linux-kernel - Re: [PATCH v12 08/13] net, arm64: untag user pointers in tcp_zerocopy

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Date:   Mon, 18 Mar 2019 10:35:14 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     Andrey Konovalov <andreyknvl@...gle.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Mark Rutland <mark.rutland@....com>,
        Robin Murphy <robin.murphy@....com>,
        Kees Cook <keescook@...omium.org>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Shuah Khan <shuah@...nel.org>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        "David S. Miller" <davem@...emloft.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Kostya Serebryany <kcc@...gle.com>,
        Evgeniy Stepanov <eugenis@...gle.com>,
        Lee Smith <Lee.Smith@....com>,
        Ramana Radhakrishnan <Ramana.Radhakrishnan@....com>,
        Jacob Bramley <Jacob.Bramley@....com>,
        Ruben Ayrapetyan <Ruben.Ayrapetyan@....com>,
        Chintan Pandya <cpandya@...eaurora.org>,
        Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
        Dave Martin <Dave.Martin@....com>,
        Kevin Brodsky <kevin.brodsky@....com>,
        Szabolcs Nagy <Szabolcs.Nagy@....com>
Subject: Re: [PATCH v12 08/13] net, arm64: untag user pointers in tcp_zerocopy_receive

On Mon, Mar 18, 2019 at 10:18 AM Andrey Konovalov <andreyknvl@...gle.com> 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@...gle.com>
> ---
>  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;