Re: [PATCH] x86/fpu/xstate: Clear uninitialized xstate areas in core dump

[Yu-cheng Yu]

On Thu, 2020-05-07 at 18:56 +0200, Sebastian Andrzej Siewior wrote:
> On 2020-05-07 09:49:04 [-0700], Yu-cheng Yu wrote:
> > In a core dump, copy_xstate_to_kernel() copies only enabled user xfeatures
> > to a kernel buffer without touching areas for disabled xfeatures.  However,
> > those uninitialized areas may contain random data, which is then written to
> > the core dump file and can be read by a non-privileged user.
> > 
> > Fix it by clearing uninitialized areas.
> 
> Is the problem that copy_xstate_to_kernel() gets `kbuf' passed which
> isn't zeroed? If so, would it work clean that upfront?

Alexander Potapenko's patch (in the Link:) fixes the buffer in
fill_thread_core_info().  My patch prevents the same issue if this function is
called from somewhere else in the future.

Yu-cheng