Am 30.07.2018 um 22:14 schrieb Alex Deucher:
On Mon, Jul 30, 2018 at 5:55 AM, Michel Dänzer <michel@xxxxxxxxxxx> 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@xxxxxxxxxxxxxx> 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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