On Fri, Dec 10, 2021 at 03:08:21PM +0530, Sumit Garg wrote:
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()
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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.
IIUC this patch adds kmemleak_not_leak() at (pretty much) the last possible point before *ownership* of the SHM block is passed from kernel to OP-TEE.
Sure, after we change ownership it could still be leaked... but it can no longer be leaked by the kernel because the kernel no longer owns it! More importantly, it makes no sense to run the kernel memory detector on the buffer because it simply can't work.
After the RPC completes, doesn't it become impossible for kmemleak to scan to see if the pointer is lost[1]? kmemleak is essentially a tracing garbage collector and needs to be able to scan all memory that could hold a pointer to leakable memory. After the RPC completes the only copy of the pointer will be stored in a memory region that the kernel is prohibited from reading. How could kmemleak possibly give you a useful answer in this circumstance?
In other words if there's nothing kmemleak could do to fix this situation then marking the memory as kmemleak_not_leak() seems entirely appropriate (although it should be prefaced with a big comment explaining the change of ownerhship and why kmemleak cannot work).
Daniel.
[1] Everything I've said here hinges on this being true... so if I've made a mistake about where OP-TEE stores this pointer then most of the rest of this post is junk ;-)