Re: [PATCH] drm/amdgpu: Avoid possible buffer overflow

[Christophe JAILLET]

Le 21/08/2023 à 08:19, Su Hui a écrit :
smatch error:
drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c:1257 
amdgpu_discovery_reg_base_init() error:
testing array offset 'adev->vcn.num_vcn_inst' after use.
change the assignment order to avoid buffer overflow.

Fixes: c40bdfb2ffa4 ("drm/amdgpu: fix incorrect VCN revision in SRIOV")
Signed-off-by: Su Hui <su...@nfschina.com>
---
  drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c | 5 +++--
  1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c 
b/drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c
index 8e1cfc87122d..ba95526c3d45 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c
@@ -1250,11 +1250,12 @@ 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;

Hi,
I don't think that the patch is correct.

Because of the "ip->revision &= ~0xc0" which is now above it, 
"ip->revision & 0xc0" should now always be 0.

Maybe both lines should be moved within the "if"?

CJ





                                        adev->vcn.num_vcn_inst++;
                                        adev->vcn.inst_mask |=
                                                (1U << ip->instance_number);