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Subject[PATCH v2] tee: handle lookup of shm with reference count 0
Date
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: 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>
---
v1->v2
* fix copyright years in drivers/tee/tee_shm.c
* update kerneldoc comment for struct tee_shm with the reference counter

drivers/tee/tee_shm.c | 174 +++++++++++++++-------------------------
include/linux/tee_drv.h | 4 +-
2 files changed, 68 insertions(+), 110 deletions(-)

diff --git a/drivers/tee/tee_shm.c b/drivers/tee/tee_shm.c
index 8a8deb95e918..499fccba3d74 100644
--- a/drivers/tee/tee_shm.c
+++ b/drivers/tee/tee_shm.c
@@ -1,20 +1,17 @@
// 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>
#include <linux/uio.h>
-#include <linux/module.h>
#include "tee_private.h"

-MODULE_IMPORT_NS(DMA_BUF);
-
static void release_registered_pages(struct tee_shm *shm)
{
if (shm->pages) {
@@ -31,16 +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;

@@ -67,45 +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;
@@ -140,6 +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)
@@ -153,10 +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);
@@ -164,28 +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:
@@ -246,6 +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;
@@ -306,22 +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) {
@@ -339,6 +255,35 @@ struct tee_shm *tee_shm_register(struct tee_context *ctx, unsigned long addr,
}
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
@@ -351,10 +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;
}

@@ -364,17 +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);

@@ -481,10 +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;
}
@@ -496,7 +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 a1f03461369b..cf5999626e28 100644
--- 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, shared
* with user space
@@ -214,7 +214,7 @@ struct tee_shm {
unsigned int offset;
struct page **pages;
size_t num_pages;
- struct dma_buf *dmabuf;
+ refcount_t refcount;
u32 flags;
int id;
u64 sec_world_id;
--
2.31.1
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