Messages in this thread | | | Subject | Re: [PATCH] drm/amdgpu/pm: Fix potential Spectre v1 | From | Christian König <> | Date | Tue, 31 Jul 2018 08:46:10 +0200 |
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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
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