[tip:timers/core] clocksource/drivers/stm32: Fix kernel panic with multiple timers

[tip-bot for Daniel Lezcano <tipbot@zytor.com>]

Commit-ID:  e0aeca3d8cbaea514eb98df1149faa918f9ec42d
Gitweb:     https://git.kernel.org/tip/e0aeca3d8cbaea514eb98df1149faa918f9ec42d
Author:     Daniel Lezcano <daniel.lezcano@linaro.org>
AuthorDate: Mon, 8 Jan 2018 14:28:50 +0100
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Mon, 8 Jan 2018 17:57:25 +0100

clocksource/drivers/stm32: Fix kernel panic with multiple timers

The current code hides a couple of bugs:

 - The global variable 'clock_event_ddata' is overwritten each time the
   init function is invoked.

This is fixed with a kmemdup() instead of assigning the global variable. That
prevents a memory corruption when several timers are defined in the DT.

 - The clockevent's event_handler is NULL if the time framework does
   not select the clockevent when registering it, this is fine but the init
   code generates in any case an interrupt leading to dereference this
   NULL pointer.

The stm32 timer works with shadow registers, a mechanism to cache the
registers. When a change is done in one buffered register, we need to
artificially generate an event to force the timer to copy the content
of the register to the shadowed register.

The auto-reload register (ARR) is one of the shadowed register as well as
the prescaler register (PSC), so in order to force the copy, we issue an
event which in turn leads to an interrupt and the NULL dereference.

This is fixed by inverting two lines where we clear the status register
before enabling the update event interrupt.

As this kernel crash is resulting from the combination of these two bugs,
the fixes are grouped into a single patch.

Tested-by: Benjamin Gaignard <benjamin.gaignard@st.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Acked-by: Benjamin Gaignard <benjamin.gaignard@st.com>
Cc: Alexandre Torgue <alexandre.torgue@st.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Maxime Coquelin <mcoquelin.stm32@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/1515418139-23276-11-git-send-email-daniel.lezcano@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 drivers/clocksource/timer-stm32.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/clocksource/timer-stm32.c b/drivers/clocksource/timer-stm32.c
index 8f24237..4bfeb99 100644
--- a/drivers/clocksource/timer-stm32.c
+++ b/drivers/clocksource/timer-stm32.c
@@ -106,6 +106,10 @@ static int __init stm32_clockevent_init(struct device_node *np)
 	unsigned long rate, max_delta;
 	int irq, ret, bits, prescaler = 1;
 
+	data = kmemdup(&clock_event_ddata, sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
 	clk = of_clk_get(np, 0);
 	if (IS_ERR(clk)) {
 		ret = PTR_ERR(clk);
@@ -156,8 +160,8 @@ static int __init stm32_clockevent_init(struct device_node *np)
 
 	writel_relaxed(prescaler - 1, data->base + TIM_PSC);
 	writel_relaxed(TIM_EGR_UG, data->base + TIM_EGR);
-	writel_relaxed(TIM_DIER_UIE, data->base + TIM_DIER);
 	writel_relaxed(0, data->base + TIM_SR);
+	writel_relaxed(TIM_DIER_UIE, data->base + TIM_DIER);
 
 	data->periodic_top = DIV_ROUND_CLOSEST(rate, prescaler * HZ);
 
@@ -184,6 +188,7 @@ err_iomap:
 err_clk_enable:
 	clk_put(clk);
 err_clk_get:
+	kfree(data);
 	return ret;
 }