tee: handle lookup of shm with reference count 0

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.

Jens Wiklander committed 4 years ago

Commit dfd07431 parent d58071a2 files · +68 −110Browse files

Unified · Split

2 files

drivers/tee/tee_shm.c +66 −108
include/linux/tee_drv.h +2 −2

drivers/tee/tee_shm.c+66−108

@@ -1,20 +1,17 @@
1	1	// SPDX-License-Identifier: GPL-2.0-only
2	2	/*
3		− * Copyright (c) 2015-2016, Linaro Limited
	3	+ * Copyright (c) 2015-2017, 2019-2021 Linaro Limited
4	4	*/
	5	+#include <linux/anon_inodes.h>
5	6	#include <linux/device.h>
6		−#include <linux/dma-buf.h>
7		−#include <linux/fdtable.h>
8	7	#include <linux/idr.h>
	8	+#include <linux/mm.h>
9	9	#include <linux/sched.h>
10	10	#include <linux/slab.h>
11	11	#include <linux/tee_drv.h>
12	12	#include <linux/uio.h>
13		−#include <linux/module.h>
14	13	#include "tee_private.h"
15	14
16		−MODULE_IMPORT_NS(DMA_BUF);
17		−
18	15	static void release_registered_pages(struct tee_shm *shm)
19	16	{
20	17	if (shm->pages) {
@@ -31,16 +28,8 @@ static void release_registered_pages(struct tee_shm *shm) · 10 unmodified lines
31	28	}
32	29	}
33	30
34		−static void tee_shm_release(struct tee_shm *shm)
	31	+static void tee_shm_release(struct tee_device teedev, struct tee_shm shm)
35	32	{
36		− struct tee_device *teedev = shm->ctx->teedev;
37		−
38		− if (shm->flags & TEE_SHM_DMA_BUF) {
39		− mutex_lock(&teedev->mutex);
40		− idr_remove(&teedev->idr, shm->id);
41		− mutex_unlock(&teedev->mutex);
42		− }
43		−
44	33	if (shm->flags & TEE_SHM_POOL) {
45	34	struct tee_shm_pool_mgr *poolm;
46	35
@@ -67,45 +56,6 @@ static void tee_shm_release(struct tee_shm *shm) · 20 unmodified lines
67	56	tee_device_put(teedev);
68	57	}
69	58
70		−static struct sg_table *tee_shm_op_map_dma_buf(struct dma_buf_attachment
71		− *attach, enum dma_data_direction dir)
72		−{
73		− return NULL;
74		−}
75		−
76		−static void tee_shm_op_unmap_dma_buf(struct dma_buf_attachment *attach,
77		− struct sg_table *table,
78		− enum dma_data_direction dir)
79		−{
80		−}
81		−
82		−static void tee_shm_op_release(struct dma_buf *dmabuf)
83		−{
84		− struct tee_shm *shm = dmabuf->priv;
85		−
86		− tee_shm_release(shm);
87		−}
88		−
89		−static int tee_shm_op_mmap(struct dma_buf dmabuf, struct vm_area_struct vma)
90		−{
91		− struct tee_shm *shm = dmabuf->priv;
92		− size_t size = vma->vm_end - vma->vm_start;
93		−
94		− /* Refuse sharing shared memory provided by application */
95		− if (shm->flags & TEE_SHM_USER_MAPPED)
96		− return -EINVAL;
97		−
98		− return remap_pfn_range(vma, vma->vm_start, shm->paddr >> PAGE_SHIFT,
99		− size, vma->vm_page_prot);
100		−}
101		−
102		−static const struct dma_buf_ops tee_shm_dma_buf_ops = {
103		− .map_dma_buf = tee_shm_op_map_dma_buf,
104		− .unmap_dma_buf = tee_shm_op_unmap_dma_buf,
105		− .release = tee_shm_op_release,
106		− .mmap = tee_shm_op_mmap,
107		−};
108		−
109	59	struct tee_shm tee_shm_alloc(struct tee_context ctx, size_t size, u32 flags)
110	60	{
111	61	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) · 28 unmodified lines
140	90	goto err_dev_put;
141	91	}
142	92
	93	+ refcount_set(&shm->refcount, 1);
143	94	shm->flags = flags \| TEE_SHM_POOL;
144	95	shm->ctx = ctx;
145	96	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) · 7 unmodified lines
153	104	goto err_kfree;
154	105	}
155	106
156		−
157	107	if (flags & TEE_SHM_DMA_BUF) {
158		− DEFINE_DMA_BUF_EXPORT_INFO(exp_info);
159		−
160	108	mutex_lock(&teedev->mutex);
161	109	shm->id = idr_alloc(&teedev->idr, shm, 1, 0, GFP_KERNEL);
162	110	mutex_unlock(&teedev->mutex);
@@ -164,28 +112,11 @@ struct tee_shm tee_shm_alloc(struct tee_context ctx, size_t size, u32 flags) · 1 unmodified line
164	112	ret = ERR_PTR(shm->id);
165	113	goto err_pool_free;
166	114	}
167		−
168		− exp_info.ops = &tee_shm_dma_buf_ops;
169		− exp_info.size = shm->size;
170		− exp_info.flags = O_RDWR;
171		− exp_info.priv = shm;
172		−
173		− shm->dmabuf = dma_buf_export(&exp_info);
174		− if (IS_ERR(shm->dmabuf)) {
175		− ret = ERR_CAST(shm->dmabuf);
176		− goto err_rem;
177		− }
178	115	}
179	116
180	117	teedev_ctx_get(ctx);
181	118
182	119	return shm;
183		−err_rem:
184		− if (flags & TEE_SHM_DMA_BUF) {
185		− mutex_lock(&teedev->mutex);
186		− idr_remove(&teedev->idr, shm->id);
187		− mutex_unlock(&teedev->mutex);
188		− }
189	120	err_pool_free:
190	121	poolm->ops->free(poolm, shm);
191	122	err_kfree:
@@ -246,6 +177,7 @@ struct tee_shm tee_shm_register(struct tee_context ctx, unsigned long addr, · 54 unmodified lines
246	177	goto err;
247	178	}
248	179
	180	+ refcount_set(&shm->refcount, 1);
249	181	shm->flags = flags \| TEE_SHM_REGISTER;
250	182	shm->ctx = ctx;
251	183	shm->id = -1;
@@ -306,22 +238,6 @@ struct tee_shm tee_shm_register(struct tee_context ctx, unsigned long addr, · 54 unmodified lines
306	238	goto err;
307	239	}
308	240
309		− if (flags & TEE_SHM_DMA_BUF) {
310		− DEFINE_DMA_BUF_EXPORT_INFO(exp_info);
311		−
312		− exp_info.ops = &tee_shm_dma_buf_ops;
313		− exp_info.size = shm->size;
314		− exp_info.flags = O_RDWR;
315		− exp_info.priv = shm;
316		−
317		− shm->dmabuf = dma_buf_export(&exp_info);
318		− if (IS_ERR(shm->dmabuf)) {
319		− ret = ERR_CAST(shm->dmabuf);
320		− teedev->desc->ops->shm_unregister(ctx, shm);
321		− goto err;
322		− }
323		− }
324		−
325	241	return shm;
326	242	err:
327	243	if (shm) {
@@ -339,6 +255,35 @@ err: · 11 unmodified lines
339	255	}
340	256	EXPORT_SYMBOL_GPL(tee_shm_register);
341	257
	258	+static int tee_shm_fop_release(struct inode inode, struct file filp)
	259	+{
	260	+ tee_shm_put(filp->private_data);
	261	+ return 0;
	262	+}
	263	+
	264	+static int tee_shm_fop_mmap(struct file filp, struct vm_area_struct vma)
	265	+{
	266	+ struct tee_shm *shm = filp->private_data;
	267	+ size_t size = vma->vm_end - vma->vm_start;
	268	+
	269	+ /* Refuse sharing shared memory provided by application */
	270	+ if (shm->flags & TEE_SHM_USER_MAPPED)
	271	+ return -EINVAL;
	272	+
	273	+ /* check for overflowing the buffer's size */
	274	+ if (vma->vm_pgoff + vma_pages(vma) > shm->size >> PAGE_SHIFT)
	275	+ return -EINVAL;
	276	+
	277	+ return remap_pfn_range(vma, vma->vm_start, shm->paddr >> PAGE_SHIFT,
	278	+ size, vma->vm_page_prot);
	279	+}
	280	+
	281	+static const struct file_operations tee_shm_fops = {
	282	+ .owner = THIS_MODULE,
	283	+ .release = tee_shm_fop_release,
	284	+ .mmap = tee_shm_fop_mmap,
	285	+};
	286	+
342	287	/**
343	288	* tee_shm_get_fd() - Increase reference count and return file descriptor
344	289	* @shm: Shared memory handle
@@ -351,10 +296,11 @@ int tee_shm_get_fd(struct tee_shm *shm) · 6 unmodified lines
351	296	if (!(shm->flags & TEE_SHM_DMA_BUF))
352	297	return -EINVAL;
353	298
354		− get_dma_buf(shm->dmabuf);
355		− fd = dma_buf_fd(shm->dmabuf, O_CLOEXEC);
	299	+ /* matched by tee_shm_put() in tee_shm_op_release() */
	300	+ refcount_inc(&shm->refcount);
	301	+ fd = anon_inode_getfd("tee_shm", &tee_shm_fops, shm, O_RDWR);
356	302	if (fd < 0)
357		− dma_buf_put(shm->dmabuf);
	303	+ tee_shm_put(shm);
358	304	return fd;
359	305	}
360	306
@@ -364,17 +310,7 @@ int tee_shm_get_fd(struct tee_shm *shm) · 3 unmodified lines
364	310	*/
365	311	void tee_shm_free(struct tee_shm *shm)
366	312	{
367		− /*
368		− * dma_buf_put() decreases the dmabuf reference counter and will
369		− * call tee_shm_release() when the last reference is gone.
370		− *
371		− * In the case of driver private memory we call tee_shm_release
372		− * directly instead as it doesn't have a reference counter.
373		− */
374		− if (shm->flags & TEE_SHM_DMA_BUF)
375		− dma_buf_put(shm->dmabuf);
376		− else
377		− tee_shm_release(shm);
	313	+ tee_shm_put(shm);
378	314	}
379	315	EXPORT_SYMBOL_GPL(tee_shm_free);
380	316
@@ -481,10 +417,15 @@ struct tee_shm tee_shm_get_from_id(struct tee_context ctx, int id) · 100 unmodified lines
481	417	teedev = ctx->teedev;
482	418	mutex_lock(&teedev->mutex);
483	419	shm = idr_find(&teedev->idr, id);
	420	+ /*
	421	+ * If the tee_shm was found in the IDR it must have a refcount
	422	+ * larger than 0 due to the guarantee in tee_shm_put() below. So
	423	+ * it's safe to use refcount_inc().
	424	+ */
484	425	if (!shm \|\| shm->ctx != ctx)
485	426	shm = ERR_PTR(-EINVAL);
486		− else if (shm->flags & TEE_SHM_DMA_BUF)
487		− get_dma_buf(shm->dmabuf);
	427	+ else
	428	+ refcount_inc(&shm->refcount);
488	429	mutex_unlock(&teedev->mutex);
489	430	return shm;
490	431	}
@@ -496,7 +437,24 @@ EXPORT_SYMBOL_GPL(tee_shm_get_from_id); · 5 unmodified lines
496	437	*/
497	438	void tee_shm_put(struct tee_shm *shm)
498	439	{
499		− if (shm->flags & TEE_SHM_DMA_BUF)
500		− dma_buf_put(shm->dmabuf);
	440	+ struct tee_device *teedev = shm->ctx->teedev;
	441	+ bool do_release = false;
	442	+
	443	+ mutex_lock(&teedev->mutex);
	444	+ if (refcount_dec_and_test(&shm->refcount)) {
	445	+ /*
	446	+ * refcount has reached 0, we must now remove it from the
	447	+ * IDR before releasing the mutex. This will guarantee that
	448	+ * the refcount_inc() in tee_shm_get_from_id() never starts
	449	+ * from 0.
	450	+ */
	451	+ if (shm->flags & TEE_SHM_DMA_BUF)
	452	+ idr_remove(&teedev->idr, shm->id);
	453	+ do_release = true;
	454	+ }
	455	+ mutex_unlock(&teedev->mutex);
	456	+
	457	+ if (do_release)
	458	+ tee_shm_release(teedev, shm);
501	459	}
502	460	EXPORT_SYMBOL_GPL(tee_shm_put);

include/linux/tee_drv.h+2−2

@@ -195,7 +195,7 @@ int tee_session_calc_client_uuid(uuid_t *uuid, u32 connection_method, · 194 unmodified lines
195	195	* @offset: offset of buffer in user space
196	196	* @pages: locked pages from userspace
197	197	* @num_pages: number of locked pages
198		− * @dmabuf: dmabuf used to for exporting to user space
	198	+ * @refcount: reference counter
199	199	* @flags: defined by TEE_SHM_* in tee_drv.h
200	200	* @id: unique id of a shared memory object on this device, shared
201	201	* with user space
@@ -214,7 +214,7 @@ struct tee_shm { · 12 unmodified lines
214	214	unsigned int offset;
215	215	struct page **pages;
216	216	size_t num_pages;
217		− struct dma_buf *dmabuf;
	217	+ refcount_t refcount;
218	218	u32 flags;
219	219	int id;
220	220	u64 sec_world_id;