On Wed, Jun 09, 2021 at 04:22:49PM +0530, Sumit Garg wrote:
- Rijo
On Wed, 9 Jun 2021 at 11:16, Tyler Hicks tyhicks@linux.microsoft.com wrote:
[snip]
- tee_shm_alloc() performs allocations using contiguous pages from alloc_pages() while tee_shm_register() performs non-contiguous allocations with kcalloc(). I suspect this would be fine but I don't know the secure world side of these things well enough to assess the risk involved with such a change on the kernel side.
I don't think that would make any difference.
Agree.
I should have mentioned this in the cover letter but my hope was that these minimal changes would be accepted and then additional work could be done to merge tee_shm_alloc() and tee_shm_register() in a way that would allow the caller to request contiguous or non-contiguous pages, fix up the additional issues mentioned above, and then adjust the call sites in ftpm and tee_bnxt_fw as appropriate.
I think that's a bigger set of changes because there are several things that still confuse/concern me:
- Why does tee_shm_alloc() use TEE_SHM_MAPPED while tee_shm_register() uses TEE_SHM_KERNEL_MAPPED or TEE_SHM_USER_MAPPED? Why do all three exist?
AFAIK, its due the the inherent nature of tee_shm_alloc() and tee_shm_register() where tee_shm_alloc() doesn't need to know whether its a kernel or user-space memory since it is the one that allocates whereas tee_shm_register() need to know that since it has to register pre-allocated client memory.
- Why does tee_shm_register() unconditionally use non-contiguous allocations without ever taking into account whether or not OPTEE_SMC_SEC_CAP_DYNAMIC_SHM was set? It sounds like that's required from my reading of https://optee.readthedocs.io/en/latest/architecture/core.html#noncontiguous-....
Yeah, but do we have platforms in OP-TEE that don't support dynamic shared memory? I guess it has become the sane default which is a mandatory requirement when it comes to OP-TEE driver in u-boot.
- Why is TEE_SHM_REGISTER implemented at the TEE driver level when it is specific to OP-TEE? How to better abstract that away?
I would like you to go through Section "3.2.4. Shared Memory" in TEE Client API Specification. There are two standard ways for shared memory approach with TEE:
- A Shared Memory block can either be existing Client Application
memory (kernel driver in our case) which is subsequently registered with the TEE Client API (using tee_shm_register() in our case).
- Or memory which is allocated on behalf of the Client Application
using the TEE Client API (using tee_shm_alloc() in our case).
Let me know if you agree with the more minimal approach that I took for these bug fix series or still feel like tee_shm_register() should be fixed up so that it is usable. Thanks!
From drivers perspective I think the change should be:
tee_shm_alloc()
to
kcalloc() tee_shm_register()
I had another approach in mind in "[PATCH 0/7] tee: shared memory updates", https://lore.kernel.org/lkml/20210609102324.2222332-1-jens.wiklander@linaro....
The flags needed by tee_shm_alloc() and tee_shm_register() aren't very intuitive and in fact only accept quite few combinations. So my idea was to hide those flags from callers outside of the TEE subsystem with tee_shm_alloc_kernel_buf().
The approach with tee_shm_register() you suggest above has the drawback that the TEE driver is forced to be able to handle any kernel memory. This is OK with OP-TEE and dynamic shared memory enabled, but there are platforms where dynamic shared memory isn't enabled. In those case must the memory be allocated from a special pool.
Do you see any problem with instead replacing tee_shm_alloc() with tee_shm_alloc_kernel_buf()?
Cheers, Jens