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    SubjectRe: [PATCH] x86/ptrace: Remove questionable TS_COMPAT usage in ptrace
    On Mon, Jun 20, 2016 at 9:14 AM, Oleg Nesterov <oleg@redhat.com> wrote:
    > On 06/20, Andy Lutomirski wrote:
    >>
    >> On Mon, Jun 20, 2016 at 8:24 AM, Oleg Nesterov <oleg@redhat.com> wrote:
    >> >
    >> > How about the simple change below for now? IIRC 32-bit task can't use
    >> > "syscall" so if syscall_get_nr() >= 0 then even the wrong TS_COMPAT is
    >> > not that bad, even if it "leaks" to user-mode.
    >>
    >> Hmm. That should fix the minor security issue, but it will even
    >> further break cross-arch tracing: now a 32-bit tracer tracing a 64-bit
    >> task that does int $0x80 will malfunction even more than it would
    >> have.
    >
    > This is broken in any case. I mean, a 32-bit debugger can't really
    > debug a 64-bit task.
    >
    > I don't think this change makes the things really worse.
    >
    >> Also, it relies on bizarre arch details IMO.
    >
    > Heh, it looks as if your patch do not ;)
    >
    >> I think I prefer my version, coming momentarily.
    >
    > I disagree... I don't really understand why do we need the additional
    > complications for the minimal fix which doesn't look very nice anyway.
    >
    > But I won't argue, and your patch looks correct to me.

    Part of the reason is that I actually want to fix this in two parts.
    After my TS_REGS_POKED_I386 patch, I have a follow-up patch that I
    want to polish and test a bit more that's intended to get the
    64-bit-tracer/32-bit-tracee case right, but it probably needs extra
    testing, is less likely to make 4.8, and is definitely not for
    4.7/stab.e. That patch deletes TS_REGS_POKED_I386 again. So by
    having the minimal fix be more mindless, I'm more comfortable with the
    backport. I'll send out the second patch soon.


    --Andy


    --
    Andy Lutomirski
    AMA Capital Management, LLC

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