tee: handle lookup of shm with reference count 0

commit dfd0743f1d9ea76931510ed150334d571fbab49d upstream.

Since the tee subsystem does not keep a strong reference to its idle
shared memory buffers, it races with other threads that try to destroy a
shared memory through a close of its dma-buf fd or by unmapping the
memory.

In tee_shm_get_from_id() when a lookup in teedev->idr has been
successful, it is possible that the tee_shm is in the dma-buf teardown
path, but that path is blocked by the teedev mutex. Since we don't have
an API to tell if the tee_shm is in the dma-buf teardown path or not we
must find another way of detecting this condition.

Fix this by doing the reference counting directly on the tee_shm using a
new refcount_t refcount field. dma-buf is replaced by using
anon_inode_getfd() instead, this separates the life-cycle of the
underlying file from the tee_shm. tee_shm_put() is updated to hold the
mutex when decreasing the refcount to 0 and then remove the tee_shm from
teedev->idr before releasing the mutex. This means that the tee_shm can
never be found unless it has a refcount larger than 0.

Fixes: 967c9cca2cc5 ("tee: generic TEE subsystem")
Cc: stable@vger.kernel.org
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Lars Persson <larper@axis.com>
Reviewed-by: Sumit Garg <sumit.garg@linaro.org>
Reported-by: Patrik Lantz <patrik.lantz@axis.com>
[JW: backported to 4.14-stable]
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tee/tee_private.h b/drivers/tee/tee_private.h
index 21cb6be8bce94d91a052009a20410618d3e2c24b..4ef325f782d11ad30e7a419019445d3b205ce75a 100644 (file)
--- a/drivers/tee/tee_private.h
+++ b/drivers/tee/tee_private.h
@@ -31,7 +31,7 @@ struct tee_device;
  * @paddr:     physical address of the shared memory
  * @kaddr:     virtual address of the shared memory
  * @size:      size of shared memory
- * @dmabuf:    dmabuf used to for exporting to user space
+ * @refcount:  reference counter
  * @flags:     defined by TEE_SHM_* in tee_drv.h
  * @id:                unique id of a shared memory object on this device
  */
@@ -42,7 +42,7 @@ struct tee_shm {
        phys_addr_t paddr;
        void *kaddr;
        size_t size;
-       struct dma_buf *dmabuf;
+       refcount_t refcount;
        u32 flags;
        int id;
 };

diff --git a/drivers/tee/tee_shm.c b/drivers/tee/tee_shm.c
index ea3ce4e17b855275ba80dd7adca7ac91fb8b3f46..b8f171b9658b84703ef61aabbdf0b0ac58e9ed17 100644 (file)
--- a/drivers/tee/tee_shm.c
+++ b/drivers/tee/tee_shm.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2015-2016, Linaro Limited
+ * Copyright (c) 2015-2017, 2019-2021 Linaro Limited
  *
  * This software is licensed under the terms of the GNU General Public
  * License version 2, as published by the Free Software Foundation, and
@@ -11,26 +11,19 @@
  * GNU General Public License for more details.
  *
  */
+#include <linux/anon_inodes.h>
 #include <linux/device.h>
-#include <linux/dma-buf.h>
-#include <linux/fdtable.h>
 #include <linux/idr.h>
+#include <linux/mm.h>
 #include <linux/sched.h>
 #include <linux/slab.h>
 #include <linux/tee_drv.h>
 #include "tee_private.h"
 
-static void tee_shm_release(struct tee_shm *shm)
+static void tee_shm_release(struct tee_device *teedev, struct tee_shm *shm)
 {
-       struct tee_device *teedev = shm->teedev;
        struct tee_shm_pool_mgr *poolm;
 
-       mutex_lock(&teedev->mutex);
-       idr_remove(&teedev->idr, shm->id);
-       if (shm->ctx)
-               list_del(&shm->link);
-       mutex_unlock(&teedev->mutex);
-
        if (shm->flags & TEE_SHM_DMA_BUF)
                poolm = &teedev->pool->dma_buf_mgr;
        else
@@ -42,53 +35,6 @@ static void tee_shm_release(struct tee_shm *shm)
        tee_device_put(teedev);
 }
 
-static struct sg_table *tee_shm_op_map_dma_buf(struct dma_buf_attachment
-                       *attach, enum dma_data_direction dir)
-{
-       return NULL;
-}
-
-static void tee_shm_op_unmap_dma_buf(struct dma_buf_attachment *attach,
-                                    struct sg_table *table,
-                                    enum dma_data_direction dir)
-{
-}
-
-static void tee_shm_op_release(struct dma_buf *dmabuf)
-{
-       struct tee_shm *shm = dmabuf->priv;
-
-       tee_shm_release(shm);
-}
-
-static void *tee_shm_op_map_atomic(struct dma_buf *dmabuf, unsigned long pgnum)
-{
-       return NULL;
-}
-
-static void *tee_shm_op_map(struct dma_buf *dmabuf, unsigned long pgnum)
-{
-       return NULL;
-}
-
-static int tee_shm_op_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma)
-{
-       struct tee_shm *shm = dmabuf->priv;
-       size_t size = vma->vm_end - vma->vm_start;
-
-       return remap_pfn_range(vma, vma->vm_start, shm->paddr >> PAGE_SHIFT,
-                              size, vma->vm_page_prot);
-}
-
-static const struct dma_buf_ops tee_shm_dma_buf_ops = {
-       .map_dma_buf = tee_shm_op_map_dma_buf,
-       .unmap_dma_buf = tee_shm_op_unmap_dma_buf,
-       .release = tee_shm_op_release,
-       .map_atomic = tee_shm_op_map_atomic,
-       .map = tee_shm_op_map,
-       .mmap = tee_shm_op_mmap,
-};
-
 /**
  * tee_shm_alloc() - Allocate shared memory
  * @ctx:       Context that allocates the shared memory
@@ -135,6 +81,7 @@ struct tee_shm *tee_shm_alloc(struct tee_context *ctx, size_t size, u32 flags)
                goto err_dev_put;
        }
 
+       refcount_set(&shm->refcount, 1);
        shm->flags = flags;
        shm->teedev = teedev;
        shm->ctx = ctx;
@@ -157,29 +104,11 @@ struct tee_shm *tee_shm_alloc(struct tee_context *ctx, size_t size, u32 flags)
                goto err_pool_free;
        }
 
-       if (flags & TEE_SHM_DMA_BUF) {
-               DEFINE_DMA_BUF_EXPORT_INFO(exp_info);
-
-               exp_info.ops = &tee_shm_dma_buf_ops;
-               exp_info.size = shm->size;
-               exp_info.flags = O_RDWR;
-               exp_info.priv = shm;
-
-               shm->dmabuf = dma_buf_export(&exp_info);
-               if (IS_ERR(shm->dmabuf)) {
-                       ret = ERR_CAST(shm->dmabuf);
-                       goto err_rem;
-               }
-       }
        mutex_lock(&teedev->mutex);
        list_add_tail(&shm->link, &ctx->list_shm);
        mutex_unlock(&teedev->mutex);
 
        return shm;
-err_rem:
-       mutex_lock(&teedev->mutex);
-       idr_remove(&teedev->idr, shm->id);
-       mutex_unlock(&teedev->mutex);
 err_pool_free:
        poolm->ops->free(poolm, shm);
 err_kfree:
@@ -190,6 +119,31 @@ err_dev_put:
 }
 EXPORT_SYMBOL_GPL(tee_shm_alloc);
 
+static int tee_shm_fop_release(struct inode *inode, struct file *filp)
+{
+       tee_shm_put(filp->private_data);
+       return 0;
+}
+
+static int tee_shm_fop_mmap(struct file *filp, struct vm_area_struct *vma)
+{
+       struct tee_shm *shm = filp->private_data;
+       size_t size = vma->vm_end - vma->vm_start;
+
+       /* check for overflowing the buffer's size */
+       if (vma->vm_pgoff + vma_pages(vma) > shm->size >> PAGE_SHIFT)
+               return -EINVAL;
+
+       return remap_pfn_range(vma, vma->vm_start, shm->paddr >> PAGE_SHIFT,
+                              size, vma->vm_page_prot);
+}
+
+static const struct file_operations tee_shm_fops = {
+       .owner = THIS_MODULE,
+       .release = tee_shm_fop_release,
+       .mmap = tee_shm_fop_mmap,
+};
+
 /**
  * tee_shm_get_fd() - Increase reference count and return file descriptor
  * @shm:       Shared memory handle
@@ -203,10 +157,11 @@ int tee_shm_get_fd(struct tee_shm *shm)
        if ((shm->flags & req_flags) != req_flags)
                return -EINVAL;
 
-       get_dma_buf(shm->dmabuf);
-       fd = dma_buf_fd(shm->dmabuf, O_CLOEXEC);
+       /* matched by tee_shm_put() in tee_shm_op_release() */
+       refcount_inc(&shm->refcount);
+       fd = anon_inode_getfd("tee_shm", &tee_shm_fops, shm, O_RDWR);
        if (fd < 0)
-               dma_buf_put(shm->dmabuf);
+               tee_shm_put(shm);
        return fd;
 }
 
@@ -216,17 +171,7 @@ int tee_shm_get_fd(struct tee_shm *shm)
  */
 void tee_shm_free(struct tee_shm *shm)
 {
-       /*
-        * dma_buf_put() decreases the dmabuf reference counter and will
-        * call tee_shm_release() when the last reference is gone.
-        *
-        * In the case of driver private memory we call tee_shm_release
-        * directly instead as it doesn't have a reference counter.
-        */
-       if (shm->flags & TEE_SHM_DMA_BUF)
-               dma_buf_put(shm->dmabuf);
-       else
-               tee_shm_release(shm);
+       tee_shm_put(shm);
 }
 EXPORT_SYMBOL_GPL(tee_shm_free);
 
@@ -327,10 +272,15 @@ struct tee_shm *tee_shm_get_from_id(struct tee_context *ctx, int id)
        teedev = ctx->teedev;
        mutex_lock(&teedev->mutex);
        shm = idr_find(&teedev->idr, id);
+       /*
+        * If the tee_shm was found in the IDR it must have a refcount
+        * larger than 0 due to the guarantee in tee_shm_put() below. So
+        * it's safe to use refcount_inc().
+        */
        if (!shm || shm->ctx != ctx)
                shm = ERR_PTR(-EINVAL);
-       else if (shm->flags & TEE_SHM_DMA_BUF)
-               get_dma_buf(shm->dmabuf);
+       else
+               refcount_inc(&shm->refcount);
        mutex_unlock(&teedev->mutex);
        return shm;
 }
@@ -353,7 +303,24 @@ EXPORT_SYMBOL_GPL(tee_shm_get_id);
  */
 void tee_shm_put(struct tee_shm *shm)
 {
-       if (shm->flags & TEE_SHM_DMA_BUF)
-               dma_buf_put(shm->dmabuf);
+       struct tee_device *teedev = shm->teedev;
+       bool do_release = false;
+
+       mutex_lock(&teedev->mutex);
+       if (refcount_dec_and_test(&shm->refcount)) {
+               /*
+                * refcount has reached 0, we must now remove it from the
+                * IDR before releasing the mutex.  This will guarantee
+                * that the refcount_inc() in tee_shm_get_from_id() never
+                * starts from 0.
+                */
+               if (shm->ctx)
+                       list_del(&shm->link);
+               do_release = true;
+       }
+       mutex_unlock(&teedev->mutex);
+
+       if (do_release)
+               tee_shm_release(teedev, shm);
 }
 EXPORT_SYMBOL_GPL(tee_shm_put);