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

[David Arcari <darcari@redhat.com>]

Hi,

On 8/25/25 1:45 PM, David Arcari wrote:
> 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@linux.intel.com>
> Cc: linux-kernel@vger.kernel.org
> Cc: Jerry Hoemann <jerry.hoemann@hpe.com>
> Signed-off-by: David Arcari <darcari@redhat.com>
> ---
>   drivers/hwtracing/intel_th/core.c | 17 +++++++++++------
>   1 file changed, 11 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/hwtracing/intel_th/core.c b/drivers/hwtracing/intel_th/core.c
> index 47d9e6c3bac0..c6f6153fcc88 100644
> --- a/drivers/hwtracing/intel_th/core.c
> +++ b/drivers/hwtracing/intel_th/core.c
> @@ -715,7 +715,9 @@ intel_th_subdevice_alloc(struct intel_th *th,
>   int intel_th_output_enable(struct intel_th *th, unsigned int otype)
>   {
>   	struct intel_th_device *thdev;
> -	int src = 0, dst = 0;
> +	int src = 0, dst = 0, ret = 0;
> +
> +	disable_irq(th->irq);
>   
>   	for (src = 0, dst = 0; dst <= th->num_thdevs; src++, dst++) {
>   		for (; src < ARRAY_SIZE(intel_th_subdevices); src++) {
> @@ -730,7 +732,7 @@ int intel_th_output_enable(struct intel_th *th, unsigned int otype)
>   
>   		/* no unallocated matching subdevices */
>   		if (src == ARRAY_SIZE(intel_th_subdevices))
> -			return -ENODEV;
> +			goto nodev;
>   
>   		for (; dst < th->num_thdevs; dst++) {
>   			if (th->thdev[dst]->type != INTEL_TH_OUTPUT)
> @@ -750,16 +752,19 @@ int intel_th_output_enable(struct intel_th *th, unsigned int otype)
>   			goto found;
>   	}
>   
> +nodev:
> +	enable_irq(th->irq);
>   	return -ENODEV;
>   
>   found:
>   	thdev = intel_th_subdevice_alloc(th, &intel_th_subdevices[src]);
>   	if (IS_ERR(thdev))
> -		return PTR_ERR(thdev);
> -
> -	th->thdev[th->num_thdevs++] = thdev;
> +		ret = PTR_ERR(thdev);
> +	else
> +		th->thdev[th->num_thdevs++] = thdev;
>   
> -	return 0;
> +	enable_irq(th->irq);
> +	return ret;
>   }
>   EXPORT_SYMBOL_GPL(intel_th_output_enable);
>   

I suspect there may be a better approach to this problem, but I did
want to add that after extensive testing this did resolve the issue.

-DA