Re: [PATCH] optee: Do not send requests to supplicant during shutdown

[Tyler Hicks <tyhicks@linux.microsoft.com>]

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On 2022-01-19 18:49:33, Lars Persson wrote:
> The addition of a shutdown hook by commit f25889f93184 ("optee:
> fix tee out of memory failure seen during kexec reboot") introduced a
> kernel shutdown regression that can be triggered after running the
> xtest suites.
> 
> Once the shutdown hook is called it is not possible to communicate any
> more with the supplicant process because the system is not scheduling
> task any longer. Thus if the optee driver shutdown path receives a
> supplicant RPC request from the OP-TEE we will deadlock the kernel's
> shutdown.

The system that I'm working on, and initially developed the kexec fixes
for, doesn't use a supplicant process so that would explain why I
haven't seen this issue.

What I'm a little unclear about is why the new(ish) .shutdown hook would
be the cause for this deadlock because it doesn't disable scheduling of
tasks (unless I'm forgetting something). Does disabling the shm cache
also cause tasks to no longer be scheduled? I'm having trouble finding
the documentation that describes this operation and my memory is fuzzy
since it has been a while since I've worked on OP-TEE issues.

> This unexpected event will in fact occur after the xtest suite has
> been run. It seems some cached SHM kept alive a context object which
> in turn kept alive a session towards a PTA or TA. Closing the session
> results in a socket RPC command being sent back from OP-TEE.
> 
> This sequence of events is captured by a 5.15 kernel annotated with
> extra prints:
> 
>  Calling OPTEE_SMC_DISABLE_SHM_CACHE
>  OPTEE_SMC_DISABLE_SHM_CACHE returned 0
>   freeing SHM ptr 0xFFFFFF8001079380
>  Calling OPTEE_SMC_DISABLE_SHM_CACHE
>  OPTEE_SMC_DISABLE_SHM_CACHE returned 0
>   freeing SHM ptr 0xFFFFFF8001CC5580
>  Calling OPTEE_SMC_DISABLE_SHM_CACHE
>  OPTEE_SMC_DISABLE_SHM_CACHE returned 0
>   freeing SHM ptr 0xFFFFFF8006308A80
>  Calling OPTEE_SMC_DISABLE_SHM_CACHE
>  OPTEE_SMC_DISABLE_SHM_CACHE returned 0
>   freeing SHM ptr 0xFFFFFF8006308B00
>  optee: optee_handle_rpc: a0=0XFFFF0000 a1=0XA0 a2=0X0
>  optee: optee_handle_rpc: a0=0XFFFF0005 a1=0XFFFFFF80 a2=0X61E6500
>  optee: handle_rpc_func_cmd: cmd = 0XA
>  optee_supp_thrd_req: func=0XA
> 
> Introduce a shutdown state in the optee device object to return an
> immediate error to all RPC requests in the shutdown path.
> 
> Fixes: f25889f93184 ("optee: fix tee out of memory failure seen during kexec reboot

Minor syntax error at the end of this line as it is missing the closing
double quotes and parenthesis. 

Tyler

> Signed-off-by: Lars Persson <larper@axis.com>
> ---
>  drivers/tee/optee/optee_private.h | 1 +
>  drivers/tee/optee/smc_abi.c       | 5 ++++-
>  drivers/tee/optee/supp.c          | 8 ++++++++
>  3 files changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/tee/optee/optee_private.h b/drivers/tee/optee/optee_private.h
> index 46f74ab07c7e..83380974ff44 100644
> --- a/drivers/tee/optee/optee_private.h
> +++ b/drivers/tee/optee/optee_private.h
> @@ -164,6 +164,7 @@ struct optee {
>  	bool   scan_bus_done;
>  	struct workqueue_struct *scan_bus_wq;
>  	struct work_struct scan_bus_work;
> +	bool shutting_down;
>  };
>  
>  struct optee_session {
> diff --git a/drivers/tee/optee/smc_abi.c b/drivers/tee/optee/smc_abi.c
> index 449d6a72d289..10af747da816 100644
> --- a/drivers/tee/optee/smc_abi.c
> +++ b/drivers/tee/optee/smc_abi.c
> @@ -1356,7 +1356,10 @@ static int optee_smc_remove(struct platform_device *pdev)
>   */
>  static void optee_shutdown(struct platform_device *pdev)
>  {
> -	optee_disable_shm_cache(platform_get_drvdata(pdev));
> +	struct optee *optee = platform_get_drvdata(pdev);
> +
> +	optee->shutting_down = true;
> +	optee_disable_shm_cache(optee);
>  }
>  
>  static int optee_probe(struct platform_device *pdev)
> diff --git a/drivers/tee/optee/supp.c b/drivers/tee/optee/supp.c
> index 322a543b8c27..801b4ec659e8 100644
> --- a/drivers/tee/optee/supp.c
> +++ b/drivers/tee/optee/supp.c
> @@ -83,6 +83,14 @@ u32 optee_supp_thrd_req(struct tee_context *ctx, u32 func, size_t num_params,
>  	bool interruptable;
>  	u32 ret;
>  
> +	/*
> +	 * When the system is shutting down we cannot talk
> +	 * to the supplicant anymore even if we seem to have
> +	 * an open session to it.
> +	 */
> +	if (optee->shutting_down)
> +		return TEEC_ERROR_COMMUNICATION;
> +
>  	/*
>  	 * Return in case there is no supplicant available and
>  	 * non-blocking request.
> -- 
> 2.30.2
>