Re: [PATCH v4] drm/amd/amdgpu: Prevent null pointer dereference in GPU bandwidth calculation

[Christian König]

Am 20.01.25 um 14:38 schrieb Srinivasan Shanmugam:

If the parent is NULL, adev->pdev is used to retrieve the PCIe speed and
width, ensuring that  the function can still determine these
capabilities from the device itself.

Fixes the below:
drivers/gpu/drm/amd/amdgpu/amdgpu_device.c:6193 amdgpu_device_gpu_bandwidth()
        error: we previously assumed 'parent' could be null (see line 6180)

drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
     6170 static void amdgpu_device_gpu_bandwidth(struct amdgpu_device *adev,
     6171                                         enum pci_bus_speed *speed,
     6172                                         enum pcie_link_width *width)
     6173 {
     6174         struct pci_dev *parent = adev->pdev;
     6175
     6176         if (!speed || !width)
     6177                 return;
     6178
     6179         parent = pci_upstream_bridge(parent);
     6180         if (parent && parent->vendor == PCI_VENDOR_ID_ATI) {
                      ^^^^^^
If parent is NULL

     6181                 /* use the upstream/downstream switches internal to 
dGPU */
     6182                 *speed = pcie_get_speed_cap(parent);
     6183                 *width = pcie_get_width_cap(parent);
     6184                 while ((parent = pci_upstream_bridge(parent))) {
     6185                         if (parent->vendor == PCI_VENDOR_ID_ATI) {
     6186                                 /* use the upstream/downstream 
switches internal to dGPU */
     6187                                 *speed = pcie_get_speed_cap(parent);
     6188                                 *width = pcie_get_width_cap(parent);
     6189                         }
     6190                 }
     6191         } else {
     6192                 /* use the device itself */
--> 6193                 *speed = pcie_get_speed_cap(parent);
                                                      ^^^^^^ Then we are 
toasted here.

     6194                 *width = pcie_get_width_cap(parent);
     6195         }
     6196 }

Fixes: 9e424a5d9087 ("drm/amdgpu: cache gpu pcie link width")
Cc: Christian König <christian.koe...@amd.com>
Cc: Alex Deucher <alexander.deuc...@amd.com>
Reported-by: Dan Carpenter <dan.carpen...@linaro.org>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmu...@amd.com>
Suggested-by: Lijo Lazar <lijo.la...@amd.com>

Reviewed-by: Christian König <christian.koe...@amd.com>

---
  drivers/gpu/drm/amd/amdgpu/amdgpu_device.c | 4 ++--
  1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c 
b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
index 46af07faf8c8..ae83e23872fa 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
@@ -6187,8 +6187,8 @@ static void amdgpu_device_gpu_bandwidth(struct 
amdgpu_device *adev,
                }
        } else {
                /* use the device itself */
-               *speed = pcie_get_speed_cap(parent);
-               *width = pcie_get_width_cap(parent);
+               *speed = pcie_get_speed_cap(adev->pdev);
+               *width = pcie_get_width_cap(adev->pdev);
        }
  }