Re: [PATCH v3] usb: gadget: f_fs: try to fix AIO issue under ARM 64 bit TAGGED mode

[Miles Chen]

On Tue, 2020-02-25 at 18:41 +0800, Macpaul Lin wrote:
> 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 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>
> ---
> Changes for v3:
>   - Fix misspelling in commit message.

Could you say "thank you" to Peter for his comment and add 
"Cc: Peter Chen <peter.chen@xxxxxxx>" to this patch, please?

> 
> 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 |    5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
> index ce1d023..728c260 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 +827,10 @@ static void ffs_user_copy_worker(struct work_struct *work)
>  	if (io_data->read && ret > 0) {
>  		mm_segment_t oldfs = get_fs();
>  
> +#if defined(CONFIG_ARM64)
> +		if (IS_ENABLED(CONFIG_ARM64_TAGGED_ADDR_ABI))
> +			set_thread_flag(TIF_TAGGED_ADDR);
> +#endif
>  		set_fs(USER_DS);
>  		use_mm(io_data->mm);
>  		ret = ffs_copy_to_iter(io_data->buf, ret, &io_data->data);