[Linaro-mm-sig] Re: [PATCH v10 5/9] tee: new ioctl to a register tee_shm from a dmabuf file descriptor

On Tue, Jun 17, 2025 at 12:48 PM Sumit Garg sumit.garg@kernel.org wrote:

On Tue, Jun 10, 2025 at 03:13:49PM +0200, Jens Wiklander wrote:

...

From: Etienne Carriere etienne.carriere@foss.st.com

Add a userspace API to create a tee_shm object that refers to a dmabuf reference.

Userspace registers the dmabuf file descriptor as in a tee_shm object. The registration is completed with a tee_shm returned file descriptor.

Userspace is free to close the dmabuf file descriptor after it has been registered since all the resources are now held via the new tee_shm object.

Closing the tee_shm file descriptor will eventually release all resources used by the tee_shm object when all references are released.

The new IOCTL, TEE_IOC_SHM_REGISTER_FD, supports dmabuf references to physically contiguous memory buffers. Dmabuf references acquired from the TEE DMA-heap can be used as protected memory for Secure Video Path and such use cases. It depends on the TEE and the TEE driver if dmabuf references acquired by other means can be used.

A new tee_shm flag is added to identify tee_shm objects built from a registered dmabuf, TEE_SHM_DMA_BUF.

Signed-off-by: Etienne Carriere etienne.carriere@foss.st.com Signed-off-by: Olivier Masse olivier.masse@nxp.com Signed-off-by: Jens Wiklander jens.wiklander@linaro.org

---

drivers/tee/tee_core.c | 63 +++++++++++++++++++++- drivers/tee/tee_private.h | 10 ++++ drivers/tee/tee_shm.c | 106 ++++++++++++++++++++++++++++++++++++-- include/linux/tee_core.h | 1 + include/linux/tee_drv.h | 10 ++++ include/uapi/linux/tee.h | 31 +++++++++++ 6 files changed, 217 insertions(+), 4 deletions(-)

diff --git a/drivers/tee/tee_core.c b/drivers/tee/tee_core.c index 5259b8223c27..0e9d9e5872a4 100644 --- a/drivers/tee/tee_core.c +++ b/drivers/tee/tee_core.c @@ -353,11 +353,49 @@ tee_ioctl_shm_register(struct tee_context *ctx, return ret; }

+static int +tee_ioctl_shm_register_fd(struct tee_context *ctx,

•                   struct tee_ioctl_shm_register_fd_data __user *udata)
  

+{

• struct tee_ioctl_shm_register_fd_data data;
  

• struct tee_shm *shm;
  

• long ret;
  

• if (copy_from_user(&data, udata, sizeof(data)))
  

•         return -EFAULT;
  

• /* Currently no input flags are supported */
  

• if (data.flags)
  

•         return -EINVAL;
  

• shm = tee_shm_register_fd(ctx, data.fd);
  

• if (IS_ERR(shm))
  

•         return -EINVAL;
  

• data.id = shm->id;
  

• data.flags = shm->flags;
  

• data.size = shm->size;
  

• if (copy_to_user(udata, &data, sizeof(data)))
  

•         ret = -EFAULT;
  

• else
  

•         ret = tee_shm_get_fd(shm);
  

• /*
  

•  * When user space closes the file descriptor the shared memory
  

•  * should be freed or if tee_shm_get_fd() failed then it will
  

•  * be freed immediately.
  

•  */
  

• tee_shm_put(shm);
  

• return ret;
  

+}

static int param_from_user_memref(struct tee_context *ctx, struct tee_param_memref *memref, struct tee_ioctl_param *ip) { struct tee_shm *shm;

• size_t offs = 0;
  
  /*
   * If a NULL pointer is passed to a TA in the TEE,
  

@@ -388,6 +426,26 @@ static int param_from_user_memref(struct tee_context *ctx, tee_shm_put(shm); return -EINVAL; }

•         if (shm->flags & TEE_SHM_DMA_BUF) {
  

•                 struct tee_shm_dmabuf_ref *ref;
  

•                 ref = container_of(shm, struct tee_shm_dmabuf_ref, shm);
  

•                 if (ref->parent_shm) {
  

•                         /*
  

•                          * The shm already has one reference to
  

•                          * ref->parent_shm so we are clear of 0.
  

•                          * We're getting another reference since
  

•                          * this shm will be used in the parameter
  

•                          * list instead of the shm we got with
  

•                          * tee_shm_get_from_id() above.
  

•                          */
  

•                         refcount_inc(&ref->parent_shm->refcount);
  

•                         tee_shm_put(shm);
  

•                         shm = ref->parent_shm;
  

•                         offs = ref->offset;
  

•                 }
  

•         }
  } else if (ctx->cap_memref_null) {
          /* Pass NULL pointer to OP-TEE */
          shm = NULL;
  

@@ -395,7 +453,7 @@ static int param_from_user_memref(struct tee_context *ctx, return -EINVAL; }

• memref->shm_offs = ip->a;
  

• memref->shm_offs = ip->a + offs;
  memref->size = ip->b;
  memref->shm = shm;
  
  

@@ -841,6 +899,8 @@ static long tee_ioctl(struct file *filp, unsigned int cmd, unsigned long arg) return tee_ioctl_shm_alloc(ctx, uarg); case TEE_IOC_SHM_REGISTER: return tee_ioctl_shm_register(ctx, uarg);

• case TEE_IOC_SHM_REGISTER_FD:
  

•         return tee_ioctl_shm_register_fd(ctx, uarg);
  case TEE_IOC_OPEN_SESSION:
          return tee_ioctl_open_session(ctx, uarg);
  case TEE_IOC_INVOKE:
  

@@ -1300,3 +1360,4 @@ MODULE_AUTHOR("Linaro"); MODULE_DESCRIPTION("TEE Driver"); MODULE_VERSION("1.0"); MODULE_LICENSE("GPL v2"); +MODULE_IMPORT_NS("DMA_BUF"); diff --git a/drivers/tee/tee_private.h b/drivers/tee/tee_private.h index 6c6ff5d5eed2..308467705da6 100644 --- a/drivers/tee/tee_private.h +++ b/drivers/tee/tee_private.h @@ -13,6 +13,16 @@ #include <linux/mutex.h> #include <linux/types.h>

+/* extra references appended to shm object for registered shared memory */ +struct tee_shm_dmabuf_ref {

• struct tee_shm shm;
  

• size_t offset;
  

• struct dma_buf *dmabuf;
  

• struct dma_buf_attachment *attach;
  

• struct sg_table *sgt;
  

• struct tee_shm *parent_shm;
  

+};

int tee_shm_get_fd(struct tee_shm *shm);

bool tee_device_get(struct tee_device *teedev); diff --git a/drivers/tee/tee_shm.c b/drivers/tee/tee_shm.c index daf6e5cfd59a..e63095e84644 100644 --- a/drivers/tee/tee_shm.c +++ b/drivers/tee/tee_shm.c @@ -4,6 +4,7 @@ */ #include <linux/anon_inodes.h> #include <linux/device.h> +#include <linux/dma-buf.h> #include <linux/idr.h> #include <linux/io.h> #include <linux/mm.h> @@ -45,7 +46,21 @@ static void release_registered_pages(struct tee_shm *shm)

static void tee_shm_release(struct tee_device *teedev, struct tee_shm *shm) {

• if (shm->flags & TEE_SHM_POOL) {
  

• void *p = shm;
  

• if (shm->flags & TEE_SHM_DMA_BUF) {
  

•         struct tee_shm_dmabuf_ref *ref;
  

•         ref = container_of(shm, struct tee_shm_dmabuf_ref, shm);
  

•         p = ref;
  

•         if (ref->attach) {
  

•                 dma_buf_unmap_attachment(ref->attach, ref->sgt,
  

•                                          DMA_BIDIRECTIONAL);
  

•                 dma_buf_detach(ref->dmabuf, ref->attach);
  

•         }
  

•         dma_buf_put(ref->dmabuf);
  

• } else if (shm->flags & TEE_SHM_POOL) {
          teedev->pool->ops->free(teedev->pool, shm);
  } else if (shm->flags & TEE_SHM_DYNAMIC) {
          int rc = teedev->desc->ops->shm_unregister(shm->ctx, shm);
  

@@ -59,7 +74,7 @@ static void tee_shm_release(struct tee_device *teedev, struct tee_shm *shm)

  teedev_ctx_put(shm->ctx);

• kfree(shm);
  

• kfree(p);
  
  tee_device_put(teedev);
  

} @@ -169,7 +184,7 @@ struct tee_shm *tee_shm_alloc_user_buf(struct tee_context *ctx, size_t size)

• tee_client_invoke_func(). The memory allocated is later freed with a
• call to tee_shm_free().

• • @returns a pointer to 'struct tee_shm'

• • @returns a pointer to 'struct tee_shm' on success, and ERR_PTR on failure
  */

struct tee_shm *tee_shm_alloc_kernel_buf(struct tee_context *ctx, size_t size) { @@ -179,6 +194,91 @@ struct tee_shm *tee_shm_alloc_kernel_buf(struct tee_context *ctx, size_t size) } EXPORT_SYMBOL_GPL(tee_shm_alloc_kernel_buf);

+struct tee_shm *tee_shm_register_fd(struct tee_context *ctx, int fd) +{

• struct tee_shm_dmabuf_ref *ref;
  

• int rc;
  

• if (!tee_device_get(ctx->teedev))
  

•         return ERR_PTR(-EINVAL);
  

• teedev_ctx_get(ctx);
  

• ref = kzalloc(sizeof(*ref), GFP_KERNEL);
  

• if (!ref) {
  

•         rc = -ENOMEM;
  

•         goto err_put_tee;
  

• }
  

• refcount_set(&ref->shm.refcount, 1);
  

• ref->shm.ctx = ctx;
  

• ref->shm.id = -1;
  

• ref->shm.flags = TEE_SHM_DMA_BUF;
  

• ref->dmabuf = dma_buf_get(fd);
  

• if (IS_ERR(ref->dmabuf)) {
  

•         rc = PTR_ERR(ref->dmabuf);
  

•         goto err_kfree_ref;
  

• }
  

• rc = tee_heap_update_from_dma_buf(ctx->teedev, ref->dmabuf,
  

•                                   &ref->offset, &ref->shm,
  

•                                   &ref->parent_shm);
  

• if (!rc)
  

•         goto out;
  

One odd thing I find here, why do we bail out on success case here? Don't we need the DMA buffer attach and map APIs to be invoked on success case here?

No, because if tee_heap_update_from_dma_buf() succeeds, we know everything we need about the buffer. Note that we're returning a valid pointer below to indicate success.

Cheers, Jens

-Sumit

...

• if (rc != -EINVAL)
  

•         goto err_put_dmabuf;
  

• ref->attach = dma_buf_attach(ref->dmabuf, &ctx->teedev->dev);
  

• if (IS_ERR(ref->attach)) {
  

•         rc = PTR_ERR(ref->attach);
  

•         goto err_put_dmabuf;
  

• }
  

• ref->sgt = dma_buf_map_attachment(ref->attach, DMA_BIDIRECTIONAL);
  

• if (IS_ERR(ref->sgt)) {
  

•         rc = PTR_ERR(ref->sgt);
  

•         goto err_detach;
  

• }
  

• if (sg_nents(ref->sgt->sgl) != 1) {
  

•         rc = -EINVAL;
  

•         goto err_unmap_attachement;
  

• }
  

• ref->shm.paddr = page_to_phys(sg_page(ref->sgt->sgl));
  

• ref->shm.size = ref->sgt->sgl->length;
  

+out:

• mutex_lock(&ref->shm.ctx->teedev->mutex);
  

• ref->shm.id = idr_alloc(&ref->shm.ctx->teedev->idr, &ref->shm,
  

•                         1, 0, GFP_KERNEL);
  

• mutex_unlock(&ref->shm.ctx->teedev->mutex);
  

• if (ref->shm.id < 0) {
  

•         rc = ref->shm.id;
  

•         if (ref->attach)
  

•                 goto err_unmap_attachement;
  

•         goto err_put_dmabuf;
  

• }
  

• return &ref->shm;
  

+err_unmap_attachement:

• dma_buf_unmap_attachment(ref->attach, ref->sgt, DMA_BIDIRECTIONAL);
  

+err_detach:

• dma_buf_detach(ref->dmabuf, ref->attach);
  

+err_put_dmabuf:

• dma_buf_put(ref->dmabuf);
  

+err_kfree_ref:

• kfree(ref);
  

+err_put_tee:

• teedev_ctx_put(ctx);
  

• tee_device_put(ctx->teedev);
  

• return ERR_PTR(rc);
  

+} +EXPORT_SYMBOL_GPL(tee_shm_register_fd);

/**

• tee_shm_alloc_priv_buf() - Allocate shared memory for a privately shared

•                     kernel buffer
  

diff --git a/include/linux/tee_core.h b/include/linux/tee_core.h index 22e03d897dc3..f17710196c4c 100644 --- a/include/linux/tee_core.h +++ b/include/linux/tee_core.h @@ -28,6 +28,7 @@ #define TEE_SHM_USER_MAPPED BIT(1) /* Memory mapped in user space */ #define TEE_SHM_POOL BIT(2) /* Memory allocated from pool */ #define TEE_SHM_PRIV BIT(3) /* Memory private to TEE driver */ +#define TEE_SHM_DMA_BUF BIT(4) /* Memory with dma-buf handle */

#define TEE_DEVICE_FLAG_REGISTERED 0x1 #define TEE_MAX_DEV_NAME_LEN 32 diff --git a/include/linux/tee_drv.h b/include/linux/tee_drv.h index a54c203000ed..824f1251de60 100644 --- a/include/linux/tee_drv.h +++ b/include/linux/tee_drv.h @@ -116,6 +116,16 @@ struct tee_shm *tee_shm_alloc_kernel_buf(struct tee_context *ctx, size_t size); struct tee_shm *tee_shm_register_kernel_buf(struct tee_context *ctx, void *addr, size_t length);

+/**

• • tee_shm_register_fd() - Register shared memory from file descriptor
• • @ctx: Context that allocates the shared memory
• • @fd: Shared memory file descriptor reference
• • @returns a pointer to 'struct tee_shm' on success, and ERR_PTR on failure
• */

+struct tee_shm *tee_shm_register_fd(struct tee_context *ctx, int fd);

/**

• tee_shm_free() - Free shared memory
• @shm: Handle to shared memory to free

diff --git a/include/uapi/linux/tee.h b/include/uapi/linux/tee.h index d0430bee8292..d843cf980d98 100644 --- a/include/uapi/linux/tee.h +++ b/include/uapi/linux/tee.h @@ -378,6 +378,37 @@ struct tee_ioctl_shm_register_data { __s32 id; };

+/**

• • struct tee_ioctl_shm_register_fd_data - Shared memory registering argument
• • @fd: [in] File descriptor identifying dmabuf reference
• • @size: [out] Size of referenced memory
• • @flags: [in] Flags to/from allocation.
• • @id: [out] Identifier of the shared memory
• • The flags field should currently be zero as input. Updated by the call
• • with actual flags as defined by TEE_IOCTL_SHM_* above.
• • This structure is used as argument for TEE_IOC_SHM_REGISTER_FD below.
• */

+struct tee_ioctl_shm_register_fd_data {

• __s64 fd;
  

• __u64 size;
  

• __u32 flags;
  

• __s32 id;
  

+};

+/**

• • TEE_IOC_SHM_REGISTER_FD - register a shared memory from a file descriptor
• • Returns a file descriptor on success or < 0 on failure
• • The returned file descriptor refers to the shared memory object in the
• • kernel. The supplied file deccriptor can be closed if it's not needed
• • for other purposes. The shared memory is freed when the descriptor is
• • closed.
• */

+#define TEE_IOC_SHM_REGISTER_FD _IOWR(TEE_IOC_MAGIC, TEE_IOC_BASE + 8, \

•                              struct tee_ioctl_shm_register_fd_data)
  

/**

• TEE_IOC_SHM_REGISTER - Register shared memory argument

-- 2.43.0