drm/amdgpu/pm: Fix potential Spectre v1

commit ddf74e79a54070f277ae520722d3bab7f7a6c67a upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_pm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_pm.c
index fc818b4d849cd70a05948b457a115e09ddfe42d0..a44c3d58fef4f8952c4cdf3054b15755e75b77ef 100644 (file)
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_pm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_pm.c
@@ -31,7 +31,7 @@
 #include <linux/power_supply.h>
 #include <linux/hwmon.h>
 #include <linux/hwmon-sysfs.h>
-
+#include <linux/nospec.h>
 
 static int amdgpu_debugfs_pm_init(struct amdgpu_device *adev);
 
@@ -393,6 +393,7 @@ 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];