Am 30.07.2018 um 22:14 schrieb Alex Deucher:
On Mon, Jul 30, 2018 at 5:55 AM, Michel Dänzer michel@daenzer.net wrote:
On 2018-07-24 10:53 PM, Alex Deucher wrote:
On Mon, Jul 23, 2018 at 12:32 PM, Gustavo A. R. Silva gustavo@embeddedor.com wrote:
idx can be indirectly controlled by user-space, hence leading to a potential exploitation of the Spectre variant 1 vulnerability.
This issue was detected with the help of Smatch:
drivers/gpu/drm/amd/amdgpu/amdgpu_pm.c:408 amdgpu_set_pp_force_state() warn: potential spectre issue 'data.states'
Fix this by sanitizing idx before using it to index data.states
Is this actually necessary? We already check that idx is valid a few lines before: if (ret || idx >= ARRAY_SIZE(data.states)) { count = -EINVAL; goto fail; }
A Spectre attack would be based on idx ending up too large, but the CPU speculatively executing the following code assuming idx < ARRAY_SIZE(data.states), and extracting information from the incorrectly speculated code via side channels.
I'm not sure if that's actually possible in this case, but better safe than sorry?
Yeah, I'm not sure. I guess this can't hurt.
Well is idx actually controlable by userspace in an IOCTL? I guess the answer is no.
On the other hand the array_index_nospec() macro makes the overhead absolute negligible.
So I agree that we should be better safe than sorry.
Christian.
Alex