virtiofs: use pages instead of pointer for kernel direct IO

Hou Tao · openunix · commit a98bbb2654b9 · 2025-07-11T15:36:07.000+08:00
BugLink: https://bugs.launchpad.net/bugs/2101915 [ Upstream commit 4174867 ] When trying to insert a 10MB kernel module kept in a virtio-fs with cache disabled, the following warning was reported: ------------[ cut here ]------------ WARNING: CPU: 1 PID: 404 at mm/page_alloc.c:4551 ...... Modules linked in: CPU: 1 PID: 404 Comm: insmod Not tainted 6.9.0-rc5+ torvalds#123 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996) ...... RIP: 0010:__alloc_pages+0x2bf/0x380 ...... Call Trace: <TASK> ? __warn+0x8e/0x150 ? __alloc_pages+0x2bf/0x380 __kmalloc_large_node+0x86/0x160 __kmalloc+0x33c/0x480 virtio_fs_enqueue_req+0x240/0x6d0 virtio_fs_wake_pending_and_unlock+0x7f/0x190 queue_request_and_unlock+0x55/0x60 fuse_simple_request+0x152/0x2b0 fuse_direct_io+0x5d2/0x8c0 fuse_file_read_iter+0x121/0x160 __kernel_read+0x151/0x2d0 kernel_read+0x45/0x50 kernel_read_file+0x1a9/0x2a0 init_module_from_file+0x6a/0xe0 idempotent_init_module+0x175/0x230 __x64_sys_finit_module+0x5d/0xb0 x64_sys_call+0x1c3/0x9e0 do_syscall_64+0x3d/0xc0 entry_SYSCALL_64_after_hwframe+0x4b/0x53 ...... </TASK> ---[ end trace 0000000000000000 ]--- The warning is triggered as follows: 1) syscall finit_module() handles the module insertion and it invokes kernel_read_file() to read the content of the module first. 2) kernel_read_file() allocates a 10MB buffer by using vmalloc() and passes it to kernel_read(). kernel_read() constructs a kvec iter by using iov_iter_kvec() and passes it to fuse_file_read_iter(). 3) virtio-fs disables the cache, so fuse_file_read_iter() invokes fuse_direct_io(). As for now, the maximal read size for kvec iter is only limited by fc->max_read. For virtio-fs, max_read is UINT_MAX, so fuse_direct_io() doesn't split the 10MB buffer. It saves the address and the size of the 10MB-sized buffer in out_args[0] of a fuse request and passes the fuse request to virtio_fs_wake_pending_and_unlock(). 4) virtio_fs_wake_pending_and_unlock() uses virtio_fs_enqueue_req() to queue the request. Because virtiofs need DMA-able address, so virtio_fs_enqueue_req() uses kmalloc() to allocate a bounce buffer for all fuse args, copies these args into the bounce buffer and passed the physical address of the bounce buffer to virtiofsd. The total length of these fuse args for the passed fuse request is about 10MB, so copy_args_to_argbuf() invokes kmalloc() with a 10MB size parameter and it triggers the warning in __alloc_pages(): if (WARN_ON_ONCE_GFP(order > MAX_PAGE_ORDER, gfp)) return NULL; 5) virtio_fs_enqueue_req() will retry the memory allocation in a kworker, but it won't help, because kmalloc() will always return NULL due to the abnormal size and finit_module() will hang forever. A feasible solution is to limit the value of max_read for virtio-fs, so the length passed to kmalloc() will be limited. However it will affect the maximal read size for normal read. And for virtio-fs write initiated from kernel, it has the similar problem but now there is no way to limit fc->max_write in kernel. So instead of limiting both the values of max_read and max_write in kernel, introducing use_pages_for_kvec_io in fuse_conn and setting it as true in virtiofs. When use_pages_for_kvec_io is enabled, fuse will use pages instead of pointer to pass the KVEC_IO data. After switching to pages for KVEC_IO data, these pages will be used for DMA through virtio-fs. If these pages are backed by vmalloc(), {flush|invalidate}_kernel_vmap_range() are necessary to flush or invalidate the cache before the DMA operation. So add two new fields in fuse_args_pages to record the base address of vmalloc area and the condition indicating whether invalidation is needed. Perform the flush in fuse_get_user_pages() for write operations and the invalidation in fuse_release_user_pages() for read operations. It may seem necessary to introduce another field in fuse_conn to indicate that these KVEC_IO pages are used for DMA, However, considering that virtio-fs is currently the only user of use_pages_for_kvec_io, just reuse use_pages_for_kvec_io to indicate that these pages will be used for DMA. Fixes: a62a8ef ("virtio-fs: add virtiofs filesystem") Signed-off-by: Hou Tao <houtao1@huawei.com> Tested-by: Jingbo Xu <jefflexu@linux.alibaba.com> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com> Signed-off-by: Sasha Levin <sashal@kernel.org> [koichiroden: adjusted context due to missing commits: 738adad ("fuse: Fix missing FOLL_PIN for direct-io") 7dc4e97 ("fuse: introduce FUSE_PASSTHROUGH capability")] CVE-2024-53219 Signed-off-by: Koichiro Den <koichiro.den@canonical.com> Signed-off-by: Stefan Bader <stefan.bader@canonical.com> (cherry picked from commit 6996dac)
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
@@ -624,7 +624,7 @@ void fuse_read_args_fill(struct fuse_io_args *ia, struct file *file, loff_t pos,
 	args->out_args[0].size = count;
 }
 
-static void fuse_release_user_pages(struct fuse_args_pages *ap,
+static void fuse_release_user_pages(struct fuse_args_pages *ap, ssize_t nres,
 				    bool should_dirty)
 {
 	unsigned int i;
@@ -634,6 +634,9 @@ static void fuse_release_user_pages(struct fuse_args_pages *ap,
 			set_page_dirty_lock(ap->pages[i]);
 		put_page(ap->pages[i]);
 	}
+
+	if (nres > 0 && ap->args.invalidate_vmap)
+		invalidate_kernel_vmap_range(ap->args.vmap_base, nres);
 }
 
 static void fuse_io_release(struct kref *kref)
@@ -732,25 +735,29 @@ static void fuse_aio_complete_req(struct fuse_mount *fm, struct fuse_args *args,
 	struct fuse_io_args *ia = container_of(args, typeof(*ia), ap.args);
 	struct fuse_io_priv *io = ia->io;
 	ssize_t pos = -1;
-
-	fuse_release_user_pages(&ia->ap, io->should_dirty);
+	size_t nres;
 
 	if (err) {
 		/* Nothing */
 	} else if (io->write) {
 		if (ia->write.out.size > ia->write.in.size) {
 			err = -EIO;
-		} else if (ia->write.in.size != ia->write.out.size) {
-			pos = ia->write.in.offset - io->offset +
-				ia->write.out.size;
+		} else {
+			nres = ia->write.out.size;
+			if (ia->write.in.size != ia->write.out.size)
+				pos = ia->write.in.offset - io->offset +
+				      ia->write.out.size;
 		}
 	} else {
 		u32 outsize = args->out_args[0].size;
 
+		nres = outsize;
 		if (ia->read.in.size != outsize)
 			pos = ia->read.in.offset - io->offset + outsize;
 	}
 
+	fuse_release_user_pages(&ia->ap, err ?: nres, io->should_dirty);
+
 	fuse_aio_complete(io, err, pos);
 	fuse_io_free(ia);
 }
@@ -1366,24 +1373,37 @@ static inline size_t fuse_get_frag_size(const struct iov_iter *ii,
 
 static int fuse_get_user_pages(struct fuse_args_pages *ap, struct iov_iter *ii,
 			       size_t *nbytesp, int write,
-			       unsigned int max_pages)
+			       unsigned int max_pages,
+			       bool use_pages_for_kvec_io)
 {
+	bool flush_or_invalidate = false;
 	size_t nbytes = 0;  /* # bytes already packed in req */
 	ssize_t ret = 0;
 
-	/* Special case for kernel I/O: can copy directly into the buffer */
+	/* Special case for kernel I/O: can copy directly into the buffer.
+	 * However if the implementation of fuse_conn requires pages instead of
+	 * pointer (e.g., virtio-fs), use iov_iter_extract_pages() instead.
+	 */
 	if (iov_iter_is_kvec(ii)) {
-		unsigned long user_addr = fuse_get_user_addr(ii);
-		size_t frag_size = fuse_get_frag_size(ii, *nbytesp);
+		void *user_addr = (void *)fuse_get_user_addr(ii);
 
-		if (write)
-			ap->args.in_args[1].value = (void *) user_addr;
-		else
-			ap->args.out_args[0].value = (void *) user_addr;
+		if (!use_pages_for_kvec_io) {
+			size_t frag_size = fuse_get_frag_size(ii, *nbytesp);
 
-		iov_iter_advance(ii, frag_size);
-		*nbytesp = frag_size;
-		return 0;
+			if (write)
+				ap->args.in_args[1].value = user_addr;
+			else
+				ap->args.out_args[0].value = user_addr;
+
+			iov_iter_advance(ii, frag_size);
+			*nbytesp = frag_size;
+			return 0;
+		}
+
+		if (is_vmalloc_addr(user_addr)) {
+			ap->args.vmap_base = user_addr;
+			flush_or_invalidate = true;
+		}
 	}
 
 	while (nbytes < *nbytesp && ap->num_pages < max_pages) {
@@ -1409,6 +1429,10 @@ static int fuse_get_user_pages(struct fuse_args_pages *ap, struct iov_iter *ii,
 			(PAGE_SIZE - ret) & (PAGE_SIZE - 1);
 	}
 
+	if (write && flush_or_invalidate)
+		flush_kernel_vmap_range(ap->args.vmap_base, nbytes);
+
+	ap->args.invalidate_vmap = !write && flush_or_invalidate;
 	ap->args.user_pages = true;
 	if (write)
 		ap->args.in_pages = true;
@@ -1476,7 +1500,7 @@ ssize_t fuse_direct_io(struct fuse_io_priv *io, struct iov_iter *iter,
 		size_t nbytes = min(count, nmax);
 
 		err = fuse_get_user_pages(&ia->ap, iter, &nbytes, write,
-					  max_pages);
+					  max_pages, fc->use_pages_for_kvec_io);
 		if (err && !nbytes)
 			break;
 
@@ -1490,7 +1514,7 @@ ssize_t fuse_direct_io(struct fuse_io_priv *io, struct iov_iter *iter,
 		}
 
 		if (!io->async || nres < 0) {
-			fuse_release_user_pages(&ia->ap, io->should_dirty);
+			fuse_release_user_pages(&ia->ap, nres, io->should_dirty);
 			fuse_io_free(ia);
 		}
 		ia = NULL;
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
@@ -283,9 +283,12 @@ struct fuse_args {
 	bool page_replace:1;
 	bool may_block:1;
 	bool is_ext:1;
+	bool invalidate_vmap:1;
 	struct fuse_in_arg in_args[3];
 	struct fuse_arg out_args[2];
 	void (*end)(struct fuse_mount *fm, struct fuse_args *args, int error);
+	/* Used for kvec iter backed by vmalloc address */
+	void *vmap_base;
 };
 
 struct fuse_args_pages {
@@ -818,6 +821,9 @@ struct fuse_conn {
 	/* Is statx not implemented by fs? */
 	unsigned int no_statx:1;
 
+	/* Use pages instead of pointer for kernel I/O */
+	unsigned int use_pages_for_kvec_io:1;
+
 	/** The number of requests waiting for completion */
 	atomic_t num_waiting;
 
diff --git a/fs/fuse/virtio_fs.c b/fs/fuse/virtio_fs.c
@@ -1505,6 +1505,7 @@ static int virtio_fs_get_tree(struct fs_context *fsc)
 	fc->delete_stale = true;
 	fc->auto_submounts = true;
 	fc->sync_fs = true;
+	fc->use_pages_for_kvec_io = true;
 
 	/* Tell FUSE to split requests that exceed the virtqueue's size */
 	fc->max_pages_limit = min_t(unsigned int, fc->max_pages_limit,
