[Bug runtime/14848] Reading user memory fails occasionally when it shouldn't

["dsmith at redhat dot com" <sourceware-bugzilla at sourceware dot org>]

http://sourceware.org/bugzilla/show_bug.cgi?id=14848

--- Comment #1 from David Smith <dsmith at redhat dot com> 2012-11-27 19:23:42 UTC ---
It looks like this is a "compat" issue. When we're doing a 32-bit executable on
a 64-bit kernel, user 'clock_settime()' ends up calling kernel
'compat_sys_clock_settime()', which looks like this:

====
long compat_sys_clock_settime(clockid_t which_clock,
        struct compat_timespec __user *tp)
{
    long err;
    mm_segment_t oldfs;
    struct timespec ts;

    if (get_compat_timespec(&ts, tp))
        return -EFAULT;
    oldfs = get_fs();
    set_fs(KERNEL_DS);
    err = sys_clock_settime(which_clock,
                (struct timespec __user *) &ts);
    set_fs(oldfs);
    return err;
}
====

I believe "access_ok()" is failing because the address that sys_clock_settime()
gets isn't a user address, it is a kernel address.

I don't know how to fix/workaround this yet.

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