On Fri, 18 Oct 2019 at 12:03, Lorenzo Pieralisi
[off-list ref] wrote:

On Fri, Oct 18, 2019 at 11:51:11AM +0200, Ulf Hansson wrote:

quoted

On Fri, 18 Oct 2019 at 11:38, Lorenzo Pieralisi
[off-list ref] wrote:

quoted

On Thu, Oct 10, 2019 at 01:39:25PM +0200, Ulf Hansson wrote:

quoted

When the WFI state have been selected, the in-parameter idx to
psci_enter_idle_state() is zero. In this case, we must not index the state
array as "state[idx - 1]", as it means accessing data outside the array.
Fix the bug by pre-checking if idx is zero.

Fixes: 9ffeb6d08c3a ("PSCI: cpuidle: Refactor CPU suspend power_state parameter handling")
Signed-off-by: Ulf Hansson <redacted>
---
 drivers/cpuidle/cpuidle-psci.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/cpuidle/cpuidle-psci.c b/drivers/cpuidle/cpuidle-psci.c
index f3c1a2396f98..2e91c8d6c211 100644
--- a/drivers/cpuidle/cpuidle-psci.c
+++ b/drivers/cpuidle/cpuidle-psci.c

@@ -27,10 +27,10 @@ static DEFINE_PER_CPU_READ_MOSTLY(u32 *, psci_power_state);
 static int psci_enter_idle_state(struct cpuidle_device *dev,
                              struct cpuidle_driver *drv, int idx)
 {
-     u32 *state = __this_cpu_read(psci_power_state);
+     u32 *states = __this_cpu_read(psci_power_state);
+     u32 state = idx ? states[idx - 1] : 0;

-     return CPU_PM_CPU_IDLE_ENTER_PARAM(psci_cpu_suspend_enter,
-                                        idx, state[idx - 1]);
+     return CPU_PM_CPU_IDLE_ENTER_PARAM(psci_cpu_suspend_enter, idx, state);

Technically we don't dereference that array entry but I agree this
is ugly and potentially broken.

No sure understand the non-deference part.

If the governor selects WFI, the idx will be 0 - and thus we end up
using state[-1], doesn't that dereference an invalid address, no?

No because CPU_PM_CPU_IDLE_ENTER_PARAM is a macro, the code it
preprocesses to won't dereference state[idx - 1] if idx == 0.

I agree it is *very* ugly but technically code is not broken.

Ahh, got it, thanks!

quoted

quoted

My preference is aligning it with ACPI code and allocate one more
entry in the psci_power_state array (useless for wfi, agreed but
at least we remove this (-1) handling from the code).

I can do that, but sounds like a slightly bigger change. Are you fine
if I do that on top, so we can get this sent as fix for v5.4-rc[n]?

Technically we are not fixing anything; it is not such a big
change, we need to allocate one entry more and update the array
indexing.

Okay, let me do the change - and it seems like it doesn't even have to
be sent as a fix then. Right?

Kind regards
Uffe

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