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    SubjectRe: [PATCH v11 08/14] net, arm64: untag user pointers in tcp_zerocopy_receive
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    On 03/15/2019 12:51 PM, Andrey Konovalov 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@google.com>
    > ---
    > net/ipv4/tcp.c | 2 ++
    > 1 file changed, 2 insertions(+)
    >
    > diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
    > index 6baa6dc1b13b..89db3b4fc753 100644
    > --- a/net/ipv4/tcp.c
    > +++ b/net/ipv4/tcp.c
    > @@ -1758,6 +1758,8 @@ static int tcp_zerocopy_receive(struct sock *sk,
    > int inq;
    > int ret;
    >
    > + address = untagged_addr(address);
    > +
    > if (address & (PAGE_SIZE - 1) || address != zc->address)

    The second test will fail, if the top bits are changed in address but not in zc->address

    > return -EINVAL;
    >
    >

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