From: Jens Wiklander <firstname.lastname@example.org>
To: Sumit Garg <email@example.com>
Cc: "Tyler Hicks" <firstname.lastname@example.org>,
"Allen Pais" <email@example.com>,
"Peter Huewe" <firstname.lastname@example.org>,
"Jarkko Sakkinen" <email@example.com>,
"Jason Gunthorpe" <firstname.lastname@example.org>,
"Vikas Gupta" <email@example.com>,
"Thirupathaiah Annapureddy" <firstname.lastname@example.org>,
"Pavel Tatashin" <email@example.com>,
"Rafał Miłecki" <firstname.lastname@example.org>,
"Linux Kernel Mailing List" <email@example.com>
Subject: Re: [PATCH v3 5/7] tee: Support shm registration without dma-buf backing
Date: Thu, 10 Jun 2021 09:18:12 +0200 [thread overview]
Message-ID: <20210610071812.GA2753553@jade> (raw)
On Wed, Jun 09, 2021 at 04:22:49PM +0530, Sumit Garg wrote:
> + Rijo
> On Wed, 9 Jun 2021 at 11:16, Tyler Hicks <firstname.lastname@example.org> wrote:
> > - 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:
I had another approach in mind in "[PATCH 0/7] tee: shared memory updates",
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
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()
next prev parent reply other threads:[~2021-06-10 7:19 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-09 0:23 [PATCH v3 0/7] tee: Improve support for kexec and kdump Tyler Hicks
2021-06-09 0:23 ` [PATCH v3 1/7] optee: Fix memory leak when failing to register shm pages Tyler Hicks
2021-06-09 0:23 ` [PATCH v3 2/7] optee: Refuse to load the driver under the kdump kernel Tyler Hicks
2021-06-09 0:23 ` [PATCH v3 3/7] optee: fix tee out of memory failure seen during kexec reboot Tyler Hicks
2021-06-09 0:23 ` [PATCH v3 4/7] optee: Clear stale cache entries during initialization Tyler Hicks
2021-06-09 0:23 ` [PATCH v3 5/7] tee: Support shm registration without dma-buf backing Tyler Hicks
2021-06-09 4:29 ` Sumit Garg
2021-06-09 5:46 ` Tyler Hicks
2021-06-09 10:52 ` Sumit Garg
2021-06-09 12:15 ` Jens Wiklander
2021-06-09 13:42 ` Tyler Hicks
2021-06-09 13:51 ` Tyler Hicks
2021-06-10 7:34 ` Jens Wiklander
2021-06-10 21:00 ` Tyler Hicks
2021-06-10 7:49 ` Jens Wiklander
2021-06-10 21:05 ` Tyler Hicks
2021-06-10 7:40 ` Allen Pais
2021-06-10 7:18 ` Jens Wiklander [this message]
2021-06-10 12:14 ` Sumit Garg
2021-06-09 0:23 ` [PATCH v3 6/7] tpm_ftpm_tee: Free and unregister dynamic shared memory during kexec Tyler Hicks
2021-06-09 0:23 ` [PATCH v3 7/7] firmware: tee_bnxt: Release shm, session, and context " Tyler Hicks
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