[PATCH v4] usb: gadget: f_fs: try to fix AIO issue under ARM 64 bit TAGGED mode

[Macpaul Lin]

This issue was found when adbd trying to open functionfs with AIO mode.
Usually, we need to set "setprop sys.usb.ffs.aio_compat 0" to enable
adbd with AIO mode on Android.

When adbd is opening functionfs, it will try to read 24 bytes at the
first read I/O control. If this reading has been failed, adbd will
try to send FUNCTIONFS_CLEAR_HALT to functionfs. When adbd is in AIO
mode, functionfs will be acted with asyncronized I/O path. After the
successful read transfer has been completed by gadget hardware, the
following series of functions will be called.
  ffs_epfile_async_io_complete() -> ffs_user_copy_worker() ->
    copy_to_iter() -> _copy_to_iter() -> copyout() ->
    iterate_and_advance() -> iterate_iovec()

Adding debug trace to these functions, it has been found that in
copyout(), access_ok() will check if the user space address is valid
to write. However if CONFIG_ARM64_TAGGED_ADDR_ABI is enabled, adbd
always passes user space address start with "0x3C" to gadget's AIO
blocks. This tagged address will cause access_ok() check always fail.
Which causes later calculation in iterate_iovec() turn zero.
Copyout() won't copy data to user space since the length to be copied
"v.iov_len" will be zero. Finally leads ffs_copy_to_iter() always return
-EFAULT, causes adbd cannot open functionfs and send
FUNCTIONFS_CLEAR_HALT.

Signed-off-by: Macpaul Lin <macpaul.lin@xxxxxxxxxxxx>
Cc: Peter Chen <peter.chen@xxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Miles Chen <miles.chen@xxxxxxxxxxxx>
---
Changes for v4:
  - Abandon solution v3 by adding "TIF_TAGGED_ADDR" flag to gadget driver.
    According to Catalin's suggestion, change the solution by untagging 
    user space address passed by AIO in gadget driver.

Changes for v3:
  - Fix misspelling in commit message.
    Thanks for Peter's review.

Changes for v2:
  - Fix build error for 32-bit load. An #if defined(CONFIG_ARM64) still need
    for avoiding undeclared defines.

 drivers/usb/gadget/function/f_fs.c |   15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
index ce1d023..192935f 100644
--- a/drivers/usb/gadget/function/f_fs.c
+++ b/drivers/usb/gadget/function/f_fs.c
@@ -715,7 +715,20 @@ static void ffs_epfile_io_complete(struct usb_ep *_ep, struct usb_request *req)
 
 static ssize_t ffs_copy_to_iter(void *data, int data_len, struct iov_iter *iter)
 {
-	ssize_t ret = copy_to_iter(data, data_len, iter);
+	ssize_t ret;
+
+#if defined(CONFIG_ARM64)
+	/*
+	 * Replace tagged address passed by user space application before
+	 * copying.
+	 */
+	if (IS_ENABLED(CONFIG_ARM64_TAGGED_ADDR_ABI) &&
+		(iter->type == ITER_IOVEC)) {
+		*(unsigned long *)&iter->iov->iov_base =
+			(unsigned long)untagged_addr(iter->iov->iov_base);
+	}
+#endif
+	ret = copy_to_iter(data, data_len, iter);
 	if (likely(ret == data_len))
 		return ret;
 
-- 
1.7.9.5