Re: [PATCH v12 08/13] net, arm64: untag user pointers in tcp_zerocopy_receive
From: Eric Dumazet
Date: Mon Mar 18 2019 - 13:35:32 EST
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
@@ -1761,6 +1761,8 @@ static int tcp_zerocopy_receive(struct sock *sk,
if (address & (PAGE_SIZE - 1) || address != zc->address)
+ address = untagged_addr(address);
if (sk->sk_state == TCP_LISTEN)