Re: [PATCH v2] PCI: designware-ep: Fix the reference to pci->num_{ib,ob}_windows before setting

[Kunihiko Hayashi]

Cc: Hou Zhiqiang <Zhiqiang.Hou@xxxxxxx>

I found that this patch would cause null pointer dereference exception
when removing the function link.

If once linking the test function to the controller,
  # ln -s functions/pci_epf_test/test controllers/66000000.pcie-ep/

and unlinking it immediately,
  # rm controllers/66000000.pcie-ep/test

then the driver will occur null pointer access in dw_pcie_ep_clear_bar()
because ep->ib_window_map doesn't have a pointer to allocated memory yet.

To fix the original issue, I strongly recommend to apply Hou's patch [1]
instead of this patch.

Thank you,

[1] https://patchwork.kernel.org/project/linux-pci/patch/20210125044803.4310-1-Zhiqiang.Hou@xxxxxxx/

On 2021/01/21 0:20, Rob Herring wrote:
> On Mon, Jan 18, 2021 at 5:10 PM Kunihiko Hayashi
> <hayashi.kunihiko@xxxxxxxxxxxxx> wrote:
> > The commit 281f1f99cf3a ("PCI: dwc: Detect number of iATU windows") gets
> > the values of pci->num_ib_windows and pci->num_ob_windows from iATU
> > registers instead of DT properties in dw_pcie_iatu_detect_regions*() or its
> > unroll version.
> >
> > However, before the values are set, the allocations in dw_pcie_ep_init()
> > refer them to determine the sizes of window_map. As a result, null pointer
> > dereference exception will occur when linking the EP function and the
> > controller.
> >
> >    # ln -s functions/pci_epf_test/test controllers/66000000.pcie-ep/
> >    Unable to handle kernel NULL pointer dereference at virtual address
> >    0000000000000010
> >
> > The call trace is as follows:
> >
> >    Call trace:
> >     _find_next_bit.constprop.1+0xc/0x88
> >     dw_pcie_ep_set_bar+0x78/0x1f8
> >     pci_epc_set_bar+0x9c/0xe8
> >     pci_epf_test_core_init+0xe8/0x220
> >     pci_epf_test_bind+0x1e0/0x378
> >     pci_epf_bind+0x54/0xb0
> >     pci_epc_epf_link+0x58/0x80
> >     configfs_symlink+0x1c0/0x570
> >     vfs_symlink+0xdc/0x198
> >     do_symlinkat+0xa0/0x110
> >     __arm64_sys_symlinkat+0x28/0x38
> >     el0_svc_common+0x84/0x1a0
> >     do_el0_svc+0x38/0x88
> >     el0_svc+0x1c/0x28
> >     el0_sync_handler+0x88/0xb0
> >     el0_sync+0x140/0x180
> >
> > The pci->num_{ib,ob}_windows should be referenced after they are set by
> > dw_pcie_iatu_detect_regions*() called from dw_pcie_setup().
> >
> > Cc: Rob Herring <robh@xxxxxxxxxx>
> > Fixes: 281f1f99cf3a ("PCI: dwc: Detect number of iATU windows")
> > Signed-off-by: Kunihiko Hayashi <hayashi.kunihiko@xxxxxxxxxxxxx>
> > ---
> >   drivers/pci/controller/dwc/pcie-designware-ep.c | 41 ++++++++++++-------------
> >   1 file changed, 20 insertions(+), 21 deletions(-)
>
> Reviewed-by: Rob Herring <robh@xxxxxxxxxx>

--
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Best Regards
Kunihiko Hayashi