Date:   Wed, 15 Dec 2021 13:29:12 +0100
From:   Jens Wiklander <jens.wiklander@linaro.org>
To:     Xiaolei Wang <xiaolei.wang@windriver.com>
Cc:     sumit.garg@linaro.org, op-tee@lists.trustedfirmware.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] optee: Suppress false positive kmemleak report in
 optee_handle_rpc()
Message-ID: <20211215122912.GA1874103@jade>
References: <20211206120533.602062-1-xiaolei.wang@windriver.com>
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On Mon, Dec 06, 2021 at 08:05:33PM +0800, Xiaolei Wang wrote:
> We observed the following kmemleak report:
> unreferenced object 0xffff000007904500 (size 128):
>   comm "swapper/0", pid 1, jiffies 4294892671 (age 44.036s)
>   hex dump (first 32 bytes):
>     00 47 90 07 00 00 ff ff 60 00 c0 ff 00 00 00 00  .G......`.......
>     60 00 80 13 00 80 ff ff a0 00 00 00 00 00 00 00  `...............
>   backtrace:
>     [<000000004c12b1c7>] kmem_cache_alloc+0x1ac/0x2f4
>     [<000000005d23eb4f>] tee_shm_alloc+0x78/0x230
>     [<00000000794dd22c>] optee_handle_rpc+0x60/0x6f0
>     [<00000000d9f7c52d>] optee_do_call_with_arg+0x17c/0x1dc
>     [<00000000c35884da>] optee_open_session+0x128/0x1ec
>     [<000000001748f2ff>] tee_client_open_session+0x28/0x40
>     [<00000000aecb5389>] optee_enumerate_devices+0x84/0x2a0
>     [<000000003df18bf1>] optee_probe+0x674/0x6cc
>     [<000000003a4a534a>] platform_drv_probe+0x54/0xb0
>     [<000000000c51ce7d>] really_probe+0xe4/0x4d0
>     [<000000002f04c865>] driver_probe_device+0x58/0xc0
>     [<00000000b485397d>] device_driver_attach+0xc0/0xd0
>     [<00000000c835f0df>] __driver_attach+0x84/0x124
>     [<000000008e5a429c>] bus_for_each_dev+0x70/0xc0
>     [<000000001735e8a8>] driver_attach+0x24/0x30
>     [<000000006d94b04f>] bus_add_driver+0x104/0x1ec
> 
> This is not a memory leak because we pass the share memory pointer
> to secure world and would get it from secure world before releasing it.
> 
> Signed-off-by: Xiaolei Wang <xiaolei.wang@windriver.com>
> ---
>  drivers/tee/optee/smc_abi.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/tee/optee/smc_abi.c b/drivers/tee/optee/smc_abi.c
> index 6196d7c3888f..cf2e3293567d 100644
> --- a/drivers/tee/optee/smc_abi.c
> +++ b/drivers/tee/optee/smc_abi.c
> @@ -23,6 +23,7 @@
>  #include "optee_private.h"
>  #include "optee_smc.h"
>  #include "optee_rpc_cmd.h"
> +#include <linux/kmemleak.h>
>  #define CREATE_TRACE_POINTS
>  #include "optee_trace.h"
>  
> @@ -783,6 +784,7 @@ static void optee_handle_rpc(struct tee_context *ctx,
>  			param->a4 = 0;
>  			param->a5 = 0;
>  		}
> +		kmemleak_not_leak(shm);

Eventually this pointer will be freed below with the call to tee_shm_free().
I assume than once the memory is freed it's not execused from being a leak
any longer. Is that correct?

Thanks,
Jens

>  		break;
>  	case OPTEE_SMC_RPC_FUNC_FREE:
>  		shm = reg_pair_to_ptr(param->a1, param->a2);
> -- 
> 2.25.1
>