linux-kernel - Re: [RFC,iov_iter v2 3/8] iov_iter: add copyin

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Date:   Mon, 13 Jun 2022 04:25:39 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Joe Damato <jdamato@...tly.com>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [RFC,iov_iter v2 3/8] iov_iter: add copyin_iovec helper

On Sun, Jun 12, 2022 at 01:57:52AM -0700, Joe Damato wrote:
> copyin_iovec is a helper which wraps copyin and selects the right copy
> method based on the iter_copy_type.
> 
> Signed-off-by: Joe Damato <jdamato@...tly.com>
> ---
>  lib/iov_iter.c | 19 ++++++++++++++-----
>  1 file changed, 14 insertions(+), 5 deletions(-)
> 
> diff --git a/lib/iov_iter.c b/lib/iov_iter.c
> index d32d7e5..6720cb2 100644
> --- a/lib/iov_iter.c
> +++ b/lib/iov_iter.c
> @@ -168,6 +168,15 @@ static int copyin(void *to, const void __user *from, size_t n)
>  	return n;
>  }
>  
> +static int copyin_iovec(void *to, const void __user *from, size_t n,
> +			struct iov_iter *i)
> +{
> +	if (unlikely(iov_iter_copy_is_nt(i)))
> +		return __copy_from_user_nocache(to, from, n);
> +	else
> +		return copyin(to, from, n);
> +}

Just a sanity check - your testing is *not* with KASAN/KCSAN, right?

And BTW, why is that only on the userland side?  If you are doing
that at all, it would make sense to cover the memcpy() side as
well...