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>
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tee/tee_shm.c b/drivers/tee/tee_shm.c
index 8a9384a..499fccb 100644 (file)
--- a/drivers/tee/tee_shm.c
+++ b/drivers/tee/tee_shm.c
@@ -1,11 +1,11 @@
 // SPDX-License-Identifier: GPL-2.0-only
 /*
- * Copyright (c) 2015-2016, Linaro Limited
+ * Copyright (c) 2015-2017, 2019-2021 Linaro Limited
  */
+#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>
@@ -28,16 +28,8 @@ static void release_registered_pages(struct tee_shm *shm)
        }
 }
 
-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->ctx->teedev;
-
-       if (shm->flags & TEE_SHM_DMA_BUF) {
-               mutex_lock(&teedev->mutex);
-               idr_remove(&teedev->idr, shm->id);
-               mutex_unlock(&teedev->mutex);
-       }
-
        if (shm->flags & TEE_SHM_POOL) {
                struct tee_shm_pool_mgr *poolm;
 
@@ -64,45 +56,6 @@ 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 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;
-
-       /* Refuse sharing shared memory provided by application */
-       if (shm->flags & TEE_SHM_USER_MAPPED)
-               return -EINVAL;
-
-       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,
-       .mmap = tee_shm_op_mmap,
-};
-
 struct tee_shm *tee_shm_alloc(struct tee_context *ctx, size_t size, u32 flags)
 {
        struct tee_device *teedev = ctx->teedev;
@@ -137,6 +90,7 @@ 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 | TEE_SHM_POOL;
        shm->ctx = ctx;
        if (flags & TEE_SHM_DMA_BUF)
@@ -150,10 +104,7 @@ struct tee_shm *tee_shm_alloc(struct tee_context *ctx, size_t size, u32 flags)
                goto err_kfree;
        }
 
-
        if (flags & TEE_SHM_DMA_BUF) {
-               DEFINE_DMA_BUF_EXPORT_INFO(exp_info);
-
                mutex_lock(&teedev->mutex);
                shm->id = idr_alloc(&teedev->idr, shm, 1, 0, GFP_KERNEL);
                mutex_unlock(&teedev->mutex);
@@ -161,28 +112,11 @@ struct tee_shm *tee_shm_alloc(struct tee_context *ctx, size_t size, u32 flags)
                        ret = ERR_PTR(shm->id);
                        goto err_pool_free;
                }
-
-               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;
-               }
        }
 
        teedev_ctx_get(ctx);
 
        return shm;
-err_rem:
-       if (flags & TEE_SHM_DMA_BUF) {
-               mutex_lock(&teedev->mutex);
-               idr_remove(&teedev->idr, shm->id);
-               mutex_unlock(&teedev->mutex);
-       }
 err_pool_free:
        poolm->ops->free(poolm, shm);
 err_kfree:
@@ -243,6 +177,7 @@ struct tee_shm *tee_shm_register(struct tee_context *ctx, unsigned long addr,
                goto err;
        }
 
+       refcount_set(&shm->refcount, 1);
        shm->flags = flags | TEE_SHM_REGISTER;
        shm->ctx = ctx;
        shm->id = -1;
@@ -303,22 +238,6 @@ struct tee_shm *tee_shm_register(struct tee_context *ctx, unsigned long addr,
                goto err;
        }
 
-       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);
-                       teedev->desc->ops->shm_unregister(ctx, shm);
-                       goto err;
-               }
-       }
-
        return shm;
 err:
        if (shm) {
@@ -336,6 +255,35 @@ err:
 }
 EXPORT_SYMBOL_GPL(tee_shm_register);
 
+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;
+
+       /* Refuse sharing shared memory provided by application */
+       if (shm->flags & TEE_SHM_USER_MAPPED)
+               return -EINVAL;
+
+       /* 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
@@ -348,10 +296,11 @@ int tee_shm_get_fd(struct tee_shm *shm)
        if (!(shm->flags & TEE_SHM_DMA_BUF))
                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;
 }
 
@@ -361,17 +310,7 @@ 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);
 
@@ -478,10 +417,15 @@ 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;
 }
@@ -493,7 +437,24 @@ EXPORT_SYMBOL_GPL(tee_shm_get_from_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->ctx->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->flags & TEE_SHM_DMA_BUF)
+                       idr_remove(&teedev->idr, shm->id);
+               do_release = true;
+       }
+       mutex_unlock(&teedev->mutex);
+
+       if (do_release)
+               tee_shm_release(teedev, shm);
 }
 EXPORT_SYMBOL_GPL(tee_shm_put);

diff --git a/include/linux/tee_drv.h b/include/linux/tee_drv.h
index 3ebfea0..feda1dc 100644 (file)
--- a/include/linux/tee_drv.h
+++ b/include/linux/tee_drv.h
@@ -195,7 +195,7 @@ int tee_session_calc_client_uuid(uuid_t *uuid, u32 connection_method,
  * @offset:    offset of buffer in user space
  * @pages:     locked pages from userspace
  * @num_pages: number of locked pages
- * @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
  *
@@ -210,7 +210,7 @@ struct tee_shm {
        unsigned int offset;
        struct page **pages;
        size_t num_pages;
-       struct dma_buf *dmabuf;
+       refcount_t refcount;
        u32 flags;
        int id;
 };