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Re: Runtime failure running sh:qemu in -next due to 'sh: fix copy_from_user()'

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On Fri, Sep 16, 2016 at 10:31:41PM +0100, Al Viro wrote:
> On Fri, Sep 16, 2016 at 01:59:38PM -0700, Guenter Roeck wrote:
> > Yes, reverting 6e050503a150 fixes the problem.
> > 
> > I added a BUG() into the "if (unlikely())" below, but it doesn't catch,
> > and I still get the ip: OVERRUN errors. Which leaves me a bit puzzled.
> > 
> > Guenter
> > 
> > > The change in question is
> > >         if (__copy_size && __access_ok(__copy_from, __copy_size))
> > > -               return __copy_user(to, from, __copy_size);
> > > +               __copy_size = __copy_user(to, from, __copy_size);
> > > +
> > > +       if (unlikely(__copy_size))
> > > +               memset(to + (n - __copy_size), 0, __copy_size);
> > >  
> > >         return __copy_size;
> 
> So we don't even hit that memset()?  What the hell?  __copy_user() is
> declared as
> __kernel_size_t __copy_user(void *to, const void *from, __kernel_size_t n);
> 
> and __copy_size copy_from_user() is
> 
>         __kernel_size_t __copy_size = (__kernel_size_t) n;
> 
> So
> 	return __copy_user(to, from, __copy_size);
> and
> 	__copy_size = __copy_user(to, from, __copy_size);
> 	return __copy_size;
> ought to be doing exactly the same thing.  At that point it's starting to
> smell like a compiler bug somewhere in there.
> 
> Try to remove that (not triggered) if (unlikely(__copy_size)) memset(...)
> and see if that's enough to recover.  And it would be nice to see what
> all three variants (as it is, with commit reverted and with just that if
> removed) generate in e.g. sys_utimensat() (fs/utimes.s)

It would be useful to know what compiler version was used to build the
kernel. I wouldn't be surprised if some are buggy.

Rich

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Runtime failure running sh:qemu in -next due to 'sh: fix  copy_from_user()' Guenter Roeck <linux@roeck-us.net> - 2016-09-16 21:20 +0200
  Re: Runtime failure running sh:qemu in -next due to 'sh: fix  copy_from_user()' Al Viro <viro@ZenIV.linux.org.uk> - 2016-09-16 21:50 +0200
    Re: Runtime failure running sh:qemu in -next due to 'sh: fix  copy_from_user()' Guenter Roeck <linux@roeck-us.net> - 2016-09-16 23:00 +0200
      Re: Runtime failure running sh:qemu in -next due to 'sh: fix  copy_from_user()' Al Viro <viro@ZenIV.linux.org.uk> - 2016-09-16 23:40 +0200
        Re: Runtime failure running sh:qemu in -next due to 'sh: fix  copy_from_user()' Rich Felker <dalias@libc.org> - 2016-09-16 23:50 +0200
          Re: Runtime failure running sh:qemu in -next due to 'sh: fix  copy_from_user()' Guenter Roeck <linux@roeck-us.net> - 2016-09-17 00:50 +0200
            Re: Runtime failure running sh:qemu in -next due to 'sh: fix  copy_from_user()' Rich Felker <dalias@libc.org> - 2016-09-17 01:40 +0200
              Re: Runtime failure running sh:qemu in -next due to 'sh: fix  copy_from_user()' Guenter Roeck <linux@roeck-us.net> - 2016-09-17 04:30 +0200
              Re: Runtime failure running sh:qemu in -next due to 'sh: fix  copy_from_user()' Guenter Roeck <linux@roeck-us.net> - 2016-09-17 04:30 +0200
                Re: Runtime failure running sh:qemu in -next due to 'sh: fix  copy_from_user()' Rob Landley <rob@landley.net> - 2016-09-18 06:50 +0200
                Re: Runtime failure running sh:qemu in -next due to 'sh: fix  copy_from_user()' Rich Felker <dalias@libc.org> - 2016-09-18 17:20 +0200
        Re: Runtime failure running sh:qemu in -next due to 'sh: fix  copy_from_user()' Guenter Roeck <linux@roeck-us.net> - 2016-09-17 00:50 +0200
          Re: Runtime failure running sh:qemu in -next due to 'sh: fix  copy_from_user()' Al Viro <viro@ZenIV.linux.org.uk> - 2016-09-17 01:10 +0200
  Re: Runtime failure running sh:qemu in -next due to 'sh: fix  copy_from_user()' Al Viro <viro@ZenIV.linux.org.uk> - 2016-09-16 22:10 +0200
    Re: Runtime failure running sh:qemu in -next due to 'sh: fix  copy_from_user()' Guenter Roeck <linux@roeck-us.net> - 2016-09-16 22:40 +0200
      Re: Runtime failure running sh:qemu in -next due to 'sh: fix  copy_from_user()' lsorense@csclub.uwaterloo.ca (Lennart Sorensen) - 2016-09-16 22:50 +0200
      Re: Runtime failure running sh:qemu in -next due to 'sh: fix  copy_from_user()' Al Viro <viro@ZenIV.linux.org.uk> - 2016-09-16 23:30 +0200

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