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

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Message-ID: <a40f3834f953da91dee719c1a801761405dc4780.camel@intel.com>
Date:   Thu, 07 May 2020 10:11:25 -0700
From:   Yu-cheng Yu <yu-cheng.yu@...el.com>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Tony Luck <tony.luck@...el.com>,
        Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Rik van Riel <riel@...riel.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        sam <sunhaoyl@...look.com>, Kees Cook <keescook@...omium.org>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Jann Horn <jannh@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Potapenko <glider@...gle.com>,
        Al Viro <viro@...iv.linux.org.uk>, stable@...r.kernel.org
Subject: Re: [PATCH] x86/fpu/xstate: Clear uninitialized xstate areas in
 core dump

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