On 2021-06-09 14:15:33, Jens Wiklander wrote: > Hi, > > 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: > > > > > > On 2021-06-09 09:59:04, Sumit Garg wrote: > > > > Hi Tyler, > > > > > > Hey Sumit - Thanks for the review. > > > > > > > > > > > On Wed, 9 Jun 2021 at 05:55, Tyler Hicks <tyhicks@xxxxxxxxxxxxxxxxxxx> wrote: > > > > > > > > > > Uncouple the registration of dynamic shared memory buffers from the > > > > > TEE_SHM_DMA_BUF flag. Drivers may wish to allocate dynamic shared memory > > > > > regions but do not need them to be backed by a dma-buf when the memory > > > > > region is private to the driver. > > > > > > > > In this case drivers should use tee_shm_register() instead where the > > > > memory allocated is actually private to the driver. However, you need > > > > to remove TEE_SHM_DMA_BUF as a mandatory flag for tee_shm_register(). > > > > Have a look at an example here [1]. So modifying tee_shm_alloc() for > > > > this purpose doesn't look appropriate to me. > > > > > > > > [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/security/keys/trusted-keys/trusted_tee.c#n73 > > > > > > I noticed what you did in commit 2a6ba3f794e8 ("tee: enable support to > > > register kernel memory") and considered moving ftpm and tee_bnxt_fw over > > > to tee_shm_register(). I think that's likely the right long term > > > approach but I decided against it since this series is a minimal set of > > > bug fixes that will hopefully go to stable (I'm affected by these bugs > > > in 5.4). Here are my reasons for feeling like moving to > > > tee_shm_register() isn't minimal in terms of a stable-focused fix: > > > > > > - tee_shm_alloc() looks like it should work fine with AMD-TEE today. > > > tee_shm_register() definitely does not since AMD-TEE doesn't provide a > > > .shm_register or .shm_unregister hook. This may break existing users > > > of AMD-TEE? > > > > AFAIK, ftpm and tee_bnxt_fw drivers only support OP-TEE at this point. > > See ftpm_tee_match() and optee_ctx_match() APIs in corresponding > > drivers. > > > > > - tee_shm_register() has not historically been used for kernel > > > allocations and is not fixed wrt the bug that Jens fixed in commit > > > f1bbacedb0af ("tee: don't assign shm id for private shms"). > > > > Yes, that's what I meant earlier to make the TEE_SHM_DMA_BUF flag optional. > > > > > - 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. > > > > > 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've just posted "[PATCH 0/7] tee: shared memory updates", > https://lore.kernel.org/lkml/20210609102324.2222332-1-jens.wiklander@xxxxxxxxxx/ > > Where tee_shm_alloc() is replaced by among other functions > tee_shm_alloc_kernel_buf(). tee_shm_alloc_kernel_buf() takes care of the > problem with TEE_SHM_DMA_BUF. Thanks! At first glance, that series would take care of the last three patches in my kexec/kdump series. I'm a bit worried that it is a rewrite of the shm allocator. Do you plan to send all of that to stable? (I mentioned earlier in this thread that I'm affected by these bugs in linux-5.4.y.) Also, you and Sumit don't seem to have the same opinion on kernel drivers making use of tee_shm_register() for allocations that are only used internally. Can you comment on that? I'm not clear on the next steps for fixing these kexec/kdump bugs in older releases. I appreciate any guidance here. Tyler > > Cheers, > Jens >
