[PATCH v2] intel_th: core: fix null pointer dereference in intel_th_irq

[David Arcari]

In certain cases intel_th_irq can reference a null entry in
the th->thdev array.  This results in the splat shown below.
The problem is that intel_th_output_enable() can modify the
thdev[] array at the same time intel_th_irq is referencing
the same array.  This can be fixed by disabling interrupts
during the call to intel_th_output_enable().

BUG: kernel NULL pointer dereference, address: 0000000000000304
Oops: Oops: 0000 [#1] SMP NOPTI
RIP: 0010:intel_th_irq+0x26/0x70 [intel_th]
Call Trace:
 <IRQ>
 ? show_trace_log_lvl+0x1b0/0x2f0
 ? show_trace_log_lvl+0x1b0/0x2f0
 ? __handle_irq_event_percpu+0x4a/0x180
 ? __die_body.cold+0x8/0x12
 ? page_fault_oops+0x148/0x160
 ? exc_page_fault+0x73/0x160
 ? asm_exc_page_fault+0x26/0x30
 ? intel_th_irq+0x26/0x70 [intel_th]
 __handle_irq_event_percpu+0x4a/0x180
 handle_irq_event+0x38/0x80
handle_fasteoi_irq+0x78/0x200
__common_interrupt+0x3e/0x90
common_interrupt+0x80/0xa0
</IRQ>

Fixes: a753bfcfdb1f ("intel_th: Make the switch allocate its subdevices")
Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: Jerry Hoemann <jerry.hoemann@xxxxxxx>
Signed-off-by: David Arcari <darcari@xxxxxxxxxx>
---
v2: switched to use scoped based lock guard functionality

drivers/hwtracing/intel_th/core.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/hwtracing/intel_th/core.c b/drivers/hwtracing/intel_th/core.c
index 47d9e6c3bac0..7b7dcc651efe 100644
--- a/drivers/hwtracing/intel_th/core.c
+++ b/drivers/hwtracing/intel_th/core.c
@@ -717,6 +717,8 @@ int intel_th_output_enable(struct intel_th *th, unsigned int otype)
 	struct intel_th_device *thdev;
 	int src = 0, dst = 0;
 
+	guard(disable_irq)(&th->irq);
+
 	for (src = 0, dst = 0; dst <= th->num_thdevs; src++, dst++) {
 		for (; src < ARRAY_SIZE(intel_th_subdevices); src++) {
 			if (intel_th_subdevices[src].type != INTEL_TH_OUTPUT)
-- 
2.51.0