit_link_state(struct pci_dev *pdev)
> {
> struct pci_dev *parent = pdev->bus->self;
>
> if (!parent || !parent->link_state)
> return;
>
> down_read(&pci_bus_sem);
> mutex_lock(&aspm_lock);
>
> link = parent->link_state;
> root = link->root;
> ...
> free_link_state(link);
> link->pdev->link_state = NULL;
> kfree(link);
>
> Since we check "parent->link_state" before acquiring the locks, I
> suspect that removing two functions at the same time could end up with
> a NULL pointer dereference:
>
> pcie_aspm_exit_link_state(fn 0) pcie_aspm_exit_link_state(fn 1)
> parent = X parent = X
> parent->link_state != NULL parent->link_state != NULL
>
> acquire locks
> free_link_state(link)
> link->pdev->link_state = NULL # aka parent->link_state
> kfree(link)
> release locks
>
> acquire locks
> link = parent->link_state # now NULL
> root = link->root # NULL ptr
>
> What do you think? I guess if this *is* a race, it should be fixed by
> a separate patch.
>
Maybe there's no need to worry about the race, when a pci device is removing,
the pci_rescan_remove_lock should be acquired.
Anyway, double check would be safer.
>> down_read(&pci_bus_sem);
>> mutex_lock(&aspm_lock);
>> - /*
>> - * All PCIe functions are in one slot, remove one function will remove
>> - * the whole slot, so just wait until we are the last function left.
>> - */
>> - if (!list_empty(&parent->subordinate->devices))
>> - goto out;
>>
>> link = parent->link_state;
>> root = link->root;
>> parent_link = link->parent;
>>
>> - /* All functions are removed, so just disable ASPM for the link */
>> + /*
>> + * Any function is removed (including software removing), just
>> + * disable ASPM for the link, in case we can not configure the same
>> + * setting for all functions.
>> + * See PCIe r6.0, sec 7.5.3.7.
>> + */
>> pcie_config_aspm_link(link, 0);
>> list_del(&link->sibling);
>> /* Clock PM is for endpoint device */
>> @@ -1032,7 +1031,7 @@ void pcie_aspm_exit_link_state(struct pci_dev *pdev)
>> pcie_update_aspm_capable(root);
>> pcie_config_aspm_path(parent_link);
>> }
>> -out:
>> +
>> mutex_unlock(&aspm_lock);
>> up_read(&pci_bus_sem);
>> }
>> --
>> 2.17.1
>>
>
--
Thanks,
- Ding Hui
Powered by blists - more mailing lists