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    SubjectRe: [RFC,PATCH 1/2] seccomp_filters: system call filtering using BPF
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    On Mon, Jan 16, 2012 at 12:37 PM, Oleg Nesterov <oleg@redhat.com> wrote:
    > On 01/13, Will Drewry wrote:
    >>
    >> On Fri, Jan 13, 2012 at 1:01 PM, Will Drewry <wad@chromium.org> wrote:
    >> > On Fri, Jan 13, 2012 at 11:31 AM, Oleg Nesterov <oleg@redhat.com> wrote:
    >> >>
    >> >> Me too. I see no point in using user_regs_struct.
    >> >
    >> > I'll rev the change to use pt_regs and drop all the helper code.  If
    >> > no one says otherwise, that certainly seems ideal from a performance
    >> > perspective, and I see pt_regs exported to userland along with ptrace
    >> > abi register offset macros.
    >>
    >> On second thought, pt_regs is scary :)
    >>
    >> From looking at
    >>   http://lxr.linux.no/linux+v3.2.1/arch/x86/include/asm/syscall.h#L97
    >> and ia32syscall enty code, it appears that for x86, at least, the
    >> pt_regs for compat processes will be 8 bytes wide per register on the
    >> stack.  This means if a self-filtering 32-bit program runs on a 64-bit host in
    >> IA32_EMU, its filters will always index into pt_regs incorrectly.
    >
    > Yes, thanks, I forgot about compat tasks again. But this is easy, just
    > we need regs_64_to_32().

    Yup - we could make the assumption that is_compat_task is always
    32-bit and the pt_regs is always 64-bit, then copy_and_truncate with
    regs_64_to_32. Seems kinda wonky though :/

    > Doesn't matter. I think Indan has a better suggestion.

    I disagree, but perhaps I'm not fully understanding!

    Thanks!
    will
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