Re: [PATCH] optee: Suppress false positive kmemleak report in optee_handle_rpc()

[Sumit Garg <sumit.garg@linaro.org>]

On Fri, 10 Dec 2021 at 13:40, Jerome Forissier <jerome@forissier.org> wrote:
>
> +CC Jens, Etienne
>
> On 12/10/21 06:00, Sumit Garg wrote:
> > On Fri, 10 Dec 2021 at 09:42, Wang, Xiaolei <Xiaolei.Wang@windriver.com> wrote:
> >>
> >> -----Original Message-----
> >> From: Sumit Garg <sumit.garg@linaro.org>
> >> Sent: Thursday, December 9, 2021 7:41 PM
> >> To: Wang, Xiaolei <Xiaolei.Wang@windriver.com>
> >> Cc: jens.wiklander@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()
> >>
> >> [Please note: This e-mail is from an EXTERNAL e-mail address]
> >>
> >> On Mon, 6 Dec 2021 at 17:35, Xiaolei Wang <xiaolei.wang@windriver.com> 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.
> >>
> >>> How about if it's actually a memory leak caused by the secure world?
> >>> An example being secure world just allocates kernel memory via OPTEE_SMC_RPC_FUNC_ALLOC and doesn't free it via OPTEE_SMC_RPC_FUNC_FREE.
> >>
> >>> IMO, we need to cross-check optee-os if it's responsible for leaking kernel memory.
> >>
> >> Hi sumit,
> >>
> >> You mean we need to check whether there is a real memleak,
> >> If being secure world just allocate kernel memory via OPTEE_SMC_PRC_FUNC_ALLOC and until the end, there is no free
> >> It via OPTEE_SMC_PRC_FUNC_FREE, then we should judge it as a memory leak, wo need to judge whether it is caused by secure os?
> >
> > Yes. AFAICT, optee-os should allocate shared memory to communicate
> > with tee-supplicant. So once the communication is done, the underlying
> > shared memory should be freed. I can't think of any scenario where
> > optee-os should keep hold-off shared memory indefinitely.
>
> I believe it can happen when OP-TEE's CFG_PREALLOC_RPC_CACHE is y. See
> the config file [1] and the commit which introduced this config [2].

Okay, I see the reasoning. So during the OP-TEE driver's lifetime, the
RPC shared memory remains allocated. I guess that is done primarily
for performance reasons.

But still it doesn't feel appropriate that we term all RPC shm
allocations as not leaking memory as we might miss obvious ones.

Xiaolei,

Can you once test with CFG_PREALLOC_RPC_CACHE=n while compiling
optee-os and see if the observed memory leak disappears or not?

-Sumit

>
> [1] https://github.com/OP-TEE/optee_os/blob/3.15.0/mk/config.mk#L709
> [2] https://github.com/OP-TEE/optee_os/commit/8887663248ad
>
> --
> Jerome