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    SubjectRe: [PATCH v8 3/8] seccomp: add system call filtering using BPF
    On Thu, Feb 16, 2012 at 13:17, H. Peter Anvin <hpa@zytor.com> wrote:
    > The other thing that you really need in addition to system call number is
    > ABI identifier, since a syscall number may mean different things for
    > different entry points.  For example, on x86-64 system call number 4 is
    > write() if called via int $0x80 but stat() if called via syscall64. This is
    > a local property of the system call, not a global per process.

    I think, the documentation said that as soon as prctl() is used to set
    a bpf filter for system calls, it automatically disallows system calls
    using an entry point other than the one used by this particular
    prctl().

    I was trying to come up with scenarios where this particular approach
    causes problem, but I can't think of any off the top of my head. So,
    it might actually turn out to be a very elegant way to reduce the
    attack surface of the kernel. If we are really worried about userspace
    compatibility, we could make the kernel send a signal instead of
    terminating the program, if the wrong entry point was used; not sure
    if that is needed, though.


    Markus
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