[PATCH] 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
fisrt 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 gdaget'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 userspace 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>
---
 drivers/usb/gadget/function/f_fs.c |    3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
index ce1d023..b21541a 100644
--- a/drivers/usb/gadget/function/f_fs.c
+++ b/drivers/usb/gadget/function/f_fs.c
@@ -35,6 +35,7 @@
 #include <linux/mmu_context.h>
 #include <linux/poll.h>
 #include <linux/eventfd.h>
+#include <linux/thread_info.h>
 
 #include "u_fs.h"
 #include "u_f.h"
@@ -826,6 +827,8 @@ static void ffs_user_copy_worker(struct work_struct *work)
 	if (io_data->read && ret > 0) {
 		mm_segment_t oldfs = get_fs();
 
+		if (IS_ENABLED(CONFIG_ARM64_TAGGED_ADDR_ABI))
+			set_thread_flag(TIF_TAGGED_ADDR);
 		set_fs(USER_DS);
 		use_mm(io_data->mm);
 		ret = ffs_copy_to_iter(io_data->buf, ret, &io_data->data);
-- 
1.7.9.5