Hi guys ! I was helping with a small driver when I stumbled upon a comment from a reviwer pointing to an old lwn article talking about deprecating set_fs due to security concerns:
https://lwn.net/Articles/722267/ Now, this is a very simple driver running on a small/slow ARM SoC, which reads from a FIFO and writes into a destination buffer. It provides 2 interfaces, a userspace one (read syscall) and an in- kernel one since some other kernel drivers use it as a transport. My existing implementation uses the good old construct of doing put_user() in the low level FIFO pumping code, and have the in-kernel API do: old_fs = get_fs(); set_fs(KERNEL_DS); rc = __sbefifo_submit(sbefifo, command, cmd_len, response, resp_len); set_fs(old_fs); Which is simple, turns into fairly efficient code on that simple device, and doesn't seem to have security issues... That said, following the advice in that article, I tried to look at the iovec stuff and noticed: - The APIs are almost entirely undocumented (or did I look in the wrong place ?) - The code in lib/iov_iter.c is rather ... unreadable - It's also significantly more complex, thus would probably result in a slower driver (remember: small SoC). It's quite overkill for my simple use case. - There are very few users, set_fs(KERNEL_DS) is still the most common method used by drivers. Hence my question: Is is still acceptable these days to use set_fs(KERNEL_DS) for simple cases like this ? Or is it really deprecated and all new users should use the iovec's ? Cheers, Ben.
