Re: [PATCH v12 08/13] net, arm64: untag user pointers in tcp_zerocopy_receive

[Andrey Konovalov]

On Mon, Mar 18, 2019 at 6:35 PM Eric Dumazet <edumazet@xxxxxxxxxx> wrote:
>
> On Mon, Mar 18, 2019 at 10:18 AM Andrey Konovalov <andreyknvl@xxxxxxxxxx> wrote:
> >
> > This patch is a part of a series that extends arm64 kernel ABI to allow to
> > pass tagged user pointers (with the top byte set to something else other
> > than 0x00) as syscall arguments.
> >
> > tcp_zerocopy_receive() uses provided user pointers for vma lookups, which
> > can only by done with untagged pointers.
> >
> > Untag user pointers in this function.
> >
> > Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
> > ---
> >  net/ipv4/tcp.c | 9 +++++++--
> >  1 file changed, 7 insertions(+), 2 deletions(-)
> >
> > diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> > index 6baa6dc1b13b..e76beb5ff1ff 100644
> > --- a/net/ipv4/tcp.c
> > +++ b/net/ipv4/tcp.c
> > @@ -1749,7 +1749,7 @@ EXPORT_SYMBOL(tcp_mmap);
> >  static int tcp_zerocopy_receive(struct sock *sk,
> >                                 struct tcp_zerocopy_receive *zc)
> >  {
> > -       unsigned long address = (unsigned long)zc->address;
> > +       unsigned long address;
> >         const skb_frag_t *frags = NULL;
> >         u32 length = 0, seq, offset;
> >         struct vm_area_struct *vma;
> > @@ -1758,7 +1758,12 @@ static int tcp_zerocopy_receive(struct sock *sk,
> >         int inq;
> >         int ret;
> >
> > -       if (address & (PAGE_SIZE - 1) || address != zc->address)
> > +       address = (unsigned long)untagged_addr(zc->address);
> > +
> > +       /* The second test in this if detects if the u64->unsigned long
> > +        * conversion had any truncated bits.
> > +        */
> > +       if (address & (PAGE_SIZE - 1) || address != untagged_addr(zc->address))
> >                 return -EINVAL;
> >
> >         if (sk->sk_state == TCP_LISTEN)
>
>
> This is quite ugly, the comment does not really help nor belong to this patch.
>
> What about using  untagged_addr()  only once ?
>
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index 6baa6dc1b13b0b94b1da238668b93e167cf444fe..855a1f68c1ea9b0d07a92bd7f5e7c24840a99d3d
> 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -1761,6 +1761,8 @@ static int tcp_zerocopy_receive(struct sock *sk,
>         if (address & (PAGE_SIZE - 1) || address != zc->address)
>                 return -EINVAL;
>
> +       address = untagged_addr(address);
> +
>         if (sk->sk_state == TCP_LISTEN)
>                 return -ENOTCONN;

Looks good, will do it like this in the next version. Thanks!