drm/amdgpu/pm: Fix potential Spectre v1

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

Notice that given that speculation windows are large, the policy is
to kill the speculation on the first load and not worry if it can be
completed with a dependent load/store [1].

[1] https://marc.info/?l=linux-kernel&m=152449131114778&w=2

Cc: stable@vger.kernel.org
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
CVE-2017-5753

(backported from commit ddf74e79a54070f277ae520722d3bab7f7a6c67a)
[juergh: Adjusted context.]
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_pm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_pm.c
index f8edf5483f11a65f2cade841a3ab9ea9ed8d4f4d..af456405cec35eee4b1a554479ac9a303f17dff3 100644 (file)
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_pm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_pm.c
@@ -31,6 +31,7 @@
 #include <linux/power_supply.h>
 #include <linux/hwmon.h>
 #include <linux/hwmon-sysfs.h>
+#include <linux/nospec.h>
 
 #include "amd_powerplay.h"
 
@@ -310,6 +311,7 @@ static ssize_t amdgpu_set_pp_force_state(struct device *dev,
                        count = -EINVAL;
                        goto fail;
                }
+               idx = array_index_nospec(idx, ARRAY_SIZE(data.states));
 
                amdgpu_dpm_get_pp_num_states(adev, &data);
                state = data.states[idx];