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@xxxxxxxxxxxxxxxxxxx> 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-shared-buffers. > > 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: > > 1. 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). > > 2. 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@xxxxxxxxxx/ 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
