[PATCH v3] drm/amdgpu: Fix potential out-of-bounds access in 'amdgpu_discovery_reg_base_init()'

[Srinivasan Shanmugam]

The issue arises when the array 'adev->vcn.vcn_config' is accessed
before checking if the index 'adev->vcn.num_vcn_inst' is within the
bounds of the array.

The fix involves moving the bounds check before the array access. This
ensures that 'adev->vcn.num_vcn_inst' is within the bounds of the array
before it is used as an index.

Fixes the below:
drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c:1289 
amdgpu_discovery_reg_base_init() error: testing array offset 
'adev->vcn.num_vcn_inst' after use.

Fixes: aaf1090a6cb6 ("drm/amdgpu: Add instance mask for VCN and JPEG")
Cc: Christian König <christian.koe...@amd.com>
Cc: Alex Deucher <alexander.deuc...@amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmu...@amd.com>
---
v3:
 - Added fixes tag. 

 drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c 
b/drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c
index ef800590c1ab..93c84a1c1d3e 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c
@@ -1282,11 +1282,10 @@ static int amdgpu_discovery_reg_base_init(struct 
amdgpu_device *adev)
                                 *     0b10 : encode is disabled
                                 *     0b01 : decode is disabled
                                 */
-                               adev->vcn.vcn_config[adev->vcn.num_vcn_inst] =
-                                       ip->revision & 0xc0;
-                               ip->revision &= ~0xc0;
                                if (adev->vcn.num_vcn_inst <
                                    AMDGPU_MAX_VCN_INSTANCES) {
+                                       
adev->vcn.vcn_config[adev->vcn.num_vcn_inst] =
+                                               ip->revision & 0xc0;
                                        adev->vcn.num_vcn_inst++;
                                        adev->vcn.inst_mask |=
                                                (1U << ip->instance_number);
@@ -1297,6 +1296,7 @@ static int amdgpu_discovery_reg_base_init(struct 
amdgpu_device *adev)
                                                adev->vcn.num_vcn_inst + 1,
                                                AMDGPU_MAX_VCN_INSTANCES);
                                }
+                               ip->revision &= ~0xc0;
                        }
                        if (le16_to_cpu(ip->hw_id) == SDMA0_HWID ||
                            le16_to_cpu(ip->hw_id) == SDMA1_HWID ||
-- 
2.34.1