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@linux.microsoft.com 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@linux.microsoft.com 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/secu...
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-....
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've just posted "[PATCH 0/7] tee: shared memory updates", https://lore.kernel.org/lkml/20210609102324.2222332-1-jens.wiklander@linaro....
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.
Cheers, Jens