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tee: handle lookup of shm with reference count 0
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commit dfd0743 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: 967c9cc ("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>
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@jenswi-linaro @gregkh
jenswi-linaro authored and gregkh committed Dec 29, 2021
1 parent 0ffb9f8 commit c05d8f6
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Showing 2 changed files with 68 additions and 107 deletions.
171 changes: 66 additions & 105 deletions drivers/tee/tee_shm.c
View file
@@ -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>
Expand All @@ -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;

Expand All @@ -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;
Expand Down Expand Up @@ -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)
Expand All @@ -150,39 +104,19 @@ 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);
if (shm->id < 0) {
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:
Expand Down Expand Up @@ -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;
Expand Down Expand Up @@ -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) {
Expand All @@ -336,6 +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
Expand All @@ -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;
}

Expand All @@ -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);

Expand Down Expand Up @@ -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;
}
Expand All @@ -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);
4 changes: 2 additions & 2 deletions include/linux/tee_drv.h
View file
Expand Up @@ -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
*
Expand All @@ -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;
};
Expand Down

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